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The seeds of loblolly pine (Pinus taeda L.) were cold-stratified for 0, 14, 28, 42, and 56 days. Endogenous growth regulators were extracted from these seeds, and also from the germinating and the 28-day warm stratified seeds. Partially purified extracts were separated on chromatographic paper. The chromatograms were cut into 10 equal segments, and these were tested for biological activity using three different bioassays. The results indicated that the unstratified seeds and those stratified up to a period of 28 days contained very little or no growth promoter (GA-like substances), and a relatively high concentration of an inhibitor (presumably abscisic acid). Following 42-day stratification, the promoter concentration gradually increased while the inhibitor level fell almost to zero. A high level of promoter but no inhibitor was detected in germinating seeds. No auxin-like activity was noted in the unstratified seeds. This activity slowly increased up to a period of 28 days and remained at this level for the subsequent stratification periods. However, the activity greatly increased in the germinating seeds. Very little changes in the levels of growth regulators were noted in warm-stratified seeds as compared to the unstratified controls. [ABSTRACT FROM AUTHOR]

An inhibitor from Pinus radiata was separated using paper chromatography from an acidic ether fraction of a stem tissue extract. Using electrophoresis the inhibitory activity was resolved into two parts. One part remained at the origin. The second part behaved similarly to ABA, in electrophoresis and was investigated further. The inhibitor has similar properties to ABA in electrophoresis; TLC using a number of solvent systems; UV fluorescence spectra: UV absorption; ORD spectra and gas chromatography. Final proof of the identity of the natural inhibitor as ABA was obtained by gas chromatography-mass spectrometry. [ABSTRACT FROM AUTHOR]

The wheat coleoptile elongation bioassay was used for determination of growth-promoting and growth-inhibiting substances in avocado (Persea americana Mill.) fruit tissues, during development and maturation. Growth-promoting activity was found in two zones on paper chromatograms developed with isopropanol : ammonia : water (10:1:1 v/v): Rf 0.30-0.50 and Rf 0.8-0.9. Growth inhibiting activity was found in three different zones: "A" Rf 0.0-0.2, "B" (abscisic acid) Rf 0.6-0.8, and "C" (l-acetoxy-2,4-dihyroxy-n-heptadeca-16-ene) Rf 0.85-1.0. Higher levels of auxins were found in seed tissues than in the mesocarp. No correlation was found between fruit growth rate and level of extractable auxins in the mesocarp. The amount of abscisic acid (ABA) in the mesocarp was constant during fruit growth. A gradual and consistent increase in l-acetoxy-2,4-dihydroxy-n-hepta-deca-16-ene was found during fruit growth, reaching a maximum when the fruit attained maturity. [ABSTRACT FROM AUTHOR]

A comparative study of the level of abscisic acid (ABA) and cytokinin and of ethylene production by rose (Rosa sp.) petals of the short-lived cultivar Golden Wave (Dr. Verhage) and the long-lived cultivar Lovita was conducted. In both cultivars, the level of ABA increased as the flowers aged; it was higher in Golden Wave in all developmental stages tested. Ethylene production by cut flowers of the two cultivars remained low for a short time concomitant with development and then increased sharply. The rise in ethylene production occurred after 3 and 4 days in Golden Wave and Lovita, respectively. Cytokinin level increased as the flower started to open and then decreased to a low level. The significance of these changes in relation to maturation and senescence of rose petals is discussed. [ABSTRACT FROM AUTHOR]

The growth-inhibiting effect of inhibitor β, extracted from the potato variety Majestic, was compared with the effect of abscisic acid by means of the Avena coleoptile straight-growth test. Dose-response curves showed that total growth inhibition is attained by inhibitor β, but this is never caused by abscisic acid even in high unphysiological doses. By chromatographic methods inhibitor β can be separated into three active components. One of these is a phenolic substance with weak growth-inhibiting effect. The two others contribute equally to the inhibitory effect, and one of them is probably abscisic acid. Beside these inhibiting substances there are components without inhibitory effect, many of phenolic character, included in the inhibitor β complex. [ABSTRACT FROM AUTHOR]

