Seasonal changes in endogenous ABA and IAA and the influence of applied ABA and auxin in relation to shoot growth and abscission in Valencia Orange (Citrus sinensis (L.) Osbeck)

Seasonal changes in endogenous IAA and ABA were measured by gas chromatography/mass-spectrometry. Highest concentrations of ABA occurred in leaves. There was a major ABA peak in early spring (up to 1360 ng g^–1 dw). Levels were low in summer (90 ng g^–1 dw). There was a minor ABA peak in autumn. Endogenous IAA in leaves was highest in winter/spring (up to 76 ng g^–1 dw). Applied ABA promoted abscission of leaves and shoots while applied NAA delayed abscission. The main peak in leaf-ABA content was followed by extensive shoot abscission. The involvement of ABA and IAA in regulation of flush growth was not clear.This paper is dedicated to Michael G. Mullins, who died on 13 November 1990, for his outstanding contribution to horticulture.     

Hormonal changes in papaya seedlings subjected to progressive water stress and re-watering

Changes on abscisic acid (ABA), jasmonic acid (JA) and indole-3-acetic acid (IAA) levels were investigated in papaya seedlings (Carica papaya L.) cv. “Baixinho de Santa Amalia” under progressive water stress and subsequent rehydration. Also, the behaviour of leaf gas exchange and leaf growth was determined under stress condition. The results indicated that ABA and JA differ in their pattern of change under water stress. ABA continuously increased in leaves and roots during the whole period of stress whereas JA showed a sharp increase and a later decrease in both organs. Re-watering reduced rapidly (24 h) leaf and root ABA to control levels whereas the influence on JA levels could not be assessed. Drought and recovery did not alter IAA levels in leaf and root tissues of papaya seedlings. In addition, water stress reduced stomatal conductance, photosynthetic rate, transpiration rate, the percentage of attached leaves and leaf growth. Rehydration reverted in few days the effects of stress on leaf growth and gas exchange parameters. Overall, the data suggest that ABA could be involved in the induction of several progressive responses such as the induction of stomatal closure and leaf abscission to reduce papaya water loss. In addition, the pattern of accumulation of JA is compatible with a triggering signal upstream ABA. The unaltered levels of IAA could suggest a certain adaptive ability of papaya to maintain active physiological processes under progressive drought stress.     

Hormonal Regulation of Pedicel Abscission in Begonia Flower Buds

In order to analyse the hormonal regulation of flower bud shedding in Begonia, levels of indoleacetic acid (IAA), abscisic acid (ABA) and ethylene were determined in buds and pedicels. The translocation and metabolism of ¹⁴C-labeled IAA in pedicel segments were also studied. In a monoecious Begonia fuchsioides hybrid, abscising male flower buds contain about 1% of the IAA present in non-abscising female flowers. In a male Begonia davisii hybrid, the seasonal variation in bud drop coincides with changes in the IAA content of the buds, while also the release of IAA from the bud to the pedicel is hampered. Abscission zones of these pedicels always contain abscission promoting ethylene concentrations. The tissue is prevented from responding with abscission by IAA from the flower buds. The buds also contain ABA but without influencing abscission considerably. Pretreatment with ethylene or ABA does not affect IAA transport in pedicel segments. The rate of this transport is 4–6 mm × h^–1:; the capacity increases with the transverse area. In young segments, IAA is decarboxylated and also otherwise metabolized.     

Effects of pod removal on the transport and accumulation of abscisic Acid and indole-3-acetic Acid in soybean leaves

Concentrations of abscisic acid (ABA) and indole-3-acetic acid (IAA) in the second most recently expanded trifoliolate leaf were determined during reproductive development of soybean (Glycine max [L.] Merr cv `Chippewa 64'). The concentration of ABA in leaves was constant during most of the seed filling period until the seeds began to dry. The concentration of IAA in the leaves decreased throughout development. Removal of pods 36 hours prior to sampling resulted in increased concentrations of ABA in leaves during the period of rapid pod filling but had little effect on the concentration of IAA in leaves. ABA appears to accumulate in leaves after fruit removal only when fruits represent the major sink for photosynthate.

