Metabolism of abscisic acid and the occurrence of epi-dihydrophaseic acid in Phaseolus vulgaris

When (±)-abscisic acid-[2-¹⁴C] or (±)-abscisic acid-[4′-¹⁸O] was fed to bean (Phaseolus vulgaris) shoots, phaseic acid (PA) and dihydrophaseic acid (DPA) were the major metabolites, while epi-dihydrophaseic acid (epi-DPA) appeared as a minor metabolite. In the acidic fraction the amount of epi-DPA ranged from 18 to 42% of the DPA content, in the conjugated form from 50 to 200%. The content of endogenous epi-DPA amounted to only 1–2% of that of the DPA. These data indicate that the applied abscisic acid is not metabolised in a manner identical with that of the endogenous material. DPA and epi-DPA were shown to be formed separately from PA and could not be inter-converted either by the extraction conditions employed or when fed to bean shoots during short term experiments.     

Dormancy termination of western white pine (<Emphasis Type="Italic">Pinus monticola</Emphasis> Dougl. Ex D. Don) seeds is associated with changes in abscisic acid metabolism

Western white pine (Pinus monticola) seeds exhibit deep dormancy at maturity and seed populations require several months of moist chilling to reach their uppermost germination capacities. Abscisic acid (ABA) and its metabolites, phaseic acid (PA), dihydrophaseic acid (DPA), 7-hydroxy ABA (7OH ABA) and ABA-glucose ester (ABA-GE), were quantified in western white pine seeds during dormancy breakage (moist chilling) and germination using an HPLC–tandem mass spectrometry method with multiple reaction monitoring and internal standards incorporating deuterium-labeled analogs. In the seed coat, ABA and metabolite levels were high in dry seeds, but declined precipitously during the pre-moist-chilling water soak to relatively low levels thereafter. In the embryo and megagametophyte, ABA levels decreased significantly during moist chilling, coincident with an increase in the germination capacity of seeds. ABA catabolism occurred via several routes, depending on the stage and the seed tissue. Moist chilling of seeds led to increases in PA and DPA levels in both the embryo and megagametophyte. Within the embryo, 7OH ABA and ABA-GE also accumulated during moist chilling; however, 7OH ABA peaked early in germination. Changes in ABA flux, i.e. shifts in the ratio between biosynthesis and catabolism, occurred at three distinct stages during the transition from dormant seed to seedling. During moist chilling, the relative rate of ABA catabolism exceeded ABA biosynthesis. This trend became even more pronounced during germination, and germination was also accompanied by a decrease in the ABA catabolites DPA and PA, presumably as a result of their further metabolism and/or leaching/transport. The transition from germination to post-germinative growth was accompanied by a shift toward ABA biosynthesis. Dormant imbibed seeds, kept in warm moist conditions for 30 days (after an initial 13 days of soaking), maintained high ABA levels, while the amounts of PA, 7OH ABA, and DPA decreased or remained at steady-state levels. Thus, in the absence of conditions required to break dormancy there were no net changes in ABA biosynthesis and catabolism.Abbreviations ABA abscisic acid - ABA-GE abscisic acid glucose ester - DPA dihydrophaseic acid - 7OH ABA 7-hydroxy abscisic acid - 8OH ABA 8-hydroxy abscisic acid - MRM multiple reaction monitoring - PA phaseic acid     

Changes in the levels of abscisic acid and its metabolites resulting from chilling of tomato fruits

The 6,6,6-[²H]-analogues of abscisic acid (ABA), phaseic (PA) and dihydrophaseic (DPA) acids were used in GC-MS-SIM determination of free and total alkali hydrolyzable ABA, PA and DPA in the pericarp of tomato (Lycopersicon esculentum L. cv. Pik Red) fruit. Determinations were made on breaker-stage fruit stored 1, 2, 3 or 4 weeks at 2.5°C or at 10°C, and after subsequent ripening for 1 week in darkness at 20°C. Two-fold increases in levels of ABA occurred after storage at low temperatures with a slightly but significantly greater increase in ABA level occurring with 2.5°C storage. These increases in ABA levels were not associated with the appearance of damage symptoms that occurred with storage at the chilling temperature (2.5°C). Differences in ABA metabolism were found resulting from storage at the two temperatures, 2.5 or 10°C. Significantly greater DPA levels were found after 10°C storage than after 2.5°C storage (2 weeks). Levels of ABA ester-conjugates increased with 20°C ripening only after 10°C storage while free ABA levels decreased after both storage temperature conditions. Levels of DPA conjugates also increased only after 20°C ripening following 10°C storage. A longer period of storage resulted in decreases of free DPA levels after 10°C storage but increased DPA levels were found after 2.5°C storage.Abbreviations ABA abscisic acid - PA phaseic acid - DPA dihydrophaseic acid - GC-MS-SIM gas chromatography-mass spectrometry-selected ion monitoring - HPLC high pressure liquid chromatography - fw. fresh weight author for correspondence     