Indol-3yl-acetic acid (IAA) was identified in Phaseolus vulgaris L. Shoot tissue of seedlings, exposed to light for 5 days, had a higher level of IAA than etiolated seedlings of the same age. The content of IAA increased in green seedlings during light treatment for 5-12 days. No increase could be measured in dark-grown seedlings. Inhibitory substances appeared at different Rf-values. The main part was identical to the inhibitor-β complex and occurred in a higher amount in light-grown seedlings than in etiolated taller ones. One part of the inhibitor-complex appeared to be abscisic acid (ABA). It is suggested that both IAA and acid inhibitors may play an important role in the control of stem growth and differentiation, although light effects on other hormones and regulatory systems cannot be ignored. [ABSTRACT FROM AUTHOR]

Young plants of the wilty tomato mutant, flacea, in which the stomata resist closure, were sprayed with abscisic acid eight times over a period of 24 hours in light and darkness. The hormone induced closure of stomata similarly in leaves treated either in light or in darkness. Abscisic add does not appear to induce stomatal closure in darkness by increasing the internal CO2 concentration in the leaf, since this concentration should already be very high in darkness. A considerable and rapid decrease of CO2 assimilation and increase of CO2 evolution were demonstrated in mutant as well as in normal plants transferred from light to darkness. [ABSTRACT FROM AUTHOR]

A growth inhibiting substance has been extracted from mature tissues of Eucalyptus obliqua in which apical dominance occurs, but is absent in juvenile tissues of very young seedlings which show weak apical dominance. Sprouting from lignotubers in decapitated E. obliqua seedlings is correlated with a reduction in the level of inhibitory properties. Reapplied inhibitory substance, but not abscisic acid, reduced sprouting. The inhibitory substance has been partially purified and some of its properties tested, suggesting that it is not abscisic acid. [ABSTRACT FROM AUTHOR]

Distichlis spicata, a salt marsh grass, sets dormant seeds which exhibit a low-temperature, after-ripening requirement. In addition to stratification, localized scarification and nitrate are effective agents in breaking dormancy and promoting seed germination. The pericarp and/or testa are impermeable to organic plant-growth regulators, but not to water or inorganic salts. Gibberellic acid and kinetin are ineffective in breaking dormancy and do not affect germination. Abscisic acid, however, effectively inhibits stratified and scarified seeds. Dormancy and germination appear to be hormonally controlled. It is suggested that the endogenous inhibitor constitutes a block to nitrate reductase activity in the endosperm. Presumably the inhibitor blocks specific DNA transcription sites in the aleurone cells, but can be overcome by after-ripening (inhibitor decay), abrasion (inhibitor leaching) or nitrate induction. [ABSTRACT FROM AUTHOR]

A rapid bioassay for cytokinins is described. This is based on the ability of these compounds to promote markedly the expansion of radish cotyledons excised soon after seed germination. The response, which is due largely to a promotion of cell enlargement, is inhibited by abscisic acid. Gibberellins, certain amino acids and calcium salts, naturally occurring substances without cytokinin activity, induce small growth increments in the assay. Cytokinin structure-activity relation-ships observed for the assay are very similar to those which apply in the tobacco-pitch tissue culture assay. [ABSTRACT FROM AUTHOR]

Lactuca sativa L., lettuce (Arctic King) fruit germination is inhibited in the light at temperatures above 27°C(±1.5°). This value, which is precise and repeatable is referred to as the upper temperature cut‐off point, and is characteristic for a particular species. It was found, that this cut‐off point is shifted upwards by applying kinetin solutions (0.1–1 mg/1) or downwards by applying (±)‐abscisic acid solutions (over 1 mg/1), the amount of shift being proportional to the level of active compound. In the presence of both compounds a balance was achieved. Effects of stimulators and inhibitors can most explicitly be described by reference to the direction and magnitude of the shift in the upper temperature cut‐off point, which results from their application. [ABSTRACT FROM AUTHOR]

A procedure for extracting and identifying plant hormones, particularly abscisic acid (ABA) and the gibberellins (GA) was developed through modification of methods described in the literature. The procedure is particularly useful for studying more than one hormone simultaneously in a given sample, and when the supply of plant material is limited The procedure was used to isolate ABA and GA-like substances from olive tissue (i.e., leaves, buds and inflorescences). Gibberellin-like substances were identified by their action on α-amylase release from embryoless barley half-seeds. Characterization of an acidic inhibitor extracted from olive inflorescences by thin-layer chromatography, fluorescence under ultraviolet light, gas chromatography, and physiological effects on wheat coleoptile sections indicate that this inhibitor, or at least a component of it, is very similar if not identical with at least one isomeric form of synthetic abscisic acid.