ABA and IAA moving acropetally and basipetally in petioles of soybean were estimated using a phloem exudation technique. ABA was found to move mostly in the basipetal direction in petioles (away from laminae). IAA, primarily in the form of ester conjugate(s), was found to be moving acropetally (toward laminae) in petioles. The highest amount of IAA ester(s) was found in petiole exudate during the mid and late stages of seed filling. Removal of fruits 36 hours prior to exudation reduced the amount of IAA ester recovered in exudate, suggesting that fruits were a source of the IAA conjugate in petiole exudate.

     

Physiology and Chemistry of Substances Accelerating Abscission in Senescent Petioles and Fruit Stalks

Senescent petioles of Coleus rehneltianus Berger. Phaseolus vulgaris L. cv. Saxa. Acer pseudoplatanus L., and senescent fruit stalks of Malus domestica Borkh. cv. Golden Delicious contain at least three abscission accelerating substances, which were isolated by extraction with methanol or with water and by diffusion into agar. They were purified by thin-layer chromatography and bioassayed in a special abscission test using Coleus explants. Two of these abscission accelerators could be conclusively identified by thin-layer chromatography and by gas chromatography as abscisic acid and xanthoxin. The third substance, which has acidic properties and is less polar than abscisic acid, could not be identified. The concentration and the absolute amount of abscisic acid in Coleus petioles were found to decrease during their development, young petioles having the highest concentration. No evidence was found that the three abscission accelerators or synthetic abscisic acid and xanthoxin affect the production of ethylene in Caleus explatns. The results obtained do not support the hypothesis that senescent petioles contain a specific “senescence factor”, which stimulates abscission via ethylene production.     

Leaf Abscission Induced by Ethylene in Water-Stressed Intact Seedlings of Cleopatra Mandarin Requires Previous Abscisic Acid Accumulation in Roots

The involvement of abscisic acid (ABA) in the process of leaf abscission induced by 1-aminocyclopropane-1-carboxylic acid (ACC) transported from roots to shoots in Cleopatra mandarin (Citrus reshni Hort. ex Tan.) seedlings grown under water stress was studied using norflurazon (NF). Water stress induced both ABA (24-fold) and ACC (16-fold) accumulation in roots and arrested xylem flow. Leaf bulk ABA also increased (8-fold), although leaf abscission did not occur. Shortly after rehydration, root ABA and ACC returned to their prestress levels, whereas sharp and transitory increases of ACC (17-fold) and ethylene (10-fold) in leaves and high percentages of abscission (up to 47%) were observed. NF suppressed the ABA and ACC accumulation induced by water stress in roots and the sharp increases of ACC and ethylene observed after rewatering in leaves. NF also reduced leaf abscission (7-10%). These results indicate that water stress induces root ABA accumulation and that this is required for the process of leaf abscission to occur. It was also shown that exogenous ABA increases ACC levels in roots but not in leaves. Collectively, the data suggest that ABA, the primary sensitive signal to water stress, modulates the levels of ethylene, which is the hormonal activator of leaf abscission. This assumption implies that root ACC levels are correlated with root ABA amounts in a dependent way, which eventually links water status to an adequate, protective response such as leaf abscission.     

Ethylene-induced leaf abscission in cotton seedlings : the physiological bases for age-dependent differences in sensitivity

The speed of ethylene-induced leaf abscission in cotton (Gossypium hirsutum L. cv LG-102) seedlings is dependent on leaf position (i.e. physiological age). Fumigation of intact seedlings for 18 hours with 10 microliters per liter of ethylene resulted in 40% abscission of the still-expanding third true (3°) leaves but had no effect on the fully expanded first true (1°) leaves. After 42 hours of fumigation with 50 microliters per liter of ethylene, total abscission of the 3° leaves occurred while <50% abscission of the 1° leaves was observed. On a leaf basis, endogenous levels of free IAA in 1° leaves were approximately twice those of 3° leaves. Free IAA levels were reduced equally (approximately 55%) in both leaf types after 18 hours of ethylene (10 microliters per liter) treatment. Ethylene treatment of intact seedlings inhibited the basipetal movement of [¹⁴C]IAA in petiole segments isolated from both leaf types in a dose-dependent manner. The auxin transport inhibitor N-1-naphthylphthalamic acid increased the rate and extent of ethylene-induced leaf abscission at both leaf positions but did not alter the relative pattern of abscission. Abscission-zone explants prepared from 3° leaves abscised faster than 1° leaf explants when exposed to ethylene. Ethyleneinduced abscission of 3° explants was not appreciably inhibited by exogenous IAA while 1° explants exhibited a pronounced and protracted inhibition. The synthetic auxins 2,4-D and 1-naphthaleneacetic acid completely inhibited ethylene-induced abscission of both 1° and 3° explants for 40 hours. It is proposed that the differential abscission response of cotton seedling leaves is primarily a result of the limited abscission-inhibiting effects of IAA in the abscission zone of the younger leaves.     

