RELATION OF PHENOLIC COMPOUNDS
TO GERMINATION OF PEACH SEEDS
JAMES BRUCE AITKEN
A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL OF
THE UNIVERSITY OF FLORIDA
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE
DEGREE OF DOCTOR OF PHILOSOPHY
UNIVERSITY OF FLORIDA
The author wishes to express his sincere appreciation and gratitude
to Dr. R. H, Biggs, Associate Biochemist, Department of Fruit Crops, and
Chairman of the student's Supervisory Committee, for his most valuable
assistance and guidance during the course of research and the prepara-
tion of this manuscript.
Appreciation is extended to Dr. A. H. Krezdorn, Chairman, Depart-
ment of Fruit Crops; Dr. T. E. Humphreys, Associate Biochemist, Depart-
ment of Botany; Dr. C. H. Hendershott, Associate Professor of Fruit
Crops; and Dr. D. 0. Spinks, Professor of Soils, Department of Soils,
for their constructive criticism and invaluable assistance in the pres-
entation of this manuscript.
The author also wishes to express his gratitude to Mr. J. K. Peter,
laboratory technician, for his assistance in conducting portions of the
For her help in the preparation of this manuscript and also for her
interest and encouragement during the course of this study, the author
wishes to express his sincere appreciation to his wife, Patricia.
TABLE OF CONTENTS
LIST OF TABLES iv
LIST OF FIGURES vi
REVIEW OF LITERATURE 3
Germination Inhibitors 4
Physiology of Seed Germination 12
Physiology of Peach Seed Germination 17
MATERIALS AND METHODS 21
EXPERIMENTAL RESULTS .^ 31
SUMMARY AND CONCLUSIONS 73
APPENDIX: GAS CHROMATOGRAMS OF STANDARDS 75
LITERATURE CITED 81
BIOGRAPHICAL SKETCH 90
LIST OF TABLES
1. Influence of thiourea concentrations on germination and
per cent of production of abnormal seedlings from
'Okinawa' peach seeds 32
2. Effect of thiourea concentration and embryo excision on
germination of 'Okinawa' peach seeds 12 days after
start of imbibition and on abnormal seedling production
32 days after start of imbibition 33
3. Per cent germination of 'Okinawa' peach seeds 7 and 20
days after start of imbibition as influenced by cyanide ... 34
4. Per cent germination of 'Okinawa' peach seeds 7 and 12
days after start of imbibition as influenced by
5. Per cent germination of 'Okinawa' peach seeds 7 and 12
days after start of imbibition as influenced by
6. Relative retention time and possible identity of com-
ponents separated by gas chromatography of the propyl
esters of the acidic fraction from an ethanolic
extract of peach seeds 40
7. Paper chromatographic separation of the inhibitory
complex from dormant peach seeds 42
8. Influence of acids, bases and heat on the inhibitory
complex from peach seeds after paper chromatography 43
9. Solubility of the inhibitor-complex in various organic
solvents as determined by the alfalfa bioassay 44
10. Mean per cent germination of dormant 'Okinawa' peach
seeds 30 days after start of imbibition as influenced
by benzaldehyde and mandelonitrile concentrations 57
11. Mean per cent germination of dormant 'Okinawa' peach
seeds 30 days after start of imbibition as influenced
by benzoic and p-hydroxybenzoic acid concentrations 58
12. Comparison of retention times of p-hydroxybenzoic acid
and L-mandelic acid as influenced by various acetylation
13. Comparison of peak areas of p-hydroxybenzoic acid and
L-mandelic acid as influenced by various acetylation
LIST OF FIGURES
1. Influence of benzaldehyde and mandelonitrile on peach
seed germination 38
2. Gas chromatogram of the propyl esters of the acidic
fraction from an ethanol extract of peach seeds.
Time is in minutes 39
3. Gas chromatograms of a known composite sample of an
etheral solution of benzaldehyde-mandelonitrile:
(a) initial solution; (b) after addition of a
solution of sodium bisulfite; and (c) after addition
of potassium cyanide 47
4. Changes in benzaldehyde-mandelonitrile content of
peach seeds as measured at various intervals after
start of imbibition under the designated treatments 48
5. Change in the content of mandelonitrile in peach
seeds at various intervals after start of imbibition
under the designated treatments 49
6. Change in the content of benzaldehyde in peach seeds
at various intervals after start of imbibition under
the designated treatments 50
7. Germination of peach seed as influenced by embryo
excision, and thiourea treatments as determined
periodically after the start of imbibition 52
8. Relative inhibitory activity, as measured by the
alfalfa bioassay, of the inhibitory complex in an
ethanolic extract of peach seeds chromatographing
between R^'s 0.6 to 0,8 54
9. Germination of peach seeds as influenced by 5° C
of varying durations 55
10. Gas chromatogram of diazomethane-solvent control.
Retention time is in minutes 60
11. Gas chromatograms of L-mandelic acid(a) and
p-hydroxybenzoic acid(b) treated for 30 minutes
with diazomethane. Retention time is in minutes 61
12. Gas chromatograra of an ethanol extract from peach
seeds treated for 30 minutes with diazomethane.
Retention time is in minutes 63
APPENDIX: Gas chromatograms of standards.
13. Gas chromatograms of the propyl esters of benzoic
acid(a) and mandelic acid(b). Retention time in
14. Gas chromatograms of the propyl esters of o-hydroxy-
benzoic acid(a) and p-hydroxybenzoic acid(b) . Reten-
tion time in minutes 77
15. Gas chromatograms of the propyl ester of 2, 6-dihydroxy-
benzoic acid. Retention time in minutes 78
16. Gas chromatograms of the propyl ester of 2,4-dimethoxy-
benzoic acid. Retention time in minutes 79
17. Gas chromatograms of the propyl ester of o-hydroxy-
cinnamic acid. Retention time in minutes 80
The phenomena of seed dormancy have interested researchers for many
years. Little by little the details are being unfolded in various plant
species. Seed dormancy may result from such sources as mechanical re-
striction, immature embryo, or chemical inhibition.
Various chemicals, e.g., thiourea, have been found which will termi-
nate seed dormancy, but in many cases this results in the production of
abnormal seedlings (36, 37, 76, 97) . However, reports in the literature
show that abnormalities may be due to temperature (80) .
The breakdown of amygdalin in germinating peach seeds possibly
presents a fruitful area for investigating seed dormancy. Amygdalin is
hydrolyzed to mandelonitrile and glucose by prunsin (104). Mandelo-
nitrile is further hydrolyzed by emulsin to cyanide and benzaldehyde
(104). It has been shown previously that benzaldehyde strongly affects
growth (46) . Phenolic compounds have been isolated from many plant
tissues (39, 82, 92, 93, 94) and their influence on certain biochemical
systems within the plant has been investigated (38, 74, 78, 79, 83, 95,
105) . Recent evidence would indicate that they are involved in plant
growth and development (78, 105). Therefore, phenolic compounds could
play a prominent role in controlling dormancy of peach seed.
With this knowledge at hand, research was undertaken to determine
the role of phenolic compounds in peach seed germination. It was recog-
nized that this role could be stimulatory, inhibitory, both, or neither.
Also various means of terminating dormancy were compared with regard to
their influence upon certain of the phenolic compounds. In order to
conduct this investigation, several new techniques were established for
isolating and aiding in the identification of certain of the phenolic
REVIEW OF LITERATURE
In many plants the phenomena of seed dormancy, regardless of cause,
have a survival benefit. The temi "dormancy" as applied to viable seeds
is generally restricted to those which fail to germinate in a reasonable
length of time when subjected to an adequate moisture supply, a temper-
ature within the range of 18-30° C and the normal gaseous composition of
the atmosphere. Dormancy can be due to various causes. It may be due
to the immaturity of the embryo, impermeability of the seed coat to
water and/or gases, prevention of embryo growth by mechanical restric-
tions, special requirements for temperature or light, endogenous factors
which inhibit germination, age of seed, and, in certain cases, immaturity
of the embryo. These factors have been discussed in several classic
reviews on seed germination (16, 17, 24) and in some excellent reviews
in the last several years (64, 96, 102, 108). This review will be par-
ticularly concerned with endogenous factors which control seed dormancy
since this is the type of dormancy we are dealing with in the case of
peach seeds (11, 14, 36).
Viable seed that fail to germinate when exposed to conditions
generally considered favorable for germination can be induced to germi-
nate in most cases by the correct exposure to certain environmental
factors. Very often the environmental cue for the resumption of growth
is attained from climatic components, e.g., low temperature of a given
duration, alternating periods of moisture stress, daylength, etc. These
environmental components precondition tho socvis, so th;\l gormination
occurs when they are supplied with adequate moisture, a warm temperature
and atmospheric gases of the normal composition. After-ripening may be
defined as physiological changes occurring in any part of the seed which
enable the seed to germinate and the seedling to grow normally (64) .
The necessity for a period of after-ripening may be due to several
factors. In the case of the immature embryo, further developmental
changes may be required before germination (115). In other seeds,
chemical changes must occur in the embryo before they germinate (64) .
In still others, chemical changes must occur in the integuments and/or
other tissues associated with the embryo (96).
In contrast to seeds which will not germinate until subjected to
certain environmental factors before being placed under favorable germi-
nation conditions of moisture, warm temperature and atmospheric gases,
some seeds will gem;inate readily without preconditioning. However, it
is interesting to note that the latter will also lose their readi.ioss to
germinate if subjected to stress conditions much the same as seeds that
require factors to terminate dormancy (65, 98). This phenomenon is
referred to as secondary dormancy. Secondary dormancy can be induced
in certain seeds by subjection to high or low temperatures, high COg
levels or continuous light.
A large number of substances are capable of inhibiting germination.
Those compounds which are generally toxic to living organisms will also,
at toxic concentrations, prevent germination simply by killing the seed.
However, these compounds have been of little value in determining the
underlying causes of dormancy. Compounds which prevent germination
without killing the seeds are by far the more valuable in determining
the mechanism of dormancy.
The simplest type of inhibition is caused by non-toxic chemicals
in high concentration and this has been shown to be due to high osmotic
pressures (16). These high osmotic conditions may be obtained by in-
organic salts, sugars, or other substances. An example of such inhibi-
tion is the inability of seed within some mature fruit to germinate.
The large quantities of soluble solids present in the flesh create high
osmotic conditions around the seed and prevent germination. The thresh-
old of osmotic pressure which prevents germination differs with the
species. As soon as the seeds are removed from the high osmotic environ-
ment and placed in water, they will germinate (64).