Experiments were carried out with viable and nonviable rice seeds to detect the nature of germination inhibitors. An abscisic acid like factor is present in nonviable seeds but absent in viable ones. The main source of the factor is the embryo although measurable amounts are also obtained from the husk; it is not found in the endosperm however. Interaction with GA3 and IAA suggests that both the rice seed inhibitor and abscisic acid are antagonistic to GA3 and partially reversed the IAA induced growth. The similarity of the UV absorption spectra of the inhibitor and abscisic acid also proves its presence in nonviable seeds. The inhibitor suppresses the α-amylase activity both in intact and excised seeds in the same way as abscisic acid but the suppression is partially overcome with higher concentrations of GA3. [ABSTRACT FROM AUTHOR]

The role of various growth-regulating substances in tuberization in Solanum andigena was studied (1) by application of exogenous growth regulators, and (2) by studying variation in the levels of endogenous hormones under tuber-inducing and non-inducing conditions. In short-day induced cuttings tuberization was inhibited by gibberellic acid; indole acetic acid and kinetin (6-furfuryl amino purine) caused slight stimulation of tuber growth at low concentrations, but inhibited it at higher concentrations. Application of (2-chloroethyl) trimethyl-ammonium chloride (CCC) promoted tuberization in plants growing under non-inducing long-day conditions and in buds produced on isolated plugs of tuber tissue. The tuber-inducing effects of CCC were not reversed by simultaneous application of GA[SUB3]. Levels of endogenous gibberellins decreased markedly under short-day conditions, but there was no difference in the levels of endogenous abscisic acid under long and short days. The reduced levels of gibberellins were maintained for at least 2 weeks when induced plants were transferred from short-day to long-day conditions. Application of CCC under conditions which promoted tuberization caused a reduction in gibberellin levels. The role of growth hormones in the regulation of tuberization is discussed. [ABSTRACT FROM AUTHOR]

Exudation from the xylem of excised maize roots was studied in roots bathed in solutions containing kinetin or abscisic acid (ABA). Kinetin reduced the water permeability of the roots whilst ABA increased it. The action of both hormones was reversible and both were effective at concentrations of 10-6M and below. The possible in vivo role of these two hormones is discussed. [ABSTRACT FROM AUTHOR]

The effect of abscisic acid (AbA) on the growth of lateral and apical buds was studied in seedlings of Pisum sativum and some other species. The hormone was applied in three different ways: 1) directly to the lateral bud on the second node of decapitated pea seedlings as 5 μI droplets in an ethanolic solution; 2) to the cut surface of decapitated seedlings: 3) to the apical bud of intact plants. AbA directly applied in amounts of 5 to 0.1 μg to the lateral bud of the second node of decapitated seedlings had a strong inhibitory effect on the bud. Application to the cut surface of seedlings decapitated about 5 mm above the second node resulted in slight inhibition of the lateral bud on the second node and in growth promotion of the bud on the first node. When AbA at 10 to 0.1 μg was applied to the apical bud of intact seedlings, the growth of this bud was inhibited but the lateral buds grew out. It is concluded that the release of the lateral buds from apícal dominance is the result of the inhibitory effect of AbA on growth of the apical bud and of low transport of AbA. This conclusion is supported by application of GA3 and IAA, individually and each combined with AbA. [ABSTRACT FROM AUTHOR]