A Comparison of Abscission of Rubber (Hevea brasiliensis) Leaves Infected with Microcyclus ulei with Leaf Abscission Induced by Ethylene Treatment, Deblading and Senescence

Studies on the histology and on effects of growth substancesand phenols as well as changes in activities of pectinmethylesterase indicated that the mechanism of abscission of Hevealeaflets infected with Microcyclus ulei differed from the mechanismof abscission of debladed, ethylene treated and senescent leaves.An abscission layer which was formed during abscission of debladed,ethylene-treated and senescent leaves was absent during abscissionof heavily diseased leaves. The ratio of pectinmethyl esteraseactivities in tissues distal to the abscission zone to activitiesin tissues proximal to the zone decreased in debladed and ethylenetreated leaves but such decreases were not detected during abscissionof Hevea leaves infected with M. ulei. Hevea brasiliensis Muell. Arg., rubber, leaf abscission, Microcyclus ulei, ethylene, indol-3-ylacetic acid, kinetin     

Changes in Free and Conjugated Indole 3-Acetic Acid and Abscisic Acid in Young Cotton Fruits and Their Abscission Zones in Relation to Fruit Retention during and after Moisture Stress

Experiments were conducted with field-grown cotton (Gossypium hirsutum L.) in 1985 and 1986 to determine effects of water deficit on levels of conjugated indole 3-acetic acid (IAA) and abscisic acid (ABA) in young fruits (bolls) and their abscission zones in relation to boll retention. Tissues were harvested three times during an irrigation cycle in 1985. They were harvested twice during an irrigation cycle and once after irrigation in 1986 to determine extent of recoveries of measured parameters. As reported earlier, the free IAA content of abscission zones decreased with moisture stress. Irrigation caused a partial recovery in free IAA content of abscission zones and caused a partial recovery in rate of boll retention. In contrast to free IAA, conjugated IAA increased with water deficit, both in 3-day-old bolls and in their abscission zones. Bolls contained much more ester IAA than their abscission zones. Some, but not all, of the increase in ester IAA in bolls during moisture stress could have come from a conversion of amide-linked IAA. Amide IAA decreased slightly during stress and increased after irrigation, but the concentration was low relative to ester IAA. Free and conjugated ABA both increased during stress and decreased after irrigation. However, the concentration of conjugated ABA remained relatively high in abscission zones. Ester IAA, being more resistant than free IAA to enzymic destruction during stress, may hasten recovery of fruit retention after relief of stress by providing a source of free IAA in abscission zones to inhibit continued abscission.     

Auxin in scapes,flower buds,flowers, and fruits of daffodil (Narcissus pseudonarcissus L.)

Summary Diffusates from flower buds, flower fruits, and scape segments, and extracts of flower stalks of Narcissus pseudonarcissus contain an auxin active in the Avena geo-curvature test. The auxin behaved like indole-3-acetic acid (IAA) in thin-layer chromatography (TLC) with neutral and basic solvents on different adsorbents. After TLC, the auxin of the extracts showed chromogenic reactions identical with those of IAA; in gas-liquid chromatography on two different columns, the purified substance, after methylation, appeared at the retention time of IAA methyl ester. The auxin content of the extracts has been estimated to be equivalent to ca. 10 g IAA kg^–1 fresh weight. Diffusates, collected at the basal end of excised flowering apices and of scape segments at different developmental stages, showed highest auxin activity when collected from old buds and young flowers, and from the basal, rapidly elongating scape regions. The diffusible auxin obtained from scape segments was very likely produced by the segments themselves. Thus, the shoot of Narcissus appears to possess two different sites of auxin production, namely, the apical region represented by the flower bud, the flower or the fruit, and the scape.Abbreviations IAA indole-3-acetic acid - IAA-OMe indole-3-acetic-acid methyl ester - TLC thin-layer chromatography - GLC gas-liquid chromatography     

Abscisic Acid Metabolism in Relation to Water Stress and Leaf Age in Xanthium strumarium

Intact plants of Xanthium strumarium L. were subjected to a water stress-recovery cycle. As the stress took effect, leaf growth ceased and stomatal resistance increased. The mature leaves then wilted, followed by the half expanded ones. Water, solute, and pressure potentials fell steadily in all leaves during the rest of the stress period. After 3 days, the young leaves lost turgor and the plants were rewatered. All the leaves rapidly regained turgor and the younger ones recommenced elongation. Stomatal resistance declined, but several days elapsed before pre-stress values were attained.