A more complex type of inhibition is that caused by substances
which are known to interfere with certain metabolic pathways. Since
germination cannot occur without active metabolism, any substance that
would alter normal metabolism, would probably alter the germination
pattern of seed. Compounds such as cyanide (4), dinitrophenol (68),
azide (68), fluoride (24), hydroxylamine (24), and others (4, 24) which
are respiratory inhibitors, have inhibited germination at concentrations
approximating those which inhibit metabolic processes. Therefore, it
seems that inhibition of germination by this class of compounds is a
result of their effect on metabolism (64), but only in the case of
cyanide (4) have these chemicals been implicated in natural seed
Another class of compounds that inhibited germination are auxins
(54). An example of such a case would be the use of low concentrations
of 2,4-dichlorophenoxyacetic acid (2,4-D) to inhibit germination. Al-
though auxins have been shown to be necessary for growth of isolated
embryonic tissues and to increase at the time of germination or shortly
before (32, 51); however, there has been no convincing evidence that
they are directly involved in the dormancy mechanism (25, 42, 55). Only
in a few instances (14, 25, 37) have auxins been shown to stimulate
germination and these instances were cases where the dormant state of
the seed was altered by pretreatments. This is in contrast to the in-
fluence of auxins on fruit growth and development (59, 60, 61).
On the other hand, growth inhibitors are of general occurrence in
dormant seeds, and there is abundant evidence for their involvement in
the physiological mechanisms of dormancy.
Evidence for the involvement of growth inhibitors in seed dormancy
is the demonstration that they are often present in dormant seeds and
that the application of such materials can impose dormancy on seeds in
certain cases. Nutrile (70) was the first to show this. He applied
coumarin to lettuce seeds and showed they required preconditioning again
before they would germinate. These experiments were substantiated by
Evenari (25) .
Many phenolic compounds have been found to inhibit germination.
These have a widespread occurrence and distribution in plants and
fruits and thus it is thought that tliey may occur as natural germination
inhibitors (92). It was suggested by van Sumere (92, 93) that the
phenolic compounds may be classified along with coumarins as dormancy
inducing agents. Coumarin, ferulic acid and other phenolic compounds
have been found to occur in the skin as well as the cortical tissue of
potato and Hemberg (42, 43) suggested that the rest period of the
potato may be due to an abundance of growth inhibiting substances in the
periderm. Koves and Varga (53) surveyed the dry fruits of several
species with reference to inhibitory substances. Inhibitors were found
in all fruits and those that have been chemically identified were
phenolic acids or their depsides and polydepsides. Numerous benzoic and
cinnamic acid derivatives such as high molecular weight tannic acids,
protocatechuic, caffeic and chlorogenic, ferulic, p-coumaric and p-
oxybenzoic acids had a lesser activity (53) . Salicylic acid, and in
some cases unidentified cinnamic acid derivatives, had strong activity.
Most of these inhibitors were washed out or destroyed as the fruit re-
mained on the tree for a prolonged period of time.
Although the phenolic substances range in structure from simple
phenols to complex compounds, such as lignin, it seems that the most
important phenols, insofar as growth regulation is concerned, are the
• monocyclic aromatic compounds (82) . In recent years attention has been
given to the role of hydroxycinnamic and hydroxybenzoic acids in plant
growth and development. The biosynthesis of these acids in higher
plants has received renewed attention recently (22, 82, 94). The major
pathway for the formation of these compounds undoubtedly involves
phenylalanine via shikimic acid. The inter-conversion of the hydroxy-
benzoic acids gave rise to many derivatives (39, 45, 50). p-Hydroxy-
benzoic acid and caffeic acid have been isolated from plants and shown
to be active as growth regulators (103, 105). Other phenolic compounds
that have shown lesser activity include salicylic, gallic, ferulic,
caffeic, vanillic, protocatechuic, chlorogenic, p-oxybenzoic, and pr
coumaric acids (53, 64, 92).
Another possible function of the phenolic acids in seed genr.:: na-
tion may be their role in the synthesis and degradation of indoleacetic
acid (lAA) (74, S3). Pilet (78, 79) reported that the mono-hydroxyben-
zoic acids increased the iii vitro destruction of lAA. Of these, p-hy-
droxybenzoic acid had the greatest effects, causing stimulatory growth
of stem sections at low concentrations and inhibiting elongation at higher
concentrations. Many other naturally occurring phenolic acids were
studied by Zenk and Muller (116) as to their influence on the destruc-
tion of exogenously applied lAA. By growth experiments with IAA-l--'-'^C
and determination of the -^^CO^ evolved, it was shown that monophenols
stimulate the decarboxylation of lAA under conditions where growth was
suppressed (95). When Mn++ was present, this decarboxylation was enhanced.
To add to the complexity of the relation of phenols to growth, Gordon and
Paleg (38) have shown that phenols, under conditions leading to their
oxidation, reacted with tryptophan to form lAA .
Probably the most active and most widely used gemiination inhibitor
is coumarin. Coumarin is characterized by an aromatic ring and an un-
saturated lactone structure. No single group in the coumarin molecule
has been shown to be the cause of its inhibitory action. Reduction of
the unsaturated lactone ring or substitution by hydroxyl, methyl, nitro,
chloro and other groups in the ring system reduced the inhibitory activi-
ty (63, 70).
The flavonoid, naringenin, which has been isolated from peach buds
by Hendershott and Walker (44), has an action similar to coumarin on
lettuce seeds. Phillips (77) demonstrated that it will impose dormancy
on lettuce seeds that can be reversed by light or by aj^'plication of
Recently, several new compounds have been isolated which exhibited
growth regulatory properties. One group of compounds which show a
marked elongation effect on rice and lettuce is related to helmintho-
sporol (84). 'Dormin', a terpenoid compound has shown a marked influence
on the regulation of bud growth in some woody plants. It appears that
the structure of 'dormin' and 'abscisin II' are the same (15, 71).
Eagles and Wareing showed that an inhibitor v dormin') concentrated from
an extract of birch leaves could completely arrest apical growth when
applied to the leaves of seedlings. Evidence was also found for high
levels of 'dormin' in birch leaves under short days, with the emergence
from dormancy presumably resulting from an interaction between 'dormin'
and growth-promoting substances (20, 21). A recent finding in the study
of dormancy regulation in peach seeds was that an inV.ibitor isolated
from the seed integuments chromatographed identical to 'dormin' (57, 58).
However, Daley (18) has shown that several inhibitors are present in
peach seed cotyledons and that several chromatographed in the zone
labeled 'dormin' by Lipe and Crane (58).
Bennet-Clark and Kef ford (8) first described a complex o^ inhibitory
substances that appeared on paper chromatograms of plant extracts running
ahead of lAA when developed in a solvent of i sopropanol/ammoni a/water .
This inhibitory area, possessing R^ values of 0.6 to 0.8, has been clas-
sified as the beta-inhibitor complex (48, 49). This inhibitory complex
has been shown to be widespread in plants and has been related to both
dormancy and correlative growth. For instance, Varga (100) has reported
that the juice of lemons, strawberries and apricots contains inhibitors
which appear to correspond to the beta-in'iibitor complex. Lipe (57)
found that the inhibitors in 'Lovell' peach seeds are similar to the
beta-inhibitor complex. Elution and rechroraatography of the beta-in-
hibitor-complex has yielded both acidic and neutral substances (56).
Recently, the beta-inhibitor-complex concentrated as acidic compounds
from extracts of dormant maple buds was shown to be a complex of phenolic
substances (86). It includes coumarin and salicylic, ferulic, p- and
o-coumaric, m-oxybenzoic acid (93, 108) and 'dormin' (15).
Many of the previously mentioned phenolic compounds have been found
to occur in various plant tissues, especially in fruits (64, 108). ?or
example, Varga (100) and Koves and Varga (53) have shown that many
phenolic compounds such as salicylic, ferulic, caffeic, chlorogenic,
p-coumaric, protocatechuic and p-oxybenzoic acids are present in fruits.
Along these same lines, it is interesting to note that peach juice is
injurious to peach seed germination (85), It has been suggested that
the inhibition of seed germination in fruit was generally not due to a
single compound but was due to the synergistic action of several com-
pounds that might be present within the fruit or the seed itself (lOS).
The activity of endogenous inhibitors may not be solely directed
at the prevention of germination per se , but may also influence some of
the other factor's controlling dormancy. Black and Warding (10) reported
that the removal of the embryo from intacx seed reduced the light re-
quirement for germination of seed of the Betula spp. They also suggested
that the inhibitor in the seed coat increased the oxygen requirement of
the embryo. Wareing and Foda (109, 110) found that leaching the embryo
of Xanthium seed removed the inhibitor and that maintaining the seed in
a pure oxygen atmosphere cause.' a reduction in the inhibitor within 30
hours. Elliott and Leopold (23) showed that the inhibitors from Avena
seeds inhibited alpha-amylase activity.
Villiers and Wareing (106, 107, lOS) reported that chilling Fraxinus
excelsior seeds had no effect on the activity of the inhibitor but that
dormancy was overcome during chilling by production of a growth stirau-
lator in the embryo tissues. Flemion and De Silva (31) also demo. rated
with peach seeds that with the bioassay they were using they coul^ I'ind
little correlation between growth inhibitors and the termination of
The promotive effects of oxygen on germination of seeds and the
parallel effects of light led Paech (73) to suggest ^r.a'c dorr.iancy was
regulated by phenolic substances in the seed coat. The oxidative activi-
ties of phenolic compounds could trap oxygen, preventing its entry into
the seed. The action of the phenolics could be blocked by oxygen or
light through the photooxidation of the phenolics themselves.
The effects of gibberellin in breaking the dormancy of many seeds
indicated that it could possibly be the stimulator of growth if it were
formed during the period in which donriancy was broken (35) . Murakami
(66) has shown gibberellin to be present in a wide diversity of seeds.
As seeds of Avena f atua emerged from dormancy a growth-promoting sub-
stance suggestive of gibberellin was formed (67). These seeds were also
brought out of dormancy if soaked in gibberellin solutic.-s. Kahn (47)
reported gibberellin overcame dormancy of lettuce seed regardless of
whether it was imposed by hi^... temperature, by far-red light, or by
Recently, a mode of action was suggested for gibberellic acid (99).