The occurrence of gibberellins and abscisic acid (ABA) in extracts of roots of Vicia faba was demonstrated by gas‐liquid chromatography (GLC) of the methylated eluates from the relevant zones of thin‐layer chromatograms (TLC) of purified extracts. Quantitative determination of the hormone contents in extracts from upper and lower halves of roots which had been kept in the horizontal position for 30 min indicated a redistribution of the hormones during the geotropic stimulation. Gibberellins whose methyl esters appeared at the retention time of methylated gibberellic acid (GA3), used as a standard, occurred in higher concentration in the upper than in the lower halves (ratio 2.08:1), whereas the concentration of ABA was highest in the lower halves (ratio 3.08:1). The ratio of the hormones in right and left halves of vertical roots was close to 1:1. Indoleacetic acid (IAA) and ABA were found to retard the elongation of roots of Vicia faba and Lepidium during the first 24 h. Additional experiments with Lepidium showed that this retardation occurs within the first hour after application. Low concentrations of GA3, when applied to germinating seeds just after the radicles had broken the seed coat, stimulated root elongation in Vicia faba within 24 h and in Lepidium within 36 h. When applied to Lepidium seedlings with 20 mm long roots, GA3 showed a stimulatory trend within the first 2 h, and distinct stimulation in the subsequent hours, particularly at the lowest concentrations, 0.01 and 0.001 mg/l. These results suggest the possibility of a participation of ABA and gibberellins (in addition to IAA) in the development of the positive geotropic curvature. [ABSTRACT FROM AUTHOR]

The mechanism of ABA‐induced callus formation was studied in sterile bud cultures of Citrus [Citrus sinensis (L.) Osbeck] on defined media. ABA was found to promote callus formation in the abscission zone between the petiole and the branch while inhibiting bud growth. The promoting effect of ABA was dependent on the physiological state of the shoot from which buds were excised, and on the size of the explant. Callus formation was highest in autumn and summer (i.e. younger) buds, and lowest in older buds excised from previous summer flush. GA was only slightly active in promoting callus formation when applied separately, but showed a highly synergistic effect when applied with ABA: maximal callus formation was attained at a combination of 10−5M ABA and 10−6 MGA in the medium. Subcultures of ABA‐induced callus revealed that ABA inhibited the growth of isolated subcultured callus, while IAA and kinetin, and especially GA, promoted its rapid proliferation. A general decrease in protein synthesis was found in the abscission zone during the first 5 days of induction, while total protein content changed only slightly. The results suggest that ABA‐induced callus formation in Citrus bud explants is a multiphasic phenomenon involving, at least, two stages: (1) activation of certain cells in the abscission zone by ABA, resulting in the formation of callus layers, and (2) subsequent proliferation of the callus tissue, which is dependent on the hormonal balance in the explant. This growth‐promoting effect of ABA seems to be a general phenomenon in explants exposing a cut‐surface. [ABSTRACT FROM AUTHOR]

The specific activity of isocitrate lyase rapidly increased in the megagametophytic tissue of cold-stratified seeds of ponderosa pine (Pinus ponderosa Laws) prior to and after germination. When the embryo was removed at germination, isocitrate lyase activity continued to develop. However, in the total absence of the embryo, only a small increase in the specific activity of the enzyme was observed. The development of the enzyme was inhibited by cycloheximide, actinomycin D and abscisic acid. The embryo produced an unidentified factor which enhanced the development of isocitrate lyase activity in the megagametophytic tissue. This embryo factor could not be replaced by the hormones indoleacetic acid (IAA), gibberellic acid (GA3) or benzylaminopurine (BA). Indoleacetic acid had little effect upon enzyme development. Gibberellic acid and benzylaminopurine inhibited isocitrate lyase development in the megagametophytic tissue of the seed. [ABSTRACT FROM AUTHOR]

The effects of fusicoccin on the germination of dormant, light-requiring or abscisic acid-inhibited seeds has been investigated. (1) Fusicoccin (10-6 M)induces germination in dormant wheat seeds (Triticum durum cv. Cappelli; 1972 crop) and stimulates it in seeds already relieved from dormancy (1971 crop), with an effect similar to that of gibberellic acid. (2) Fusicoccin (1.5 × 10-6 M) is more active than the two phytohormones gibberellic acid and benzyladenine and than white light in stimulating light-requiring lettuce seeds (Lactuca sativa cv. Grand Rapids) to germinate. Germination of radish seeds (Raphanus sativus) is also accelerated by fusicoccin, while benzyladenine and gibberellic acid are less active in this material. (3) Fusicoccin (1.5 × 10-5 M) removes almost completely the inhibitory effect of abscisic acid on germination of radish and lettuce seeds, whereas benzyladenine (10-4 M) and gibberellic acid (3 × 10-4 M) remove the inhibition only partially. The possible relationship between these results and previous information on growth by cell enlargement is discussed in terms of the mechanism of action of fusicoccin as compared with natural hormones. [ABSTRACT FROM AUTHOR]