Relationship between ABA and chilling injury in mangosteen fruit treated with spermine

Theeffects of spermine on abscisic acid (ABA), hardening, and browning in storedmangosteen fruit were investigated. The hardening and browning, which areassociated with chilling injury (CI), were observed in only the skin of fruitstored at 7 °C. However, the hardening of skin was notaccompanied by moisture loss. The spermine treatment decreased the browning andhardening of the skin and extended storage time. Carbon dioxide(CO₂)production from stored fruit gradually increased with d in storage(DIS). The increase of CO₂ may be associated with the moisture lossbecause these levels coincided. ABA concentrations in the skin were highest infruit stored at 7 °C, followed by spermine treatment at 7°C, and the lowest at 13 °C. That is, thespermine treatment inhibited the increase of ABA in the skin of stored fruit.ABA concentrations in the skin may be associated with the degree of CI becausetheir fluctuations coincided. ABA metabolism in fruit stored at 7°C or 13 °C was also examined. The PA-DPApathway may not be the primary pathway of ABA metabolism because theconcentrations of PA and DPA were very low compared with those of ABA. ABAconcentrations in the aril were not significantly different between 7°C and 13 °C. This may be related to the lackof CI observed in the aril. ABA metabolism was different at each temperature.The decrease of ABA and the increase of DPA correlated at 13°C, however this correlation was not observed at 7°C. ABA metabolism may be influenced by temperature.     

Regulation of carotenoid and ABA accumulation during the development and germination of Nicotiana plumbaginifolia seeds

Abscisic acid (ABA) is derived from epoxycarotenoid cleavage and regulates seed development and maturation. A detailed carotenoid analysis was undertaken to study the contribution of epoxycarotenoid synthesis to the regulation of ABA accumulation in Nicotiana plumbaginifolia developing seeds. Maximal accumulation of xanthophylls occurred at mid-development in wild type seeds, when total ABA levels also peaked. In contrast, in ABA-deficient mutants xanthophyll synthesis was delayed, in agreement with the retardation in seed maturation. Seed dormancy was restored in mutants impaired in the conversion of zeaxanthin into violaxanthin by zeaxanthin epoxidase (ZEP), by the introduction of the Arabidopsis AtZEP gene under the control of promoters inducing expression during later stages of seed development compared to wild type NpZEP, and in dry and imbibed seeds. Alterations in the timing and level of ZEP expression did not highly affect the temporal regulation of ABA accumulation in transgenic seeds, despite notable perturbations in xanthophyll accumulation. Therefore, major regulatory control of ABA accumulation might occur downstream of epoxycarotenoid synthesis.     

Development and regulation of three glyoxysomal enzymes during cotton seed maturation and growth

The temporal, nonconcerted development of activities of malate synthase (MS), isocitrate lyase (ICL), and catalase (Cat) was explored in more detail in maturing and germinated cotton (Gossypium hirsutum L.) seeds. RNA was extracted at six intervals beginning at 17 days post anthesis (DPA) through 72 hours post imbibition (HPI). In vitro translations revealed that mRNAs for each enzyme were translatable at all intervals. Enzyme activities and immunoselected proteins also were found at all intervals. Similar specific activities throughout maturation indicated that embryo cells were not accumulating inactive protein. The steady-state level of mRNAs encoding each enzyme exhibited different patterns of change during seed maturation, and each peaked at least 24 h before peak enzyme activities in germinated seeds. All three enzymes occur together as early as 17 DPA in a coordinate manner; however, the subsequent, nonconcerted increases in protein, activity, and mRNA for each enzyme indicate that developmental expression in cotton seed embryos is regulated in a noncoordinate fashion by as yet unidentified specific control mechanism(s).Abbreviations ABA abscisic acid - bp base pairs - DPA days post anthesis - HPI hours post imbibition - kb kilobase (pairs) - M _r relative molecular weight - S Svedberg unit (10^-13s)     

Abscisic acid levels and metabolism in the leaf epidermal tissue of Tulipa gesneriana L. and Commelina communis L.