Abscisic acid (ABA) and phaseic acid (PA) levels rose in all the leaves after the mature ones wilted. ABA-glucose ester (ABA-GE) levels increased to a lesser extent, and the young leaves contained little of this conjugate. PA leveled off in the older leaves during the last 24 hours of stress, and ABA levels declined slightly. The young leaves accumulated ABA and PA throughout the stress period and during the 14-hour period immediately following rewatering. The ABA and PA contents, expressed per unit dry weight, were highest in the young leaves. Upon rewatering, large quantities of PA appeared in the mature leaves as ABA levels fell to the pre-stress level within 14 hours. In the half expanded and young leaves, it took several days to reach pre-stress ABA values. ABA-GE synthesis ceased in the mature leaves, once the stress was relieved, but continued in the half expanded and young leaves for 2 days.

Mature leaves, when detached and stressed, accumulated an amount of ABA similar to that in leaves on the intact plant. In contrast, detached and stressed young leaves produced little ABA. Detached mature leaves, and to a lesser extent the half expanded ones, rapidly catabolized ABA to PA and ABA-GE, but the young leaves did not. Studies with radioactive (±)-ABA indicated that in young leaves the conversion of ABA to PA took place at a much lower rate than in mature ones. Leaves of all ages rapidly conjugated PA to PA-glucose ester. Furthermore, when half expanded leaves were stressed on the intact plant, their rate of ABA catabolism was enhanced, an effect not observed in the young leaves.

In conclusion, young leaves on intact Xanthium plants produce little stress-induced ABA themselves, but due to import and a low rate of catabolism accumulate more ABA and PA than mature leaves.

     

Indoleacetic acid, abscisic acid and phenolic substances during development of hazel leaves

The levels of indoleacetic acid (IAA), abscisic acid (ABA) and phenolic substances were measured monthly in leaves of hazel ( Corylus avellana L. cv. Negreta) in different stages of development from April till abscission in November. IAA and ABA were quantified by flame ionization detector gas-chromatography (GLC), and the total phenolic content by a colorimetric technique. During spring, IAA levels were the highest, coinciding with the greatest expansion of the leaves; after which IAA gradually decreased as the leaves became older, although minor increases were observed in July-August and November. The ABA level in hazel leaves was low throughout the period of leaf existence, with a maximum in July and a second increase in November, coinciding with the last month in which hazel bears leaves. The phenols of the neutral fraction showed a minimum in May and a pronounced increase in June, remaining at this level during summer and decreasing in November. The acid and alkaline fractions showed a maximum in August, which could be related to the decrease in the growth rate of leaves. The residual fraction remained at a relatively low level until September, increasing rapidly in October and November.     

Abscisic Acid Reduces Leaf Abscission and Increases Salt Tolerance in Citrus Plants

This paper describes the physiological effects of abscisic acid (ABA) and 100 mM NaCl on citrus plants. Water potential, leaf abscission, ethylene production, photosynthetic rate, stomatal conductance, and chloride accumulation in roots and leaves were measured in plants of Salustiana scion [Citrus sinensis (L) Osbeck] grafted onto Carrizo citrange (Citrus sinensis [L.] Osbeck × Poncirus trifoliata [L.] Raf) rootstock. Plants under salt stress accumulated high amounts of chloride, increased ethylene production, and induced leaf abscission. Stomatal conductance and photosynthetic rates rapidly dropped after salinization. The addition of 10 mM ABA to the nutrient solution 10 days before the exposure to salt stress reduced ethylene release and leaf abscission. These effects were probably due to a decrease in the accumulation of toxic Cl- ions in leaves. In non-salinized plants, ABA reduced stomatal conductance and CO2 assimilation, whereas in salinized plants the treatment slightly increased these two parameters. The results suggest a protective role for ABA in citrus under salinity.     