The action of abscisic acid on the kinetics of auxin transport through Zea mays L. (cv. Goudster) coleoptiles has been investigated. Abscisic acid applied simultaneously with indoleacetic acid-2-14C in the donor block reduced the transport intensity without materially affecting the basipetal velocity or the uptake. No effect on acropetal transport was observed. The data have been used to discuss the similarities in effects of abscisic acid and visible radiation and a hypothesis is proposed to explain the phenomena of phototropism. [ABSTRACT FROM AUTHOR]

Abscisic acid inhibited the rate of 14CO2 fixation in leaves of Pennisetum typhoides (Burm. f.) Stapf & Hubbard seedlings, but increased the activities of phosphoenol-pyruvate-carboxylase and malic enzyme. The leaves of the seedlings grown in the presence of abscisic acid incorporated, in comparison to the control, more radioactivity in the fraction of organic acids, but less radioactivity was recorded in the amino acid fraction. On the other hand, gibberellic acid which also inhibits photosynthetic 14CO2 assimilation and decreases the activities of photosynthetic enzymes, favours greater incorporation in alanine, and reduces that in malate. It is deduced that bio-regulants can greatly influence the flow of 14C into individual photosynthetic products. As in growth, abscisic and gibberellic acids in combination tended to antagonize each other in their effects on enzyme activity as well as in incorporation of 14CO2 into photosynthetic products. [ABSTRACT FROM AUTHOR]

Heat treatments of two minutes at 46 to 47°C to root systems of Nicotiana rustica and Phaseolus vulgaris affected roots and shoots. Xylem exudate of Phaseolus was collected, and it was found that heat treatment reduced cytokinin levels and increased abscisic acid levels in the exudate. Shoot and root growth of both species was reduced.. Root membrane integrity of Nicotiana was measured and was found to be impaired. It is suggested that the changes in hormone activity due to heat treatment regulate the reduction in shoot growth. Cell wall metabolism and glucosyl transferases making β-glucans were investigated in Phaseolus leaves. Incorporation of 14C from 14CO2 into wall constituents was slightly inhibited but neither photosynthesis nor extracted β-glucan synthetases were affected during the first 12 hours after treatment. [ABSTRACT FROM AUTHOR]

Water-soluble compounds isolated from Laminaria digitata and Ascophyllum nodosum caused marked inhibition of lettuce hypocotyl growth. GLC analysis of these substances showed, in one case, properties similar to ABA (abscisic acid) but definite information on this must be deferred until the chemical nature of the seaweed compound is verified. The possible role of these compounds in seaweed growth and their possible significance as ectocrines in the sea, are discussed. [ABSTRACT FROM AUTHOR]

Applications of ABA to Cymbidium flowers induce some, but not all, post-pollination symptoms. Anthocyanin levels in sepals, petals, columns and labella are raised; flowers wilt; dorsal sepals become hooded; calli develop colouration while losing turgidity; columns do not swell, lose very little curvature; and stigmas do not close. Combinations of ABA and NAA induce all post-pollination phenomena, but lower anthocyanin content than treatments with ABA only. ABA plus GA[sub3] have effects which are similar to those of ABA alone, except that anthocyanin levels are reduced. The same is essentially true of ABA-kinetin mixtures but intensities of the effects are different and with some concentration ratios, stigmatic closure also occurs. The effects of ABA and its interactions with GA[sub3], kinetin or NAA arc explained in terms of the roles these hormones may play in synthesis of nucleic acids and enzymes. [ABSTRACT FROM AUTHOR]