It has been reported that gibberellic acid stimulated alpha-araylase
production in the aleurone layer of _ coat of cereals which in turn
increased the rate of starch hydrolysis. Th ' stimulation of alpha-
amylase was believed to be due to the direct influence of gibberellic
acid on messenger RNA polymerase, an enzyme that is involved in producing
the alpha-amylase enzyme (101).
Physiology of Seed Germination
The actual germination of a seed reflects the cumulative effect of
interactions between many factors both external and internal. These
factors range from hereditary traits to environmental influences during
development and storage. For simplicity of this review, the influencing
factors will be grouped into external and internal factors. Excellent
reviews have been published on the physiology of seed germination (16,
17, 24, 64, 96, 102).
Among the external factors required for seed germination are an
adequate supply of moisture, a suitable temperature range and composi-
tion of gases in the atmosphere, light, and sometimes certain chemicals.
The requirement for these conditions varies according to the species
and variety and is determined by hereditary factors and by the condi-
tions which prevailed during seed formation. Frequently it appears
there is a correlation between the environmental requirement for germi-
nation and the ecological conditions occurring in the habitat of the
plant and the seeds (64).
Water ; One of the first processes which must occur for germination
of dry seeds is the uptake of water. The extent of this uptake is deter-
mined by (a) the composition of the seed coat, (b) the permeability of
the seed coat to water, (c) the availability of water (liquid or gaseous)
in the environment, and (d) soluble solids (64).
Gases : Germination, a process of living cells, requires an expendi-
ture of energy. Energy requiring processes in living cells are usually
supported by processes of oxidation, in the presence or absence of
oxygen. These processes, respiration and fermentation, involve an ex-
change of gases, an output of carbon dioxide in both cases and the uptake
of oxygen for respiration. Consequently, seed germination is markedly
affected by the composition of the ambient atmosphere (64).
The partial pressure of oxygen in the atmosphere can be reduced
considerably without greatly interfering with the rate of respiration.
In fact, the seeds of some water plants germinate better under lower
oxygen tensions than in air. Seeds of many terrestrial plants can
germinate under water where the concentration of oxygen often corresponds
to a partial pressure of oxygen very much less than that of the atmos-
In the early stages of germination of seeds of species such as
Pi sum sativum , respiration is largely or almost totally anaerobic be-
cause of the relative impermeability of even hydrated seeds of such
species to oxygen. As soon as the seed coats are ruptured, aerobic
respiration replaces the anaerobic oxidative processes (65).
The influence of carbon dioxide concentration is usually the re-
verse of that of oxygen. Many seeds fail to germinate when the carbon
dioxide tension is high. There seems to be a minimal requirement for
carbon dioxide in order for germination to occur in Atriplex halimus
and Salsola as well as lettuce whereas some other species of Atriplex
are resistant to high levels of carbon dioxide as long as the oxygen
concentration is kept constant (7).
Temperature : Different kinds of seeds have specific ranges of
temperature within which they germinate. Very low and very high temper-
atures tend to prevent the germination of all seeds. A rise in temper-
ature does not necessarily cause an increase in either the rate or the
percentage of germination. Therefore, germination is not characterized
by a simple temperature coefficient (107),
Light ; Among cultivated and non-cultivated plants there is con-
siderable evidence for light as a factor influencing germination. For
example, lettuce, tobacco and many crucifers require light to germinate
(33, 75, 77, 96). Seeds may be divided into those which germinate only
in the dark, those which germinate only in continuous light, those which
germinate after being given a brief illumination and those which are in-
different to the presence or absence of light during germination (96),
Studies have shown that different spectral zones affected germina-
tion differently. Light of wavelength less than 2900 A° has inhibited
germination of all seeds tested (33). Between 2900 A° and 4000 A° the
germination of some seeds is inhibited (33). In the visible range,
4000 AO - 7000 A°, it was shown that light in the range of 5600 A° -
7000 A and especially red light, usually promoted germination (64, 75).
If seeds exposed to red light were followed promptly by an exposure to
far-red light (7350 A ), germination was partially or totally inhibited
(65), An excellent review of the phytochrome system and its relation to
germination has been made by Siegelman and Butler (87) ,
The changes which take place during the germination process are to
a certain extent determined by the type of seed and its chemical compo-
sition. The composition is in turn influenced by environmental condi-
tions present durin^ seed formation as well as the hereditary factors of
the species involved.
Once the germination process is initiated, there is mobilization
and translocation of compounds from storage organs to the actively grow-
ing meristematic tissues (64). Studies with tree peony embryo and endo-
sperm tissues reveal that biochemical changes which take place with
germination are different for tissue af xer-ripened at 5° C from those
that are kept in the greenhouse at 21° - 30° C. The latter can be con-
si-dered dormant tissue (5, 6, 27). Major biochemical changes in organic
acids, amino acids and sugars were noted. These typify what has been
found with many seeds. A good discussion of this aspect of seed germi-
nation can be found in the book by Mayer and Poljakof f-Mayber (64).
Since phosphates play an extremely important role in a variety of
reactions of seeds, some discussion of the metabolism of phosphorus-
containing compounds would be in order. The phosphates are required for
the formation of nucleic acids which in turn are intimately concerned
with protein synthesis and the hereditary constitution of plant cells.
They are components of many other .;ey compounds including phospholipids
which function in controlling surface p:.-operties and permeability of
cell membranes. Also, the various phosphorylated sugars and nucleotides
are very closely linked with the energy-producing processes in the cell
during germination (64).
Phosphoi-us pi'imar^ly appears in seeds as organic phosphorus, v.'ith
very little being present as inorganic orthophosphate. Phytin is fre-
quently present and may constitute up to S0% of the total phosphorus
content of ..e seed (64). Since most of the phosphate :.3 present in the
bovind foi^, o.'jaophosphate may be the limiting factor in certain of the
reactions of the germination process. With this in mind the large amount
of phytin present may be considered as a reserve of inorganic phosphate
which can be liberated t. germinatio. proceeds by phosphatase activity
or more specii' cally phytase activity. Phytir, is also present in the
embryo, disappearing rapidly during germination. The phosphorus is
replenished by transport from the endosperm to the embryo during germi-
nation (2) . The rate of phytin hydrolysis and subsequent transport of
phosphorus to the growing sites pr^^sents a possible limiting facxor for
the race of germination and subsequent seedling development.
Recently, reports of myo -inositol acting as a growth factor in
plant tissue have .^een made (3). This is of particular interest in re-
gard to phytin since it is the salt of phytic acid or inositol .exaphos-
phate. The "neutral fraction" of coconut milk contains myo-inositol
along with scyllo -inositol and sorbitol, but myo- inositol was regarded
as the most important, as far as activity in grov/th-stimulation was
concerned. Myo- inositol may stiir.ulate the growth of seedlings and the
germination of certain seeds. In addition, myo -i..ositol has stimulated
growth of callus in cultures of elm ( Ulmus campestris ), Norway spi'uce
( Picea abies ) , tobacco ( Xicotiana tabacium ) , Vinca rosea , and carrot
(normal and tumorous) tissues (3) .
Studies on the nucleotide content of seeds during germination dis-
closed that the ATP content rose initially during imbibition and then
decreased (54). The content of nicotinamide adenine dinucleotide (NAD)
and nicotinamide auonine dinucleotide phosphate (NADP) in seeds and
sec "lings rises in all cases during germination. During the early
stages of germination there was a net increase in the RNA of peanut
cotyledons (102). Some of this RNA synthesis was thought to be associ-
ated with increased numbers of mitochondria, or in mitochondrial function,
and the ability of the cells to form chloroplasts. However, a part of
the increase was postulated to be associated with the appearance of
enzymes required for metabolism of the storage materials in the peanut.
A peak was reached in about 8 days followed by a more or less parallel
decline in RNA content and enzymic activities. These declines were con-
comitant with an increase in RNase activity.
As germination proceeded there was a sharp rise in carbon dioxide
evolution and a gradual rise in oxygen uptake of pea seeds. However,
after 24 hours there was a sharp decrease in the respiratory quotient
(SS) . This same pattern was observed for wheat for both carbon dioxide
evolution and oxygen uptake (67).
The energy pathways in seeds have been studied in some detail.
Both glycolysis and the organic acid metabolism have been observed in
germinating seeds (68, 91). Evidence for the presence of the pentose
phosphate-shunt pattern of metabolism has been found in mung beans (13).
In seeds containing large quantities of fats and oils, the tricarboxylic
acid pathway of metabolism may be partially replaced by the glyoxylate
pathway of metabolism which is a modified form of the tricarboxylic acid
cycle (52, 62, 68, 114). The glyoxylate pathway functions in the con-
version of fats to sugars.
Physiology of Peach Seed Germination
Peach seeds are characterized by a requirement for a period of low
temperature for natural termination of dormancy. Chemicals have been
found that will induce germination of dormant seed. These factors and
others are discussed below.
The optimum temperature of 5° C with a range of 5-10 C for 60-90
days has been found best suited for the termination of dormancy of peach
seeds (12, 16, 19, 29). The duration needed varies with varieties.
Some varieties require fewer hours of chilling to break dormancy than do
others (12). If a warm temperature treatment immediately follows ex-
posure of seeds to low temperatures, the growth capacity of the seeds
will be greatly reduced (14, 80). The reduction in growth capacity can
subsequently be restored by subjecting the seeds to additional exposures
to low temperatures.
Observations indicate that peach seeds are indifferent or day-
neutral toward the influence of light on germination (R. H. Biggs, Un-
It has been observed that the amount of free water present during
germination will influence the process. If seeds were allowed to be in
contact with free water, as in a petri dish, they generally became
bloated as a result of too rapid an uptake of water. However, if the
seeds were placed in moist vermiculite, they were not bloated (36).
This has been shown to occur with other types of seeds, particularly the
legumes (64) .
External : Tukey and Carlson (97) showed that applications of
thiourea to dormant 'Lovell' peach seeds induced germination. Evidence
obtained by Garrard (36) indicated that both the sulfhydryl and the
imido group are requisite to the activity of thiourea. Mercaptoethanol,
mercaptoethylamine, and urea were not effective either alone or in com-
bination in promoting germination of 'Okinawa' peach seed (76). The
induction of germination of dormant peach seeds has resulted in the
formation of abnormal seedlings when induction was by means of thiourea
or seed coat excision (2S, 36, 37, 97). However, it has been recently
sho\vn that the temperature during germina"c;.on plays a major role in the
development of abnormalities in the seedlings (SO) and that warm temper-
atures during treatments with chemicals or by embryo excision was re-
sponsible for increasing the severity of abnormalities (9) and not the
treatments. Thus, it is possible that two mechanisms are functioning
within the embryo; one that breaks dormancy and initiates germination,
and another which controls the development of the epicotyl.