Effects of Age and Water Stress on Endogenous Levels of Plant Growth Regulators in Euphorbia lathyrus L.

The effect of droughting and waterlogging on changes in endogenouslevels of hormones have been studied in Euphorbia lathyrus L.with particular reference to plant age and leaf age. Younger tissues (i.e. immature leaves and young plants) synthesizedsignificantly greater amounts of ABA per unit fresh weight thandid corresponding older tissue. The increased ABA levels correlatedwell with corresponding increases in water saturation deficit(WSD) and stomatal resistance in a given treatment but the relationshipbetween the absolute values of these three parameters variedgreatly between seedlings of different ages. Endogenous ethylenelevels in leaves and stems were unaffected by droughting irrespectiveof age. Imposition of waterlogging led to marked increases in ABA levelsin young plants though this was not strictly related to changesin WSD or stomatal resistance. Endogenous levels of ethyleneincreased in response to waterlogging, this being marked inthe older seedlings which also had a higher incidence of senescenceand abscission. The more complex effects of waterlogging, the significance ofage of tissue on hormonal responses to stress, and the adaptivevalue of such responses to younger tissues are discussed.     

Changes in Abscisic Acid and Indoleacetic Acid before and after Anthesis Relative to Changes in Abscission Rates of Cotton Fruiting Forms

Cotton (Gossypium hirsutum L.) fruiting forms exhibit pronounced changes, with age, in their probability of abscission. Large floral buds rarely abscise, but after anthesis the young fruits (bolls) have a high probability of abscising. Abscission rate reaches a peak about 5 to 6 days after anthesis and then gradually decreases. An experiment was conducted to try to determine the reason for the rapid and pronounced increase in probability of abscission just after anthesis. Cotton was grown in the field and fruiting forms of various ages from 9 days before to 9 days after anthesis were all harvested the same day and subsequently analyzed for ABA and IAA. The concentration of ABA decreased slightly at anthesis and increased gradually thereafter. In contrast, the concentration of IAA was high before anthesis and then decreased at anthesis to about one-fifth the previous concentration. IAA remained low for at least 4 days after anthesis and then increased rapidly between 7 and 9 days after anthesis. The high concentration of IAA in floral buds before anthesis is probably a major factor in their resistance to abscission. Likewise, the low concentration of IAA at anthesis and for about 4 days thereafter may promote fruit abscission during the young boll stage.     

Effect of water stress on transport of [2-14C]abscisic acid in intact plants ofPhaseolus coccineus L.

Summary Eight- to 10-day-old plants ofPhaseolus coccineus, which grow on vermiculite with a water content of 12–17% of the water-holding capacity, stop growing completely, whereas water potential and relative water content are almost unaffected. [2-¹⁴C]Abscisic acid, which is applied to the midrib of a primary leaf, is transported especially to the roots and the apical bud, but not to the second primary leaf and the cotyledons. Water-stressed plants, however, export only negligible amounts of ABA from the donor leaf to the plant. Thus an accumulation of ABA occurs in the donor leaf. Consequently water stress can increase ABA concentration in leaves not only by stimulating ABA synthesis but also by inhibiting ABA transport. Recovery of growth and ABA transport after reirrigation is very weak. Water stress has no effect on ABA metabolism in bean plants.Abbreviations ABA abscisic acid - GA gibberellic acid - IAA indoleacetic acid - RWC relative water content in plants - TLC thin-layer chromatography     

Free fatty acids from the weed,Polygonum orientale leaves for attraction of the potential biocontrol agent,Galerucella placida (Coleoptera: Chrysomelidae)

Extraction, thin layer chromatography and gas chromatography-mass spectrometry of leaf surface waxes of Polygonum orientale L. (Polygonaceae) weed revealed 11, 15 and 11 free fatty acids in young, mature and senescent stages. Oleic acid was the predominant in young leaves (5950 ± 111 µg); whereas palmitic acid was the predominant fatty acids, representing 4247.5 ± 23 and 6644 ± 110 µg in mature and senescent leaves, respectively. Both tridecanoic and heneicosanoic acids were not detected in young and senescent leaves, and myristic and heptadecanoic acids were not identified in young leaves; whereas lauric and nonadecanoic acids were not detected in senescent leaves. The free fatty acids from young, mature and senescent weed leaves, and the mixtures of synthetic fatty acids mimicking free fatty acids of three types of weed leaves attracted female Galerucella placida (Coleoptera: Chrysomelidae) at the minimal amounts of 2, 1 and 2 leaf equivalent free fatty acids, respectively, in Y-shaped glass tube olfactometer bioassays under laboratory conditions. Individual synthetic pentadecanoic, palmitoleic, stearic, nonadecanoic and docosanoic acids at 44.82, 9.91, 92.22, 18.33 and 15.88 µg, respectively, elicited attraction of the insect. A synthetic blend of 3.59, 7.89, 44.82, 9.91, 32.31, 18.33 and 15.88 µg of lauric, myristic, pentadecanoic, palmitoleic, heptadecanoic, nonadecanoic and docosanoic acids, respectively, indicated highest attraction of the insect.     