Endogenous levels of abscisic acid-like inhibitors doubled within 15 minutes of leaf excision in Vitis vinifera under laboratory conditions. At that stage water potential (ψ) had fallen to -15 bars and stomatal closure was occurring. After prolonged stress (6 days and final ψ -13 bars) inhibitor levels in intact vine leaves increased by a factor of 44 but showed a rapid decline following rewatering. Photosynthetic activity was not immediately restored, and its gradual recovery was not directly related to inhibitor level, [ABSTRACT FROM AUTHOR]

The formation of adventitious buds and roots in leaf discs of Streptocarpus × hybridus 'Constant Nymph' were both stimulated by relatively low temperatures (12 and 18°C) applied to isolated discs or to the growing plants before leaf harvest. Auxins also promoted both bud and root formation, the optimum concentration for rooting always being one to two orders of magnitude higher than the optimum for budding. cytokinins had only a small stimulatory effect on bud formation. At higher concentrations it was inhibitory and even counteracted the stimulatory effect of auxin on bud formation. As usual, root formation was inhibited by cytokinin. GA3 inhibited both bud and root formation but the inhibition was reversible by auxin. In presence of optimum auxin I levels abscisic acid enhanced bud formation. It had little effect on root formation except for an inhibition at high concentrations. The effects of exogenous auxin and cytokinin suggest that Streptocarpus leaves have a high and non-limiting level of endogenous cytokinin with auxin as the limiting factor for both root and bud formation. This would also explain the exceptionally high regeneration ability of this plant. [ABSTRACT FROM AUTHOR]

A single surface application of abscisic acid or its methyl and phenyl esters suppressed stomatal opening on leaves of Xanthium strumarium. The effect was restricted to the treated parts of the leaf blades, there being no detectable translocation to untreated parts. There were no increases in CO2 compensation to which stomatal closure could be attributed. Abscisic acid and its esters acted successfully as antitranspirants when applied once to leaf surfaces of young barley plants. Over a 9-day period there was a reduction of about 50 % in the amount of water transpired without any detect- able reduction in the rate of dry weight increase. The treatments reduced transpiration relatively more than dry matter accumulation, and hence there was an increase in the water use efficiency. The effect of the treatments became progressively less over 9 days, but even at the end of the experiment (day 9) both the esters reduced transpiration by 20-25 %. The esters were slightly more effective than abscisic acid itself. On the basis of the data presented here, field trials of the antitranspirant properties of these compounds are recommended. [ABSTRACT FROM AUTHOR]

Several experiments have been performed to analyse the ABA effects on the basipetal transport of IAA-2-14C, using sections of epicotyls prepared from etiolated Lens seedlings. The sections were incubated in an ABA solution or ABA was applied in the donor blocks containing IAA. For each type of assay, the uptake (analyses of the donor blocks) and the movement of IAA-C14 (analyses of the receiver blocks) were inhibited by ABA. The distribution of continuous decrease of the radioactivity, along the sections' axis, showed a 14C level from the apical towards the basal segments. ABA caused a decrease in the 14C concentration for the total sections, but a relative increase for the basal segment. When ABA was applied simultaneously with IAA in the donor blocks, the transport velocity of IAA, through the sections, was not changed significantly, while an ABA pretreatment caused a significant decrease. [ABSTRACT FROM AUTHOR]

By means of experimentation with the barley endosperm system and with peroxidase isoenzyme production during culture of tobacco pith the mode of action of abscisic acid (ABA) was investigated. Gibberellic acid (GA3) promoted reducing sugar production was significantly inhibited by ABA and bovine pancreas ribonuclease (RNase), while the specific RNA polymerase inhibitor rifamycin was without effect. In tobacco pith culture, ABA promoted appearance of induced isoenzymes, the effect being completely checked by rifamycin. Furthermore ABA significantly inhibited, and GA3 promoted production of RNA in treated tobacco plants. It is suggested that the mode of ABA action in these systems may be an inductive one on the degradative enzyme, RNase, and not necessarily a negative one on the promotive RNA polymerase. This conclusion implies effect on some preexisting RNA, the breakdown of which is mediated by ABA‐activated RNase. [ABSTRACT FROM AUTHOR]