Gibberellic acid has been found to induce the germination of dorraant
peach seeds but by a different mode of action than that of thiourea (76).
Gibberellic acid can decrease, to some extent, the occurrence of leaf
anomalies on peach seedlings and stimulate stem elongation (30). It is
possible that gibberellic acid has a modifying influence on both germi-
nation and epicotyl development.
Internal : Pollock and Olney (72, 81) have studied extensively -.le
i-est period of seeds of sour cherry, Prunus cerasus , with respect to
metabolic changes and growth. Their results showed that during low
temperature treatment to terminate donaancy, nitrogen and phosphorus
are translocated from the cotyledons to the embryonic axis of the embryo.
The rate of translocation of nitrogen was equal to the rate of cell
division; therefore, the nitrogen content per call seemed to remain ' '' v
constant. The rate .^f translocation of phosphorus was in excess of
cell division and the phosphorus concentration in the cells increased.
The experiments indicated that the translocated phorphorus was incorpo-
rated into all phosphate compounds in the cells. In fully 'curgid seeds
kept at warm temperatures, phosphorus tended to accumulate as inorganic
phosphate rather than in organic metabolites. These authors suggested
that the rest period may be associated with a block in the phosphate
metabolism of the cells. This hr -• not "aen substantiated at th : present
Pollock (SO), using 'Elberta' peach seed, suggests that the causal
agent of the dwarfing effect in seedlings is independent of the growth
inhibitor content of the seed. The physiological and anatomical a._ .octs
of dwarfing suggested a control by a self-duplicating system loci:.lized
in a limited region of the apical meristem and transmitted only by cell
division. This system was temperature sensitive during the time between
the first visible root growth and shoot elongation.
Investigations have been made into the effect of the degradation
products of the glucoside amygdalin within the seed. Upon imbibition,
mandelonitrile could be detected in the seeds (1); it was assumed to
have arisen from the hydrolysis of amygdalin to mandelonitrile and
glucose by prunsin. The mande_onitrile was further hydrolyzed to
cyanide and benzaldehyde (104), presumably by emulsin.
The presence of benzaldehyde during imbibition, as a result of the
degradation of ainygdalin, suggested that possibly .^enzoic acid and some
cf its derivatives m.\y be formed (25, 104). An alternative to this
pathway is that in which man^lelic acid, formed from r..- ndelonitrile,
undergoes enzymatic conversion to benzoic acids (40, 41, S9).
This study will be concerned with the changes in phenolic compounds
during the breaking of iorraancy and subsequent germination of the seed.
MATERIALS AND METIiODS
All seeds were obtained from the I960 and 1966 crops of Prunuf
persica cv, 'Okinawa'. This m:.'^orial was chosen for several reasons.
Principally, the seeds are relatively homozygous in respect to the chill-
ing requirement to temiinate seed dormancy (9), the seeds require a rel-
atively shoi-t period of low temperature stratification to overcome the
dormant state (9), and when the embryos are excised they germinate readi-
ly without any apparent abnormalities if the temperature range during
germination is 18-25° C (76).
The seeds were removed from the endocarp just prior to each experi-
ment and allowed to imbibe water from moistened vermiculixe. Depending
upon the nature of the expei'iment, the time in moistened vermiculite
varied. The seeds were planted in seed flats containing a 2:1 mixture
of perlite: vermiculite. Techniques for each experiment will be dis-
Tests for interaction of thiourea and seed coat excision on germi-
nation : In order to determine the most effective thiourea concentration
to promote the greatest amount of gerrainatioii with the least amount of
anomolous growth, a range of concentrations was tested. This was as
follows: 0.0, 1.0, 3 x lO"-*-, 10" and 10""^ M thiourea. The seeds were
kept in a moist medium for 42 hours and then followed by 6 hours' soaking
in the respective thiourea concentrations. Before imbibition, the seeds
were surface sterilized for 3 minutes with a 1,000 ppm raerthiolate in
25% ethanol: water solution. After the soaking period, the seeds were
blotted and planted in flats and kept in the dark at 20° C for 16 days
before being placed in a greenhouse. Each treatment was replicated 3
times with 40 seeds per replication.
A second experiment was designed to determine if any interaction
existed between thiourea and the seed coat on the degree of anomalous
development of the subsequent seedlings. Thiourea concentrations of
0.0, 10" , and 3 x 10~ M were applied to intact seeds and to excised
embryos after 42 hours imbibition. After a 6 hour treatment period,
the seeds were removed from the solutions, blotted, and planted in seed
flats. At 3 time intervals of 24, 48 and 72 hours, seed coats were re-
moved from samples of intact seeds treated with thiourea and the excised
embryos replanted. All treatments were kept in the dark at 20° C for 10
days, except for brief period of examination. After 10 days the flats
were moved to the greenhouse. Each treatment was replicated 3 times with
9 seeds per replication.
Testing chemicals for modification of germination of peach seeds :
Benzaldehyde, benzoic acid, cyanide, p-hydroxybenzoic acid and mandelo-
nitrile in a series of concentrations were tested on seed germination.
Because of volatility and water solubility of the chemicals, methods of
treatment varied. Each treatment was replicated 3 times with a random-
ized block design and observation on germination were taken at 7 and 12
days after the start of seed imbibition in all cases. Data was analyzed
statistically using F test and Duncan's multiple range (90),
In the cyanide treatments, the concentrations used were 0,0, 1.0,
-1 -9 -2
10 , 3 X 10 , and 10 M made with potassium cyanide. Seeds were
allowed to imbibe for 42 hours, seed coat removed and the embryos placed
in an aqueous solution of the chemical for 6 hours. They were then
planted in seed flats and placed in a growth charaber with a controlled
temperature of 20° 1 2° C and a 12-hour day of approximately 900 ft-C
Benzoic acid and p-hydrox; ;;enzoic acid were tested at concentrations
of 0.0, 10"^, 3 X 10~2, 10"^, and 10"^ M. To test the respective concen-
trations of each compound, approximately 5 g- of dry perlite were placed
in 100 ml beakers and the perlite saturated with the solution of che.uical
to be tested. After equilibration of the mixture, fully turgid seeds,
attaining this condition in moist vermiculite in 48 hours at 20° C, were
placed in the perlite plus chemical media, and maintained under aerobic
conditions. After 5 days in the media, the seeds were transferred to
flats i:untaining a 2:1 mixture of perlite: vermiculite. All ;.. .?es of
the experiments were conducted in growth chambers at 20° ^ 2° C with a
12-hour day of 900 ft-C. light intensity.
Since benzaldehyde and mandelonitrile are only slightly soluble in
water, the method of treatment was modified. For these tests, a loga-
rithmic range of quantities of the material per unit of perlite was used.
A measured amount of the chemical was absorbed onto fine perlite and
water added to the medium. The concentrations noted are based on the
amount that was available to the water phase. Five grams of the mixture
were used per container per ti'eatment and care was taken to maititain
aerobic conditions. For preparation of the seed before treatment, they
were allowed to imbibe for 4S hours, embryos excised and placed in the
perlite-chemical ...rixture. The embryos were left in the media for 5
days at 20 C. Thei. they were removed fi'om the chemical environments,
planted in flats and placed in a greenhouse for the remainder of the
Extraction and preparation of fractions from seeds for gas chroma-
tography : The isolation of the fractions was made from seeds that were
fully turgid after 4S hours in moist vermiculite at 20 C. The seeds
(10 g) were ground in a Servall Omni-mixer at 15,000 rpm for 3 minutes
in 30 ml of 80% ethanol . The homogenate was filtered, the subsequent
filtrate dried under vacuum and the residue dissolved in 0.1 M tartaric
acid. This aqueous solution was partitioned against ethyl ether and the
ether phase separated and partitioned against an aqueous solution of
0.1 AI sodium bicarbonate. The aqueous bicarbonate phase was acidified
with tartaric acid to pH 2.0 and then partitioned again with 100 ml
ethyl ether. The resulting ether solution was concentrated under nitro-
gen gas. The ether-soluble acidic fraction was subjected to gas chroma-
tography before and after treatment with acetylating agents.
Diazopropane was prepared with slight modification by the method
of Wilcox (112). Briefly, N-propyl-N-nitrosourea ( obtained from Dr.
Merrill Wilcox, Agronomy Department, University of Florida) was reacted
with 40% KOH in water and trapped in peroxide-free ethyl ether. The
etheral solution was stored over sodium sulfate in a polyethylene bottle
in a freezer. To acetylate a sample, sufficient amounts of the solution
were added so that a straw-yellow color persisted at the end of the re-
Alternative esterif ication methods with diazomethane and diazobutane
were used to aid in the identification of aromatic acids. The diazo-
methane reagent was prepared as outlined by Williams (113). Briefly,
N-methyl-N ' -nitro-N' -nitrosoguanidine (Aldrich Chemical Co., Milwaukee)
was added to 20% KOH and trapped in ethyl ether. The diazobutane was
prepared in a manner similar to the diazopropane except substituting N,
X-butyl-N-nitrosourea (obtained from Dr. Merrill Wilcox, Agronomy
Department, University of Florida) for the N-propyl-N-nitrosourea. With
both diazomethane and diazobutane, the initial esterif ication period,
30 minutes, was the same as with diazopropane.
In tests where esterif ication was slow for the carboxyl group or
where acetylation of hydroxyl groups on the ring was slow or non-existent,
0,7% methanolic boron trifluoride was added to these diazo-compounds and
the reaction was allowed to proceed at room temperature for 3 hours.
Standards of chemicals and fractions of extracts were dissolved in
ethyl acetate for gas chromatography. Weights and volume on seed and
solvent fractions were kept so that quantities could be expressed as
seed equivalents. Standards had a final concentration of 1 mg per ml.
Conditions for gas chromatography : Separation of compounds of the
acidic fraction of the ethanol extract was on a model 400 F and M gas
chromatograph equipped with a f lame-ionization detector. The column
consisted of 1/4 inch stainless steel tubing 6 feet long packed with 8%
S.E. 30 on 60-80 mesh Chromosorb W. Helium was used as a carrier gas with
flow rate of 70 ml per minute. Temperatures for the system were as
follows: oven, 180° C; injection port, 260 C; and detector, 250 C,
except as noted in the results.