We have shown the presence of abscisic acid (ABA) in abaxial epidermal strips taken from Tulipa gesneriana and Commelina communis and that the ABA level rises in the epidermis when leaves are water stressed. ABA levels had risen 50% in the abaxial epidermis of C. communis 30 min after the leaves lost 10% of their fresh weight. Epidermis from both T. gesneriana and C. communis metabolize [¹⁴C]ABA to several products probably including phaseic acid (PA) and dihydrophaseic acid (DPA).Abbreviations ABA abscisic acid - RIA radioimmunoassay - PA phaseic acid - DPA dihydrophaseic acid - TLC thin-layer chromatography - GC gas chromatography     

Identification by combined gas chromatography-mass spectrometry of phaseic acid and dihydrophaseic acid and characterization of further abscisic acid metabolites in pea seedlings

Seven day old seedlings of Pisum sativum L., cv. Kleine Rheinländerin, were wilted for 3 days. After partially removing the roots, they were rewatered and at the same time radioactive abscisic acid([1-¹⁴C]ABA, spec. activity 1.7·10⁸d s^-1mmol^-1) was applied for 1 h via the xylem of the roots. After 24 h, 4 days, and 12 days the seedlings were extracted and the metabolites of ABA were analyzed by means of thin-layer and gas chromatography in combination with mass spectrometry, autoradiography, and scintillation counting. Phaseic acid (PA) and dihydrophaseic acid (DPA) were identified as metabolites of ABA. The presence of another ABA-metabolite was also demonstrated. From its mass spectrum it has been postulated that this metabolite is 4-desoxy-ABA. In addition to these substances, several other metabolites, which are more polar than ABA and its known degradation products, were present in the seedlings. The quantity and number of these unknown metabolites increased with time.Abbreviations ABA abscisic acid - PA phaseic acid - DPA dihydrophaseic acid - TLC thin-layer chromatography - GC gas chromatography - PPO 2,5-diphenyloxazole - POPOP 2,2-p-phenylen bis(5-phenyloxazole)     

Disrupting Abscisic Acid Homeostasis in Western White Pine (<Emphasis Type="Italic">Pinus monticola</Emphasis> Dougl. Ex D. Don) Seeds Induces Dormancy Termination and Changes in Abscisic Acid Catabolites

To investigate the role of abscisic acid (ABA) biosynthesis and catabolism in dormant imbibed seeds of western white pine (Pinus monticola), ABA and selected catabolites were measured during a combined treatment of the ABA biosynthesis inhibitor fluridone, and gibberellic acid (GA). Fluridone in combination with GA effectively disrupted ABA homeostasis and replaced the approximately 90-day moist chilling period normally required to break dormancy in this species. Individually, both fluridone and GA treatments decreased ABA levels in the embryos and megagametophytes of white pine seeds compared to a water control; however, combined fluridone/GA treatment, the only treatment to terminate dormancy effectively, led to the greatest decline in ABA content. Fluridone treatments revealed that a high degree of ABA turnover/transport occurred in western white pine seeds during the initial stages of dormancy maintenance; at this time, ABA levels decreased by approximately two-thirds in both embryo and megagametophyte tissues. Gibberellic acid treatments, both alone and in combination with fluridone, suggested that GA acted transiently to disrupt ABA homeostasis by shifting the ratio between biosynthesis and catabolism to favor ABA catabolism or transport. Increases in phaseic acid (PA) and dihydrophaseic acid (DPA) were observed during fluridone/GA treatments; however, increases in ABA metabolites did not account for the reduction in ABA observed; additional catabolism and/or transport of ABA and selected metabolites in all probability accounts for this discrepancy. Finally, levels of 7′ hydroxy-ABA (7′OH-ABA) were higher in dormant-imbibed seeds, suggesting that metabolism through this pathway is increased in seeds that maintain higher levels of ABA, perhaps as a means to further regulate ABA homeostasis.     