Lycopene biosynthesis of parenchyma chromoplasts was studied in detached tomato fruits, Lycopersicum esculentum Mill. cv. Waltham forcing, and found to be phytochrome mediated. A few minutes of red light during the day enhanced lycopene formation. Far-red irradiation did not enhance lycopene biosynthesis. Far-red following red nullified the promotive effect of red light. Lycopene content increased two-fold in the presence of abscisic acid. Ripening of tomatoes was inhibited when gibberellin, kinetin and ascorbic acid were applied to green tomatoes. Gibberellin (A3) was more inhibitory to lycopene synthesis than kinetin. [ABSTRACT FROM AUTHOR]

The regulative systems of auxins, gibberellin-like substances and their inhibitors in citrus fruit were studied. Masking caused by a high content of inhibitors was eliminated by using a refined method of solvent partition. Considerable amounts of auxins and gibberellin-like substances were detected in all stages of fruit development. The auxin system of the citrus fruit is highly complex and consists of various elements which undergo dynamic changes throughout the growth period. The identity of the auxins was studied using IAA-2-14C, and 88% of the radioactivity specifically migrated into the etheric pH 6.0 fraction. Although the prominent zones of promotion do not coincide with IAA, it can be concluded that the auxin promoters are probably not the "citrus auxin". Abscisic acid-like inhibitors were found to accumulate in the external layers of the fruit, increasing in content as time advances. [ABSTRACT FROM AUTHOR]

The effects of abscisic acid, salicylic acid and trans-cinnamic acid were tested on the light-induced phosphorylating reactions and oxygen evolution of the unicellular green alga Scenedesmus. It was found that abscisic acid and cinnamic acid had practically no influences on the total inorganic phosphate uptake, while salicylic acid in the concentration range of 10-6 to 10-3 M gave a small decrease in the total inorganic phosphate uptake. The ATP level in the cells is in most cases increased when these three acids are given to the algae. The oxygen output is not significantly changed by abscisic acid or salicylic acid. Trans-cinnamic acid inhibits the oxygen evolution at concentrations of 10-4-10-3 M. None of the substances investigated caused such effects on photophosphorylation and oxygen evolution in Scenedesmus as those caused by the inhibitor β-complex from potatoes according to earlier reports. It is suggested that those effects are due to other components in the inhibitor β-complex. [ABSTRACT FROM AUTHOR]

The effect of cytokinins and gibberellic acid on the inhibition of growth and α-amylase synthesis by germination inhibitors was investigated in intact and embryoless seed halves. The cytokinins, kinetin and benzyladenine, effectively reversed the inhibition of coleoptile growth and α-amylase synthesis by abscisic acid and coumarin in barley seed. An antagonism between cytokinins and germination inhibitors was also shown in root growth. Abscisic acid inhibited coleoptile growth to a greater extent than the root growth while the opposite held true in the case of coumarin. The apparent increase in coleoptile growth and α-amylase synthesis by gibberellic acid plus abscisic acid (or coumarin) over abscisic acid (or coumarin) appears to be a result of the overall stimulation of growth and metabolism by exogenous gibberellic acid and probably does not involve an interaction of gibberellic acid with the inhibitors. Gibberellic acid reversed root inhibition to some extent. Abscisic acid inhibition of gibberellic acid induced α-amylase synthesis in the embryoless endosperm was not reversed by excess gibberellic acid or kinetin. Cytokinin reversal of inhibition of growth and enzyme synthesis probably depends on some factor(s) in the embryo. Cytokinin reversal of inhibitor action leading to enzyme synthesis and growth may be at the level of genome or at the site of protein assembly. [ABSTRACT FROM AUTHOR]

The effect of cytokinin, kinetin, on abscisic acid (dormin) inhibition of α-amylase synthesis and growth in intact barley seed was investigated. Abscisic acid at 5 × 10-5 M nearly completely inhibited growth response and α-amylase synthesis in barley seed. Kinetin reversed to a large extent abscisic acid inhibition of α-amylase synthesis and coleoptile growth. The response curves of α-amylase synthesis and coleoptile growth in presence of a fixed amount of abscisic acid (6 × 10-6 M) and increasing concentrations of kinetin (from 5 × 10-7 M to 5 × 10-5 M) showed remarkable similarity. Kinetin and abscisic acid caused synergistic inhibition of root growth. Gibberellic acid was far less effective than kinetin in reversing abscisic acid inhibition of α-amylase synthesis and coleoptile growth. A combination of kinetin and gibberellic acid caused nearly complete reversal of abscisic acid inhibition of α-amylase synthesis but not the abscisic acid inhibition of growth. The results suggest that factors controlling α-amylase synthesis may not have a dominant role in all growth responses of the seed. Kinetin possibly acts by removing the abscisic acid inhibition of enzyme specific sites thereby allowing gibberellic acid to function to produce α-amylase. [ABSTRACT FROM AUTHOR]