Identification of extracted compounds was made by comparison of
their retention times with those of the known compounds. Matched reten-
tion times of several derivatives of knowns to those of identically treat-
ed unknowns lent greater support to tentative identification.
Alfalfa bioassay : Peruvian alfalfa seed were separated into red and
yellow seeds. The red seeds were discarded because of their low germina-
tion capability (111) and the yellow seeds were used for the bioassay.
The bioassay was conducted in petri dishes with either filter paper
disks or chromatography paper strips as a moisture holding absorbent,
depending upon the test. Generally 40-50 seeds per dish were used for
each assayed fraction. Before placing the seeds on the moistened paper,
they were soaked in distilled water for a few seconds to improve the
rate of imbibition of the seeds. Once the seeds had been placed in the
dishes, the dishete were placed in the dark at 20° t 2° C. After 24
hours, observations were made on the number of germinated and non-germi-
nated seeds per dish, A seed was considered to have germinated upon
protrusion of the radicle.
Inhibitor characterization : Bioassays were conducted on 80%
ethanolic extracts and fractions paper chromatographed in isopropanol:
ammonia: water (80:1:19, v/v/v) solvent on TOiatman 3 MM chromatography
paper. Chromatograms were divided into sections of 10 R^ units and
assayed, using the alfalfa seed bioassay (18) .
Extracts of peach seeds were also subjected to acid hydrolysis
(pH 2) with acetic acid, alkaline hydrolysis (pH 10) with ammonium
hydroxide, dialysis against distilled water for 24 hours; and heating
for 10 minutes at 50, 75, and 100*-" C. Changes in inhibitory activity
were moiiitored, using the alfalfa bioassay.
Solubility of components of the inhibitor complex in various organic
solvents was investigated. Sections of the paper chromotograms contain-
ing the inhibitory zone were cut into strips representing the equivalent
of a 0.5 g seed sample. These strips were steeped in various solvents
for 2 hours. The solvents were decanted into small petri dishes con-
taining a Wliatman No, 4 filter paper disk and the residue deposited on
the paper by evaporation. Distilled water (1.5 ml) was added to the
petri dishes, and to appropriate controls, and then bioassayed. Redis-
tilled solvents of water, hexane, acetonitrile, ethyl ether, chloroform,
methanol, ethyl acetate and carbon disulfide were used for the solubility
M easurement of benzaldehyde and mandclonitrile : The quantity of
benzaldehyde and raandelonitrile present in seeds under various treat-
ments was determined. All seeds were fully turgid since they were placed
in moist vermiculite for 42 hours at 20° C prior to treatment. Treat-
ment 1 was seeds steeped in 3 x 10 " M thiourea for 6 hours, blotted
and kept in a moist medium until sampled. Treatment 2 was embryos re-
moved from the seed coat and associated tissue after 48 hours from the
start of the experiment. Treatment 3 was the control of intact seeds.
Seeds in each treatment were kept at 20° C and a 4.8 g sample wet
weight, equivalent to approximately 3 g dry weight, were taken at the
following times from the start of seed imbibition: 48, 60, 72, 80, 88,
96, 104, 112, 120, 132, 144, 156, and 168 hours. The samples were
frozen immediately to -70° C and then placed in a freezer at -30° C
until ground, approximately 8 hours. The frozen seeds were ground in a
Wiley mill with a 20-mesh sieve. The mill had been thoroughly cooled by
passing large quantities of dry ice through it before the samples were
ground. Also, sufficient amounts of powdered dry ice were passed
through the mill along with the frozen seeds to keep the grinding head
at approximately the temperature of the dry ice. The ground seeds plus
powdered dry ice were collected together and added to ethyl ether at
-70 C. After the dry ice had sublimed from the ethyl ether (generally
30-40 minutes at room temperature) the solutions were allowed to warm
to approximately -5° C before they were placed in a -30° C environment
for 3 hours. This warming and steeping in a freezer was needed to obtain
benzaldehyde and mandelonitrile in the ether phase. This etheral solu-
tion was subjected to gas chromatography under conditions noted with the
results. Weight and volume were taken quantitatively so the data could
be expressed in the amount of chemical per seed equivalent.
Under the conditions of gas chromatography, benzaldehyde and
mandelonitrile chromatographed as benzaldehyde since heat caused mandelo-
nitrile to decompose to HCN and benzaldehyde. Therefore, the following
series of reactions were used to separate the 2 components. Firstly,
the quantity of both compounds was obtained from gas chromatographic
analysis of an aliquot of an extract. Secondly, the quantity of
mandelonitrile remaining in an etheral solution was determined after
quantitatively removing benzaldehyde by reacting with sodium bisulfite.
This was accomplished by solvent partitioning between the etheral solu-
tion and aqueous 40% sodium bisulfite, Thirdly, quantitative analysis
was again done on the ether phase after 407o potassium cyanide was added
to the aqueous sample layered under ethyl ether and the mixture shaken
vigorously. This converted the sodium bisulfite addition product of
benzaldehyde to mandelonitrile which allowed it to pass back into the
ether phase. After allowing the mixture to stand for 5 minutes in the
cold, the ether phase was subjected to gas chromatographic analysis
the third time. Quantitative determinations were made using the area
under the peak as a measure of both compounds and the peak area of the
sample after addition of sodium bisulfite. The latter represents that
due to mandelonitrile. The difference between the two peak areas was
assumed to be that due to benzaldehyde.
The conversion of benzaldehyde to a sulfite derivative soluble in
water and then conversion to mandelonitrile is a well-knov/n reaction
(26). The sodium bisulfite reacts with the carbonyl group of benz- Ide-
hyde to forni the sulfite addition product. Addition of potassium cyanide
acts as a base and neutralized the sodium bisulfite in equilibrium with
the bisulfite compound to form potassium bisulfite; the simultaneously
liberated benzaldehyde and hydrogen cyanide then combine to give mandelo-
Chilling study : Detemiinations were made of the inhibitor complex
benzaldehyde and mandelonitrile after periods of chilling. Fully turgid
seeds, attaining this condition after 48 hours in moistened vermiculite
at 20° C, were placed at 4° C for 0, 16S, 336, 504, and 672 hours. At
the time of sampling, one sample was removed and extracted immediately
and another sample was placed for an additional 40 hours at 20° C. A
control lot of seeds was maintained at 20 C for sampling at equivalent
times. At each time of sampling, seeds equivalent to 5 g dry weight
were taken in duplicate. The quantity of benzaldehyde and mandeloni-
trile in the seeds was determined as outlined previously and the level
of non-volatile iiihibitors, presumably the beta-inhibitory complex (8),
was assayed as follows. A sample of treated seeds was subjected to
extraction with 807o ethanol after grinding, as previously noted. The
solution was taken to near dryness by vacuum distillation, keeping the
distilling chambei' at less than 5 C. The residue was redissolved in
807o ethanol, applied to chromatographic paper (Whatman 3 MM) and devel-
oped in isopropanol: ammonia; water (80:1:19 v/v/v) solvent, using de-
cending techniques. The inhibitory zone, as determined by Rf, were
sectioned from the chroraatograms, and solutes eluted from the paper with
glass distilled water. The eluates were then diluted in such a way that
equivalent seed weights in the solutions were 1.0 g, 500 mg, 300 mg,
100 mg and mg. The solutions were placed in small petri dishes on
Wliatman No. 4 filter paper disk, frozen and water removed by sublimation
under vacuum. After again moistening the filter pads with 1.5 ml of
H„0, they were bioassayed with the alfalfa bioassay using 40 seeds per
disk. Inhibitory levels were determined by calculations from a dilution
curve based on relative seed weight.
Thiourea and seed coat excision ; The influence of thiourea on
gei'mination of dormant 'Okinawa' peach seed and on anomalous seedling
development is shown in Table 1. It was quite evident from this data
that thiourea greatly increased the per cent germination, but enhanced
anomalous development in the seedlings. In both cases, the higher the
concentration, the greater the effect. The data indicates further that
increases in germination and abnormal growth were statistically signifi-
cant with concentrations of thiourea stronger than 10 M.
In determining the possible interaction between thiourea and seed
coat on germination and subsequent seedling growth, the most striking
finding was the absence of abnormal seedlings in any of the treatments;
yet very good germination was obtained, as shown in Table 2. The length
of time after imbibition and thiourea treatment for embryo excision
seemed to have little effect on germination.
Influence of Benzaldehyde, cyanide, and mandelonitrile on seed
germination ; The data in Table 3 indicates that cyanide does not dras-
tically reduce germination, except in very high concentrations (1.0 M) .
Data taken 20 days after start of imbibition showed that the 1.0 M con-
centration was still significantly different from the lower concentra-
tions used. No abnormalities were noted in the seedlings from any of
the tx-eatments, and, interestingly, the 1.0 M cyanide did not kill the
Table 1. — Influence of thiourea concentrations on germination and
per cent of production of abnormal seedlings from
'Okinawa' peach seeds.
% abnormal'' '
3 X 10
^Each treatment was replicated 3 times with 40 seed per replication.
^Means not having a following letter in common are significantly differ-
ent at the 1% level.
"Percentage based on the total number of seed germinated.
Table 2. — Effect of thiourea concentration and embryo excision on
germination of 'Okinawa' peach seeds 12 days after start
of imbibition and on abnormal seedling production 32
days after start of imbibition.
Chemical Seed coat % germination^ % atypical seedling
Excised; 42 hrs
Excised; 42 hrs
120 hrs 100.0
3 X 10"%
Excised; 42 hrs
^Seeds were imbibed 42 hours, then treated with chemicals for 6 hours
^Each treatment consisted of 3 replications of 9 seed each.
^Means not having a following letter in common are significantly differ-
ent at the 1% level.
^Hours after start of imbibition.
Table 3. — Per cent germination of 'Okinawa' peach seeds 7 and 20 days
after start of imbibition as influenced by cyanide^.
3 X 10
88. 9 b
^Seeds were imbibed for 42 hours, then treated with the designated
cyanide concentrations for 6 hours.
Each concentration consisted of 3 replications with 6 seed per
"Means not having a following letter in common are significantly
different at the 57o level.
The treating of samples of excised embryos with various concentra-
tions of mandelonitrile and benzaldehyde resulted in the inhibition of
germination with some of the stronger concentrations (Tables 4 and 5) .
Mandelonitrile at 1.4 to 140.0 mg/g completely inhibited germination,
while all other concentrations except 0.42 mg/g inhibited only slightly.