Maternal synthesis of abscisic acid controls seed development and yield in<Emphasis Type="Italic"> Nicotiana plumbaginifolia</Emphasis>

The role of maternally derived abscisic acid (ABA) during seed development has been studied using ABA-deficient mutants of Nicotiana plumbaginifolia Viviani. ABA deficiency induced seed abortion, resulting in reduced seed yield, and delayed growth of the remaining embryos. Mutant grafting onto wild-type stocks and reciprocal crosses indicated that maternal ABA, synthesized in maternal vegetative tissues and translocated to the seed, promoted early seed development and growth. Moreover ABA deficiency delayed both seed coat pigmentation and capsule dehiscence. Mutant grafting did not restore these phenotypes, indicating that ABA synthesized in the seed coat and capsule envelope may have a positive effect on capsule and testa maturation. Together these results shed light on the positive role of maternal ABA during N. plumbaginifolia seed development.Abbreviations ABA Abscisic acid - DAP Days after pollination - g Grafted - Wt Wild-type     

Changes in abscisic acid levels in embryo axes of Norway maple and sycamore seeds during maturation and dehydration

Changes in the abscisic acid (ABA) levels in embryo axes of seeds, belonging to the orthodox (Norway maple — Acer platanoides L.) and recalcitrant (sycamore — Acer pseudoplatanus L.) categories, were investigated throughout maturation using an ELISA (enzyme-linked immunosorbent assay) test. Concentration of ABA in embryo axes substantially differed depending on species and sampling date. ABA was always higher in Norway maple except at the end of seed maturation when ABA content was similar in both species. During maturation ABA decreased in both species but the decline was more marked in Norway maple than in sycamore (11 vs. 3 fold). These species also differed in the pattern of ABA changes, which in sycamore embryo axes was very regular, while in Norway maple a sharp decrease was recorded after acquisition by the seeds of tolerance to desiccation. Dehydration of embryo axes of Norway maple caused a further significant decrease of ABA level. In contrast, in dehydrated sycamore embryo axes ABA content did not decrease, but slightly increased. The role of ABA in desiccation tolerance and dormancy of Norway maple and sycamore seeds is discussed.     

Evidence of a role for tyrosine dephosphorylation in the control of postgermination arrest of development by abscisic acid in Arabidopsis thaliana L

In the present paper evidence is presented indicating that tyrosine dephosphorylation is a key regulatory mechanism in postgermination arrest of Arabidopsis thaliana L. seed development mediated by abscisic acid (ABA). By using phenylarsine oxide (PAO), an inhibitor of tyrosine phosphatases, the sensitivity to the inhibitory effect of ABA on seed germination is enhanced. Consistent with this finding, we demonstrate that the ABA-responsive gene, RAB18, is hyperinduced in seeds imbibed in ABA plus PAO, compared with seeds imbibed only with ABA.     

Diversities in morphological characteristics and seed germination behavior in fruits ofSalsola komarovii Iljin

Two different types of dispersal units (called fruits in this study) were observed inSalsola komarovii Iljin. One is a fruit which has dark brown lignified tepals with long wings and a green seed and falls easily from the mother plant (long-winged type). Another has light brown lignified tepals with short wings and a yellow seed and attaches tightly to the mother plant (short-winged type). This difference of fruit type appeared independently from maturity of fruit. Seeds in the short-winged fruits were in dormancy for a longer period of time than those in the long-winged fruits. The germination rate was significantly higher in the seeds of long-winged fruits. The dormancy in seeds of the long-winged fruits was effectively terminated by reducing the temperature but the effect of chilling was very weak in seeds of the short-winged fruits. It was concluded from these observations that there exists a dimorphism in the fruits of, or a heterocarpy in,S. komarovii. The plants grown under water stress produced mostly short-winged fruits and those grown under well-watered conditions bore fruits of both types. Exogenously applied abscisic acid (ABA) tended to produce the short-winged fruits, suggesting that the heterocarpy was, at least partly, regulated by ABA.     