Influence of water deficits on the abscisic Acid and indole-3-acetic Acid contents of cotton flower buds and flowers

A field experiment was conducted during the summer of 1988 to test the hypothesis that water deficit affects the abscisic acid (ABA) and indole acetic acid (IAA) concentrations in cotton (Gossypium hirsutum L.) flower buds in ways that predispose young fruits (bolls) that subsequently develop from them to increased abscission rates. Water deficit had little effect on the ABA content of flower buds but increased the ABA content of flowers as much as 66%. Water deficit decreased the concentrations of free and conjugated IAA in flower buds during the first irrigation cycle but increased them during the second cycle. Flowers contained much less IAA than buds. Water deficit slightly increased the conjugated IAA content of flowers but had no effect on the concentration of free IAA in flowers. Because water deficit slightly increased the ABA content but did not decrease the IAA content of flowers, any carry-over effect of water deficit on young boll shedding might have been caused by changes in ABA but not from changes in IAA.     

Quantitative determination of indole-3-acetic Acid in sugarbeet leaves using a double standard isotope dilution gas chromatographic assay

Quantitative levels of indole-3-acetic acid (IAA) were determined in leaf blades of two sugarbeet cultivars by a double standard isotope dilution assay using column chromatography followed by reverse phase C₁₈ high performance liquid chromatography and gas-liquid chromatography with nitrogen thermionic detection. The double standard method was validated as a quantitative tool by gas chromatography/selected ion monitoring mass spectrometry using 2,′,4′,5′,6′,7′-d₅-IAA as the internal standard. Progenies of one breeding line that had been selected for a high taproot to leaf weight ratio were used to correlate IAA levels with varying leaf and plant size at day 31 from germination. In spite of size differences, no significant difference in IAA levels per unit leaf weight could be found. The possible relationship between day 31 leaves and IAA content at an earlier stage of development is discussed in the text. A second analysis used four developmental leaf stages, classified as expanding, recently mature, aging, and senescing leaves. Expanding leaves contained the most IAA, senescing leaves contained the least IAA, with recently mature leaves and aging leaves containing intermediate amounts. The DNA content of each of the four developmental leaf stages was determined and DNA levels per gram fresh weight were found to be constant at all developmental stages.     

Interaction of abscisic acid and indole-3-acetic acid-producing fungi with Salix leaves

The molds Botrytis cinerea, Cladosporium cladosporioides, and the yeast Aureobasidium pullulans, isolated from the leaves of three short-rotation Salix clones, were found to produce indole-3-acetic acid (IAA). Abscisic acid (ABA) production was detected in B. cinerea. The contents of IAA and ABA in the leaves of the Salix clones and the amounts of fungal propagules in these leaves were also measured, in order to evaluate whether the amounts of plant growth regulators produced by the fungi would make a significant contribution to the hormonal quantities of the leaves. The content of ABA, and to a lesser degree that of IAA, showed a positive correlation with the frequency of infection by the hormone-producing organisms. The amounts of hormone-producing fungi on leaves that bore visible colonies were, however, not sufficiently high to support the claim that either the fungal production of ABA or IAA would significantly contribute to the hormonal contents of the leaves of the Salix clones. It is therefore suggested that the effect of fungal IAA production on plants is limited to the rhizosphere and that B. cinerea, which is a known pathogen, induces ABA production by the mother plant as a response to physiological stress.Abbreviations ABA abscisic acid - ABA-Me abscisic acid methyl ester - GC-MS-SIM gas chromatography-selected ion monitoring-mass spectrometry - IAA indole-3-acetic acid - IAA-Me indole-3-acetic acid methyl ester Author for correspondence.