Data taken 5 days after removing the seeds from the chemical shov;ed
that 1.4 mg/g exhibited very little inhibitory influence. Concentrations
of 4.2 to 140.0 mg/g were still strongly inhibitory (Table 4). Concen-
trations of benzaldehyde of 11.0 and 110.0 mg/g completely inhibited
germination, while a concentration of 3.3 mg/g resulted in only 16.77o
germination. Concentrations lower than 3.3 mg/g had no measurable in-
fluence (Table 5). Five days after removal of seeds from the benzaldehyde
media, germination occurred to an appreciable extent in the 3.3 mg/g
treatment but 11.0 and 110.0 mg/g were still inhibitory. As found with
cyanide, the anomalous growth patterns were not present on seedlings
produced from seeds treated with either mandelonitrile or benzaldehyde.
The influence of the benzaldehyde and mandelonitrile on seed germination
is portrayed graphically in Figure 1.
Aromatic acids investigation ; Tentative identification of the com-
ponents isolated from the propyl esters of the acidic fraction of an
ethanol extract of peach seeds was made by comparing the retention times
on gas chromatograms with those of known compounds. A gas chromatogram
of the fractions is shown in Figure 2.
The phenolic compounds tentatively identified were benzoic, mandelic,
o-hydroxycinnamic, 2, 6-dihydroxybenzoic, o-hydroxybenzoic, p-hydroxyben-
zoic and 2,4-dimethoxybenzoic acids (Table 6), The gas chromatograms of
the standards for the known compounds listed above can be found in the
Table 4. — Per ceiit germination of 'Okinawa' peach seeds 7 and 12 days
after start of imbibition as influenced by mandelonitrile^'^.
Mean % germination
mg/g of perlite
140.0 0.0 a 0.0 a
14.0 0.0a 0.0a
4.2 0.0 a 0.0 a
1.4 0.0 a 83.3 b
0.42 100.0 c 100.0 c
0.14 94.4 be 100.0 c
0.042 ■' 94.4 be 100.0 c
0.014 94.4 be 100.0 c
Control 88.9 b 88.9 be
Seeds were allowed to imbibe for 2 days, then placed in perlite
containing mandelonitrile for 5 days. The indicated quantity of
mandelonitrile was applied to the perlite.
^Each treatment was replicated 3 times with 6 seed per replication.
^Means not having a following letter in common are significantly
different at the 1% level.
Table 5. — Per cent germination of 'Okinawa' peach seeds 7 and 12 days
after start of imbibition as influenced by benzaldehyde'^' y.
Benzaldehyde Mean % germination^
mg/g of perlite 7 days 12 days
110.0 0.0 a 0.0 a
11.0 0.0 a 0.0 a
3.3 16.7 b 94.4 b
1,1 100.0 c 100.0 c
0.33 100.0 c 100.0 c
0.11 • 100.0 c 100.0 c
0.033 100.0 c 100.0 c
0.011 100.0 c 100.0 c
Control 100.0 c 100.0 c
Seeds were allowed to imbibe for 2 days, then placed in perlite contain-
ing benzaldehyde for 5 days. The indicated quantity of benzaldehyde
was applied to the perlite.
^Each treatment was replicated 3 times with 6 seed per replication,
Means not having a following letter in common are significantly
different at the 1% level.
c: « ^
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o ^ o
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O CO S
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i-l -H &-<
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ci cX _•
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s ■*-> o
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8 16 24 32
Gas chroraatogram of the propyl esters of the acidic
fraction from an ethanol extract of peach seeds.
Time is in minutes. (See Table 6 for gas chromato-
Table 6. — Relative retention time and possible identity of components
separated by gas chromatography of the propyl esters of the
acidic fraction from an ethanolic extract of peach seeds^.
Relative retention timc'^
Possible identity of acids''
Malic or mandelic?
- Instrument ; F &. M model 400, flame detector.
Column ; 87o S.E. 30 on 60-80 mesh chromasorb W, acid washed,
silane treated; 1/4" 0,D. stainless steel 6' in length.
Carrier gas ; He. Outlet flow rate ; 70 ml/min.
Oven temp; 180° C. Injection port temp; 260° C.
Detector temp ; 250° C.
Range and attenuation ; 10 x 8. Chart speed ; 1/4" per rain.
- Relative retention time is based on benzoic acid.
Possible identity based on matched retention times,
Inhibitor chai-acterization ; Using the Peruvian alfalfa bioassay,
it was found that extraction of 8 g wet weight of dormant peach seeds
with 80% ethanol yielded a strongly inhibitory complex (0% germination).
Specific gravity measurements indicated that the inhibitory influence
was due to factors other than osmotic ones. Paper chromatography of the
ethanol extract, using an isopropanol: ammonia: water (80:1:19 v/v/v)
solvent system, yielded a strong inhibitory complex between R^ ' s 0.6 and
0.8 when bioassayed with the alfalfa seed test (Table 7).
From tests on the influence of acids, bases and heat on the stabil-
ity of the inhibitory complex, the data on per cent germination from the
alfalfa bioassays (Table 8) would seem to indicate that the inhibitory
complex was reasonably stable since none of the treatments destroyed the
inhibitory capacity of the extract.
Comparison of various organic solvents (Table 9) for the solubil-
ization of the inhibitory complex showed that the more polar solvents
(water and alcohol) serve as suitable solvents for the inhibitor. The
data indicated also that the inhibitor may be only partially soluble
Isolation and characterization of benzaldehyde and mandelonitrile
from peach seeds : Benzaldehyde and mandelonitrile were isolated and
characterized from peach seeds by several techniques. Crushed peach
seeds evolve an aroma similar to that of benzaldehyde and mandelonitrile.
Co-chromatography of the pure chemicals and the extract components from
peach seeds by chromatography yielded identical R „ ' s and retention times,
respectively. Ultra-violet fluorescence (3200 A° and 2537 A°) of benz-
aldehyde and a fraction from an ethanol extract from peach seeds on
paper chromatograms were identical. Also, benzaldehyde and the extracted
Table 7. — Paper chromatographic separation of the
inhibitory complex from dormant peach
Rf Value-^ % Germination^
0,0 - 0,1 92,5
0.4 - 0.5 55,0
0,5 - 0,6 0,0
0.6 - 0,7 0,0
0.7 - 0,8 0.0
0,9 - 1.0 80.0
^Solvent system: Isopropanol: ammonia: water
(80:1:19 v/v/v) .
^Bioassayed with the alfalfa seed test.
Control = 90%.
Table 8. — Influence of acids, bases and heat on the
inhibitory complex from peach seeds after
Test % Germination^
Acid hydrolysis (pH 2) 0.0
Alkaline hydrolysis (pH 10) 0.0
Dialysis, inside tubing 0.0
outside tubing 0.0
Heating for 10 minutes:
50° C 0.0
75° C 0.0
100° C 0.0
Extract control 0,0
Water control 90.0
Bioassayed with the alfalfa seed test. Seed
equivalent of the extract was 0.5 g dry weight,
Dialysis was conducted with seamless cellulose
tubing against distilled water for 24 hours.
Table 9. — Solubility of the inhibitor-complex in
various organic solvents as determined
by the alfalfa bioassay.
^Elution fraction from chromatogram section of R^ 0.6-
^Chromatogram section containing the inhibitory complex
after eluting with the respective solvent.
component reacted similarly to aldehyde indicators. Component of an
ethanol extract and benzaldehyde formed a sodium bisulfite addition
product which then generated mandelonitrile on treatment with KCN.
Ultra-violet fluorescence (3200 A° and 2537 A°) of mandelonitrile
and a fraction from an ethanol extract from peach seeds on paper chroma-
tograms were identical. The extract components and mandelonitrile form
benzaldehyde and cyanide when subjected to high temperatures (200-250° C) ,
Mandelonitrile and components of the extract reacted alike when tested
with hydrocyanin indicators.
Quantitative detemiinations of benzaldehyde and mandelonitrile :
Benzaldehyde and mandelonitrile were determined using procedures estab-
lished in identifying the 2 compounds. Briefly, this was gas chromatog-
raphic analysis of the ethereal extract before making a sodium bisulfite-
addition product, after the reaction to assay the level of decrease and
again after converting the benzaldehyde to mandelonitrile by KCN. A
chromatogram of the composite of both compounds is shown in Figure 3a.
After treating with sodium bisulfite, the peak is reduced (Figure 3b)
and increased after the subsequent addition of potassium cyanide
(Figure 3c) .
Comparison of the influence of thiourea treatment, and embryo exci-
sion, as compared to a non-germinating control of intact seeds, on the
rate of release of benzaldehyde and mandelonitrile both collectively and
individually is shown in Figures 4, 5 and 6, The graphs indicated that
intact seeds and thiourea-treated seeds had peak times of production of
benzaldehyde and mandelonitrile at about the same time, 72 hours, while
the excised seeds had a delay in the maximum period of production by 16
hours. The thiourea-treated seeds had a second peak of production at
Fig. 3. Gas chromatograms of a known composite sample of an etheral
solution of benzaldehyde-mandelonitrile: (a) initial solution;
(b) after addition of a solution of sodium bisulfite; and (c)
after addition of potassium cyanide.
Gas chromatograph parameters.
Carrier gas :
F &, M model 400, flame detector.
8% S.E. 30 on 60-80 mesh Chromosorb W, acid-
washed, silane treated; 1/4" 0,D. stainless
steel 6' in length.
Helium. Outlet flow rate : 70 ml/min.
Oven, 100° C; Injection port, 150° C; Detector,
10 X 8
1/4" per minute.
H- q: Lli
^ H- LU
pGGS Ajp 6/6uu
P99S Ajp B/Buu
pGQS Ajp 5/6uj
120 hours after the start of imbibition. Relatively larger amounts of
mandelonitrile than benzaldehyde were in the extracts from the seeds.
The effect of the 3 treatments on peach seed germination is shown
in Figure 7. The excised seeds attained 100% germination at approxi-
mately 132 hours or about 44 hours after the peak in production of benz-
aldehyde and mandelonitrile. However, those seeds treated with thiourea
required a much longer period of time after the peak production time in
order to attain nearly 1007o germination. This was true even when the
time from the second peak at 120 hours was considered.