Abscisic acid and osmotic induction of synchronous somatic embryo development of sweet potato

Summary Somatic embryos of sweet potato have potential as synthetic seeds. The effects of abscisic acid (ABA) (0,0,0.1, 1.0, 10.0 and 50.0 μM) were examined to improve synchrony and proliferation of somatic embryos. Transferring embryos compared to those cultures transferred at day 0. The development of embryos in suspension culture supplemented with ABA was poor. However, when calli proliferation cultures were in gelled medium and pulsed with 0.1 μM ABA for 14 d, the number of somatic embryos increased. Proembryonic masses cultured in mannitol-containing medium (Y=−1.5 MPa) increased embryo development and synchrony of embryo development. Thus, in this work ABA and mannitol have been shown to improve both the total number and the synchrony of sweet potato somatic embryos.     

The isolation of an abscisic-acid metabolite, 4′-dihydrophaseic acid,from non-imbibed Phaseolus vulgaris seed

Summary Naturally occurring 4-dihydrophaseic acid (DPA) has been isolated from mature, non-imbibed bean seed. The concentrations of abscisic acid (ABA), phaseic acid (PA) and DPA in the seed were estimated to be 0.06, 0.11 and 5.95 mg/kg dry wt., respectively. The results suggest that DPA is a major inactivation product of ABA in this tissue. The possible pathway from ABA to DPA is discussed.Abbreviations ABA abscisic acid - DPA 4-dihydrophaseic acid - PA phaseic acid     

Roles of jasmonic acid in the development of sweet cherries as measured from fruit or disc samples

The effect of jasmonic acid (JA) on callus formation was investigated ondiscs taken from the pulp of sweet cherry fruit (Prunusavium L.). The discs were sampled at 16 days after full bloom(DAFB),22 DAFB, and 29 DAFB and cultured on B5 medium involving different combinationsof 1-naphthaleneacetic acid (NAA), N⁶-benzyl adenine (BA), and JA.Only at 16 DAFB, 1.0 M JA concentration increased callusweightgain relative to discs incubated without hormonal additives, although JAinhibited, or had no effect on callus formation, at 22 and 29 DAFB. The weightof the callus, which was subcultured, was also increased by 0.45–1.0M JA, without hormonal additives. Although the number of cellsincreased until 15 DAFB, after this time it did not change. These resultsdemonstrate that endogenous JA may be related to cell division in sweet cherryfruit. The interactions between JA and abscisic acid (ABA) were alsoinvestigated. Discs from pulp at 20 DAFB (immaturity), 32 DAFB (beforematuration), and 48 DAFB (maturation) were placed in petri dishes containing 10ml 0.4 M mannitol with JA or ABA. In addition, at 48DAFB, JA or ABA solutions had been absorbed by the fruit for 7 days via theshoot. ABA treatment did not influence endogenous JA concentrations in discs,with few exceptions. Although the ABA concentration in the fruit increased to2.2 times that of the control by ABA the 7 day treatment, endogenous JA failedto increase. Thus, ABA may not influence the JA pathway in sweet cherry fruit.Although the increase of endogenous ABA was observed in discs at earlier timesafter JA treatment, ABA concentration decreased in the fruit treated for 7 dayswith JA. This implies that the concentration of JA may influence ABA levels. JAtreatment did not influence anthocyanin accumulation, in spite of the increaseof JA in the fruit by the treatment. JA may not play a role in anthocyaninaccumulation in sweet cherry fruit.     

Dormancy of<Emphasis Type="Italic"> Arabidopsis</Emphasis> seeds and barley grains can be broken by nitric oxide

Seeds of Arabidopsis thaliana (L.) Heynh. and grains of barley (Hordeum vulgare L.) were used to characterize the affects of nitric oxide (NO) on seed dormancy. Seeds of the C24 and Col-1 ecotypes of Arabidopsis are almost completely dormant when freshly harvested, but dormancy was broken by stratification for 3 days at 4°C or by imbibition of seeds with the NO donor sodium nitroprusside (SNP). This effect of SNP on dormancy of Arabidopsis seeds was concentration dependent. SNP concentrations as low as 25 M reduced dormancy and stimulated germination, but SNP at 250 M or more impaired seedling development, including root growth, and inhibited germination. Dormancy was also reduced when Arabidopsis seeds were exposed to gasses that are generated by solutions of SNP. Nitrate and nitrite, two other oxides of nitrogen, reduced the dormancy of Arabidopsis seeds, but much higher concentrations of these were required compared to SNP. Furthermore, the kinetics of germination were slower for seeds imbibed with either nitrate or nitrite than for seeds imbibed with SNP. Although seeds imbibed with SNP had reduced dormancy, seeds imbibed with SNP and abscisic acid (ABA) remained strongly dormant. This may indicate that the effects of ABA action on germination are downstream of NO action. The NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3 oxide (cPTIO) strengthened dormancy of unstratified and briefly stratified Arabidopsis seeds. Dormancy of three cultivars of barley was also reduced by SNP. Furthermore, dormancy in barley grain was strengthened by imbibition of grain with cPTIO. The data presented here support the conclusion that NO is a potent dormancy breaking agent for seeds and grains. Experiments with the NO scavenger suggest that NO is an endogenous regulator of seed dormancy.Abbreviations ABA Abscisic acid - cPTIO 2-(4-Carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3 oxide - GA Gibberellin - SNP Sodium nitroprusside - NO_x Gaseous oxides of nitrogen     