Observations have been made on the effect of synthetic, (±)-abscisin II (dormin), alone and in combination with gibberellin, kinetin and indoleacetic acid, on seed germination and seedling growth of two strains of lettuce, cv. Attraktion and cv. Hohlblättriger Butter. (±)-Abscisin II inhibited seed germination and seedling growth in both strains. The inhibitory effect of abscisin II on seed germination as well as seedling growth was completely overcome by kinetin in both dark and light. Gibberellic acid, on the other hand, proved ineffective in exerting its influence on seed germination in presence of abscisin II but affected subsequent seedling growth as usual. Indoleacetic acid was found to be least potent in reversing abscisin II caused inhibition of seed germination and seedling growth. It is concluded, that like its effect on certain other naturally occurring inhibitors of seed germination, kinetin can effectively undo the inhibitory effects of abscisin II in these growth processes. [ABSTRACT FROM AUTHOR]

The present investigation deals with the influence of auxin and kinetin on cultures of potato tuber tissue, and the effect of the size of the explants on the organ formation. Exogenous application of auxin is indispensable for initiating callus formation of the tissue, but kinetin is not necessarily required. Kinetin serves to maintain the callus development, indicating that the stimulation of callus growth due to exogenous auxin would presumably be mediated by the addition of kinetin to the medium. A relatively low concentration of auxin in the medium is required for root formation on the culture. In this case, IAA is markedly superior to any other auxin in root forming activity. NAA is somewhat less effective than IAA, and 2,4-D shows no stimulation on root formation. The growth and organ formation of potato tissue are remarkably affected by the variation in sizes of the explants. Spontaneous formation of a sprout was observed on the large explant in the medium without auxin. Small explants form only callus or roots in the presence of auxin and kinetin irrespective of combination or concentration. It seems likely that a sufficient amount of stimulus for initiation of bud formation may be contained in the large sized explant itself. [ABSTRACT FROM AUTHOR]

(1) The further the sections are from the apex, the less is the endogenous growth and the response to GA and sucrose, and the greater is the relative response to IAA as compared with GA. (2) Longer sections are less sensitive to sucrose, and they show greater elongation than the corresponding short sections at a given distance from the apex. Longer sections may contain tissues heterogeneous in their response to IAA and GA. (3) Our results underline the necessity of accurately specifying the type of sections employed in pea section growth tests. Small sections taken very close to the apex may prove to he a useful bioassay material for the gibberellins. [ABSTRACT FROM AUTHOR]

Eleven growth substances were tested for their bud producing capacity in Funaria hygrometrica. IAA and gibberellic acid showed no response, neither did inositol, abscisic acid and adenine. The cytokinins: benzylaminopurine, kinetin and mercaptopurine showed a quantitative relationship while methylaminopurine did not. When different amounts of abscisic acid were added together with 10 μg kinetin (which gave maximal production of buds), there existed a linear relationship between reduction in buds and abscisic acid added. Results are obtained in two weeks and it is therefore a fairly quick method for assaying certain cytokinin and also abscisic acid.

Different amounts of abscisic acid, 2.7 × 10-9 - 5 × 10-8 moles, were chromatographed in isopropanol : ammonia : water (100 : 14 : 6), firstly alone and secondly together with 5 × 10-8 moles kinetin. The same amount of kinetin was also chromatographed alone. The chromatograms were tested biologically with the Avena straight-growth test. Whereas a large part of the chromatograms of kinetin gives growth stimulation, the Rf region 0.4-0.6 of abscisic acid chromatograms is strongly growth-inhibiting. The inhibition within this Rf region does not become less if abscisic acid and kinetin are chromatographed together. [ABSTRACT FROM AUTHOR]