Quantitative determination of benzaldehyde, mandelonitrile and the
inhibitory complex of seeds subjected to various degrees of chilling :
Gas chromatographic determination of the quantities of benzaldehyde and
mandelonitrile in peach seeds at weekly intervals during the chilling
period indicated only trace amounts were present. Calculations indicated
that the tissue level of both chemicals ,was below 1.0 ug/gra dry weight
of tissue. Only trace amounts of benzaldehyde and mandelonitrile were
detected by gas chromatography on seeds placed at 20° C for 40 hours
after removal from various intervals of chilling.
The level of the 80% ethanol soluble inhibitory complex of peach
seeds, as determined by the alfalfa bioassay, does not decrease during
the chilling period (Figure 8) . Slight week-to-week fluctuations were
present but the overall analysis showed little change in the level.
However, the per cent germination of seed periodically removed from the
chilling temperatures and placed at 20° C indicated that 504 hours of
chilling was sufficient to terminate dormancy in over 807o (Figure 9) of
the population of the seeds. • 'i
o o — o
o — o o
-I , ^-
Fig, 7, Germination of peach seed as influenced by embryo excision,
and thiourea treatments as detennined periodically after the
start of imbibition, (Growth of excised embryos was taken
to be equivalent to germination when the radicle had elongated
to 2 mm. )
Fig. 8. Relative inhibitory activity, as measured by the alfalfa
bioassay, of the inhibitory complex in an ethanolic extract
of peach seeds chromatographing between R^ ' s 0.6 to 0.8.
(Hours of chilling were just prior to extraction; and seed
equivalents were A= 1.0 g. B= 0.5 g, C= 0.3 g, D= 0.1 g and
E= control . )
Hours of chilling
Fig. 9. Germination of peach seeds as influenced by 5 C of varying
Influence of chemicals on possible stimulation of peach seed germi -
nation : The influence of benzaldehyde, mandelonitrile, benzoic acid and
p-hydroxybenzoic acid on the breaking of seed dormancy was determined
and the test differed from that for inhibition of germination in that
they were applied to intact seeds. Using benzaldehyde and mandelonitrile
at various concentrations, there was no evidence for a stimulatory effect
on seed germination (Table 10). However, the 2 chemicals were active
in inhibiting the weak capacity for germination, which supported the
data of an inhibitory influence as shown earlier.
Benzoic and p-hydroxybenzoic acids were used on intact seed at
concentrations ranging from 10 to 10 M. The data in Table 11 in-
dicates that p-hydroxybenzoic acid at 10 and 3 x 10 M may have
slightly stimulated seed germination as compared to the control; yet
this is of doubtful significance since the control had a weak capacity
to germinate (compare Tables 10 and 11). Benzoic acid had little in-
fluence on germination under the conditions of these tests.
L-mandelic and p-hydroxybenzoic acid determinations : Gas chroma-
tograms of the control, peach seed extract, L-mandelic acid and p-hy-
droxybenzoic acid after treating with diazomethane for 30 minutes are
shown in Figures 10, 11, and 12. These should be primarily the esiors
of the aromatic acids. These were separated on the gas chromatograph
at an oven temperature of 180° C. The methoxy and butoxy esters were
separated by gas chromatography after acetylation by diazomethane and
diazobutane, respectively. Since those derivatives were more volatile,
an oven temperature of 150° C was used.
Based upon the comparison of retention times of the components in
the extract with those of the standards (Table 12), it was concluded
Table 10. — Mean per cent germination of dormant 'Okinawa'
peach seeds 30 days after start of imbibition
as influenced by benzaldehyde and mandelo-
Concentration, M^ Benzaldehyde^ Mandelonitrile^
1.0 0,0 a 0.0 a
10 0.0 a 0.0 a
3 X 10~ 16.7 b 0.0 a
10 22.2 b 38.9 b
33.4 b 33.4 b
Seeds were imbibed for 2 days, then exposed to chemical
concentrations for 5 days.
^Each treatment was replicated 3 times with 6 seed per
Means not having a following letter in common were
significantly different at the 5% level.
Table 11. — Mean per cent germination of dormant 'Okinawa'
peach seeds 30 days after start of imbibition
as influenced by benzoic and p-hydroxybenzoic
Concentration, My Benzoic^ p-Hydroxybenzoic
lO"-"- 5,5 a 38.9 b
3 X 10"^ 0.0 a 38.9 b
lO"^ 16.7 a 11.2 a
10""^ 16.7 a 11.2 a
16.7 a 16.7 a
'^Seeds were in moist medium for 2 days, then exposed to
chemical concentrations for 5 days.
^Each treatment was replicated 3 times with 6 seed per
^Means not having a following letter in common are
significantly different at the 5% level.
Fig. 10. Gas chromatogram of diazomethane-solvent control. Retention
time is in minutes. (See Table 6 for parameters of gas
chromatograph , )
4 8 12
Fig. 11. Gas chromatograms of L-mandelic acid(a) and
p-hydroxybenzoic acid(b) treated for 30 minutes
with diazomethane. Retention time is in minutes.
(See Table 6 for parameters of gas chromatograph. )
Fig. 12. Gas chromatogram of an ethanol extract from peach seeds treated
for 30 minutes with diazomethane. Retention time is in minutes.
(See Table 6 for parameters of gas chromatograph. ) (M=
L-mandelic acid and pHBA= p-hydroxybenzoic acid.)
Table 12. — Comparison of retention times of p-hydroxybenzoic
acid and L-mandelic acid as influenced by various
Retention times (minutes)
1-diazomethane, 30 minutes;
2-diazomethane, 3 hours:
3-diazobutane, 3 hours:
^Refer to Materials and Methods for the details of each
that L-mandelic acid and p-hydroxybenzoic acid were present in peach
seeds after 48 hours' imbibition. However, only trace amounts of L-
mandelic acid could be detected in the extract (Table 13). On the other
hand, sufficient quantities of p-hydroxybenzoic acid were present for an
estimation of amounts in the tissue. Based on peak area comparison of
components of the extract with the standard, it was estimated that ap-
proximately 0.12 ug of p-hydroxybenzoic acid was present in 1 g wet
weight of seed tissue under the conditions of the tests.
Table 13. — Comparison of peak areas of p-hydroxybenzoic
acid and L-mandelic acid as influenced by
various acetylation procedures.
Peak area, mm
1-diazomethane, 30 minutes!
2-diazoraethane, 3 hours:
Approx . 5.0
3-diazobutane, 3 hours:
Refer to Materials and Methods for the details of each
^Each standard represents 2 ug of the respective compound.
A quantitative method was devised to determine the amount of benz-
aldehyde and raandelonitrile in peach seeds. The method was designed to
quantitatively obtain the 2 volatile components in an ethereal solution
so it could be analyzed by gas chromatography. Grinding of the frozen
tissue and extraction at a low temperature prevented enzymatic release
and destruction of benzaldehyde and mandelonitrile. Keeping the ethereal
solution cool and immediate analysis prevented loss by volatilization.
Also, the analysis by gas chromatograph was done before and after reac-
tion with aqueous sodium bisulfite and again after reacting the benz-
aldehyde-sulf ite addition product with potassium cyanide to form mandelo-
nitrile. The chemical reactions used are well known (26), and the deter-
mination of pure benzaldehyde and mandelonitrile by the technique de-
scribed was shown to be quantitative.
Using this procedure, the quantity and rate of release of mandelo-
nitrile and benzaldehyde were studied in relation to germination. The
data indicated that a lag time existed in excised seeds for the maximum
release of mandelonitrile and benzaldehyde. The intact seeds and those
treated with thiourea differed only in magnitude and the thiourea-treated
seeds exhibited a secondary peak at 120 hours.
The maximum period of gemiination of the excised seeds was about
48 hours after the maximum period of release of benzaldehyde and mandelo-
nitrile whereas the greatest period of germination of seeds treated with
thiourea occurred about 160 hours after the second peak of release of
benzaldehyde and mandelonitrile. Thus, there was no indication that
either benzaldehyde or mandelonitrile was correlated with an inhibition
of germination under conditions of these tests. Yet, when concentrations
of benzaldehyde and mandelonitrile are present in tissues at concentra-
tions of 11.0 and 4.2 mg/g respectively, they would be affecting the
system. Thus, the 2 compounds may have a temporary influence on germi-
nation, and it could be possible under certain circumstances a factor
contributing to dormancy.
Determinations were also made of the content of mandelonitrile and
benzaldehyde present in peach seeds at weekly intervals during chilling.
Only trace amounts were observed at the various times of sampling. Thus,
it seems that the majority of mandelonitrile and benzaldehyde was re-
leased between about 72 and 96 hours after the start of imbibition.
This was the first reported instance of the detection and measure-
ment of mandelonitrile in peach seeds. It may be significant that the
quantity of mandelonitrile present was much greater than that of benz-
aldehyde. This would indicate that the hydrolysis of amygdalin in in-
tact seeds was not the same as in seed homogenates. In the latter case
the products formed are benzaldehyde and cyanide with the mandelonitrile
considered an unstable intermediate (104).
Interest was also directed at the presence of phenolic acids in
peach seeds. Using gas chromatographic techniques, benzoic, o-hydroxy-
cinnamic, 2, 6-dihydroxybenzoic, o-hydroxybenzoic, p-hydroxybcnzoic,
2,4-dimethoxybenzoic and mandelic acids were isolated and tentatively
identified. Of primary interest was p-hydroxybenzoic acid since it had
been reported in the literature as having growth regulator actions (105).
With this in mind, it was necessary to determine if p-hydroxybenzoic acid
existed in peach seeds. Using extraction procedure for phenolic acids
(113), gas chromatographic analysis of various derivatives were made of
the extracted components. Positive identification was made for p-hydrox-
ybenzoic and a strong indication was noted that L-mandelic acid was
present in the seeds. The latter has been reported to occur in peach
seeds (R. H. Biggs, Unpublished data), and found to inhibit germination
of alfalfa seeds at 10~° M concentrations. Jones and Enzie (46) identi-
fied a growth-inhibiting substance from peach flower buds as being
Since degradation products of amygdalin were found to occur in
seeds, attempts were made to assess the influence of cyanide, benzalde-
hyde and mandelonitrile on germination. Cyanide treatments indicated
that only at the highest concentration tested, 1.0 M, was an inhibitory
influence shown. Recently, it has been reported that some plants, par-
ticularly Vicia sp., have the capability of metabolizing cyanide and
converting it into non-toxic compounds (34, 69). It was observed that
hydrogen cyanide (■'■'^C) was incorporated into asparagine in a number of
plant species. This was thought to be accomplished by cyanide coupling
with serine directly to form the 4-carbon chain of beta-cyanoalanine.