Fatty acid synthesis in isolated leucoplasts of developing seeds of <Emphasis Type="Italic">Brassica campestris</Emphasis> L

Under in vitro conditions, the fatty acid synthesis from labelled substrates was studied in the leucoplasts isolated from developing seeds of Brassica campestris L. The rate of fatty acid synthesis with Na-(1-¹⁴C) acetate was higher at lower concentrations (up to 1 mM). However, with ¹⁴C(U)-D-glucose, the rate was higher at higher concentrations (3–4 mM) at all the three stages of seed development. ATP and NAD(P)H were absolutely required in acetate utilization. Even for glucose utilization, the exogenous supply of ATP and NAD(P)H was required. At the early stage of seed development, the maximum reduction in labelled glucose and acetate utilization for fatty acid synthesis was observed with pyruvate and glucose, respectively. However, at mid-early and mid-late stages, maximum reduction in their utilization for fatty acid synthesis was observed with glc-6-P. This suggests a shift in the utilization of substrates for fatty acid synthesis during the development of seeds probably via different translocators activated at different stages.     

Endogenous levels of polyamines and abscisic acid in pepper fruits during growth and ripening

The levels of polyamines (PA) and abscisic acid (ABA) in the pericarp of California variety pepper fruit ( Capsicum annuum L.) were analyzed during development and ripening. Putrescine level was 2.75 μmol g⁻¹ fresh weight 7 days after fruit set and fell during the exponential stage of growth to 1.05 μmol g⁻¹ fresh weight. During the second growth stage. PA and ABA levels remained stable and fell sharply at the beginning of maturation. The levels of spermidine and spermine decreased throughout fruit development and maturation from 0.61 to 0.05 and 0.31 to 0.02 μmol g⁻¹ fresh weight, respectively, but no changes were associated with the onset of maturation. ABA levels remained high (0.70-0.80 μg g⁻¹ fresh weight) during the stages of fruit growth and fell at the beginning of maturation to 0.12 μg g⁻¹ fresh weight, before rising again during the last stages of maturation and senescence. The decrease in putrescine and ABA levels and the subsequent increase in the latter may be responsible for controlling the processes of ripening in pepper fruit.     

Abscisic acid relationships in the chill-related dormancy mechanism in apple seeds

Abscisic acid (ABA) levels in seeds from three cultivars of apple (Malus domestica Borkh.) which have substantially different chilling requirements were investigated by gas chromatography mass-spectrometry selected ion monitoring (GCMS-SIM) during stratification. The ABA content of dormant unchilled seeds was similar in the three cultivars, suggesting no relationship between the chilling requirement of those seeds and their ABA status. That chilling is not related to ABA changes during stratification was confirmed by warm (20°C) and cold (5°C) stratification experiments. ABA content dropped rapidly and nearly identically under both temperature regimes, but only cold stratification promoted germination. The decline in ABA during stratification was due in large part to leaching from the seed coat and nucellar membrane; the ABA content of the embryo remained nearly constant. The radicle in intact seeds stratified at 5°C began growing 20–30 days after the ABA in the seed coat and nucellar membrane had nearly disappeared. Radicle growth did not occur in unchilled seeds, even though ABA had leached from them as well. It is possible that the leaching of ABA from the seed allows certain promotive forces to develop, but if so, these can develop only at chilling temperatures. Studies were also conducted on 2-trans ABA relationships to apple seed dormancy, but no association was evident.Report No. 12, Department of Fruit and Vegetable Science, Cornell University.