The beta-cyanoalanine could then form asparagine, or by addition of a
gamma-glutamyl group, form gamma-glutamyl-beta-cyanoalanine. It was
concluded that cyanide had little influence on germination, except at
concentrations considered quite high. Interestingly, this indicates
that peach seed do contain a cyanide-resistant mechanism for respiration.
Furthermore, the subsequent seedlings were much greener and exhibited
other characteristics that accompany nitrogen fertilization. Thus, it
was concluded that the tissues were incorporating cyanide.
In contrast to the results of cyanide treatments, concentrations of
4.2 mg/g mandelonitrile and 11.0 mg/g benzaldehyde completely inhibited
germination of excised embryos. It was noted that mandelonitrile in-
hibited at a weaker concentration and that the intermediate concentra-
tion of both compounds had an action that was reversible. Thus, if high
enough concentrations of benzaldehyde or mandelonitrile did occur in
seeds they could be inhibitory and the action could be transitory if the
compounds were subsequently degraded (104).
The possibility that subsequent derivatives of benzaldehyde could
be involved in seed germination was investigated. Thus, the influence
of benzoic and p-hydroxybenzoic acids on dormant peach seeds was tested.
Benzoic acid had little influence, but concentrations of p-hydroxybenzoic
acid at 3 X 10"^ and 10~ M significantly increased the degree of germi-
nation as compared to the control.
The fact that p-hydroxybenzoic acid has been found to have growth
regulatory properties (105) and its presence in peach seeds suggested
that it may play a role in dormancy. The growth regulatory activity of
p-hydroxybenzoic acid has been established for woody cuttings of Ribes
rubrum (105). Pilet (78) has reported that p-hydroxybenzoic acid at
low concentrations causes a stimulation of the growth of stem sections,
while at high concentrations it inhibits growth. The inhibition was
apparently due to the stimulation of lAA-oxidase and subsequent decrease
in auxin level (116). Also, the activation observed for lower concentra-
tions of p-hydroxybenzoic acid indicated that it acted on several other
biochemical processes which were connected with growth (78).
In Ribes rubrum , p-hydroxybenzoic acid was present in the range of
0.2 - 1.0 ug/g of fresh tissue (105). The quantity found in peach seeds
was approximately 0.12 ug/g of fresh tissue. Thus it appears that the
tissue-levels of p-hydroxybenzoic acid in both dormant Ribes woody stems
and dormant peach seeds were similar. In the case of Lens stems, inter-
node sections were stimulated to elongate at 10~ M concentration (78).
At higher concentrations, the growth of stem sections was inhibited.
The quantity isolated from peach seeds was in the range that was inhibi-
tory in the Lens bioassay. Thus, it could be inhibitory to the seeds.
However the data was such with peach seeds that this point can be con-
sidered a matter of conjectual. Yet, it was shown that p-hydroxybenzoic
acid would stimulate peach seed germination at 3 x 10 to 10 M con-
centration. This stimulation was from adding p-hydroxybenzoic acid to
the external media for 120 hours. Thus, the internal concentration could
have been much lower. The bioassay would not demonstrate an inhibitory
The ethanolic extracted inhibitory-complex obtained from peach
seeds was studied with the use of paper chromatography and other physical
treatments in order to obtain some clues as to its identity. The R^
values obtained on paper chromatography correspond with the inhibitory
area obtained by Bennet-Clark and Kefford (8) using the same solvent
with an alcoholic extract from Ribes sp. This inhibitory area was termed
the beta-inhibitor complex. Recently, the beta-inhibitor concentrated
from an acidic fraction from extracts of dormant maple buds was thought
to be a complex of phenolic substances (86) . However, the phenolic com-
pounds described were found not to be identical with any of the phenolic
compound previously proposed as being members of the beta-inhibitor
complex. Recently, many of the phenolic compounds associated with the
beta-inhibitor complex have been identified. Koves and Varga (53) re-
ported the identification of many phenolic compounds, among which were
several of the hydroxybenzoic acids.
The data on the level of the inhibitor-complex during the chilling
period showed that it did not change drastically. In fact, at the end
of chilling period, the level seemed to be greater than anytime during
chilling. This finding was in line with that found by Villiers and
Wareing (106, 107) for dormant organs of Fraxinus excelsior . Briefly,
chilling has no effect on the level of inhibitors in the tissue but ter-
mination of dormancy was accompanied by a buildup in growth promotors in
the seed. This may be the case for peach seeds since the capacity to
germinate increased with increases in the duration of the chilling period.
The products of amygdalin degradation, mandelonitrile, benzaldehyde
and cyanide do not appear to directly influence the breaking of peach
seed dormancy. However, it would seem that a hydroxylated derivative,
p-hydroxybenzoic acid, of the benzaldehyde oxidation product, benzoic
acid, exhibits some stimulatory influence upon dormant peach seeds.
Furthermore, L-mandelic acid, as well as other phenolic compounds, may
be involved in peach seed dormancy.
The induction of germination of peach seed by thiourea substantiated
previous reports that this chemical will terminate seed dormancy (76,
97). Furthermore, it supported earlier observations (30, 80) that the
growth of the subsequent seedlings was not abnormal if the proper envi-
ronmental condition were maintained during germination.
SUMMARY AND CONCLUSIONS
Investigations were initiated to determine the relation of certain
phenolic compounds to peach seed germination. The phenolic compounds
of primary interest were those which are degradation products of the
glucoside, amygdalin, namely, mandelonitrile and benzaldehyde, and their
immediate by-products. The following conclusions were made based on the
1. Mandelonitrile and benzaldehyde at 1.4 to 11.0 mg/g of perlite
inhibited germination of excised embryos, but did not stimulate dormant
seeds to germinate. Quantitative determinations of these 2 compounds
from peach seeds by gas chromatography indicated that the majority of the
mandelonitrile and benzaldehyde was released between 72 and 96 hours
after the start of imbibition and thereafter only trace amounts could be
observed. Only at this time was the tissue-level high enough to be con-
sidered inhibitory to germination, yet it showed no correlation with
germination. Furthermore, determinations made at weekly intervals during
chilling indicated that only trace amounts were present at any of the
sampling times during chilling. Therefore, it was concluded that mandelo-
nitrile and benzaldehyde have no direct, inhibitory or promotive influ-
ence on the germination of peach seeds.
Cyanide had little effect on reducing the per cent germination at
concentrations less than 1.0 M. From observations on the increased size
of seedlings in several cyanide treatments, it was postulated that the
tissues were incorporating cyanide, however no measurements of the in-
crease in glucoside content was made.
2. The fact that phenolic acids could be produced in dormant peach
seeds as a result of the metabolism of mandelonitrile and benzaldehyde,
led to an investigation of phenolic acids in dormant peach seeds, and
several phenolic acids, including the hydroxy and methoxy derivatives of
benzoic acid, were found. Of prime interest was the finding that p-hydrox-
ybenzoic acid at concentrations of 3 x 10"^ to lO"-"" M would slightly stim-
ulate the germination of dormant peach seeds.. However, quantitative de-
terminations showed that approximately 0.12 ug of p-hydroxybenzoic acid
was present per 1.0 g of tissue on a wet weight basis which was below
that found to be necessary in the external media for germination. Deter-
minations of the tissue-levels of p-hydroxybenzoic acid in germinated
seed was not conducted. L-mandelic acid, a product of mandelonitrile
hydrolysis, was also shown to be present in amounts in the range of 0.005
to 0.05 ug/g of fresh tissue. The influence of L-mandelic acid on peach
seed germination was not studied.
3. The inhibitor-complex level of peach seeds which appeared on
paper chromatograms at an R^ of 0.6 - 0.8 was found to be essentially the
same after chilling as prior to chilling. Thus this complex does not
appear to be involved in the maintenance of dormancy of peach seeds.
The inhibitory-complex had similar characteristics to the beta-inhibitor
complex reported to be found in other plant tissues.
4. Experiments with thiourea supported previous research and showed
that the time of embryo removal from the seed coat and associative tissue
after seed imbibition had little influence on the amount of abnormal
APPENDIX: GAS CHROMATOGRAMS OF STANDARDS
Fig. 13. Gas chromatograms of the propyl esters of benzoic
acicl(a) and mandelic acid(b). Retention time in
minutes. (See Table 6 for parameters of gas
chromatograph . )
Gas Ghroinatogi*ai.is ei the propyl ggtoi'g of o-liydroxybenseie
acid(a) and p-hydroxyboHKoio acid(b). Retention time in
minutes. (See Table 6 for parameters of gats ehromatogi-aph. )
Fig. 15. Gas chromatograms of the propyl ester of
2, 6-dihydroxybenzoic acid. Retention time
in minutes. (See Table 6 for parameters
of gas chromatograph . )
4 8 12 16
Fig, 16. Gas chromatograms of the propyl ester of
2,4-dimethoxybenzoic acid. Retention time
in minutes. (See Table 6 for parameters of
gas chromatograph, )
4 8 12
Fig. 17, Gas chromatograms of the propyl ester of
o-hydroxycinnamic acid. Retention time
in minutes. (See Table 6 for parameters
of gas chromatograph. )
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The author, James Bruce Aitken, was born August 1, 1938, in Orlando,
Florida. He received his secondary education at the Lakeview High School
in Winter Garden, Florida between the years of 1953 and 1956. He at-
tended Clemson University in Clerason, South Carolina and was granted the
degree of Bachelor of Science with major in Agriculture in January, 1962
and was also granted the degree of Master of Science with major in
Horticulture from Clemson University in January, 1964.
In 1964, he was granted an assistantship from the Department of
Fruit Crops, University of Florida to study toward the degree of Doctor
of Philosophy. He entered the University of Florida in April, 1964, and
completed his work towards the degree of Doctor of Philosophy in August
He is a member of Alpha Zeta, Phi Sigma and Gamma Sigma Delta hon-
orary fraternities. He is also a member of the American Association for
the Advancement of Science, and The American Society for Horticultural
He is married to the former Patricia Ann Dillard and they have one
This dissertation was prepared under the direction of the chairman
of the candidate's supervisory conunittee and has been approved by all
niembers of that conuiiittee. It was submitted to the Dean of the College
of Agriculture and to the Graduate Council, and was approved as partial
fulfillment of the requirements for the degree of Doctor of Philosophy.
Dean, College of Agriculture
Dean. Graduate School