Activity and metabolism of C-(+/-)-abscisic Acid derivatives

Several radioactive analogues of abscisic acid have been tested for their growth-inhibitory effects and their metabolism in excised embryonic axes of Phaseolus vulgaris. The compounds tested were the methyl and ethyl esters of 2-¹⁴C-abscisic acid and the cis- and trans-1′,4′-diols of 2-¹⁴C-abscisic acid. All four compounds cause less growth inhibition than abscisic acid, and all four compounds are converted to abscisic acid in the axes at rates which are sufficient to account for most, if not all, of the observed growth-inhibitory activity. None of the four compounds is metabolized to the extent that abscisic acid is metabolized in the axes, suggesting that the structural requirements for growth-inhibitory activity and metabolism may be similar.     

Metabolism of 2-C-(+/-)-abscisic Acid in excised bean axes

Excised embryonic bean axes (Phaseolus vulgaris, var. White Marrowfat) rapidly metabolize 2-¹⁴C-(±)-abscisic acid to two compounds, M-1 and M-2, which have very low growth-inhibitory activity. Chemical tests indicate the M-1 and M-2 are not previously described abscisic acid metabolites. M-2 accumulates in the axes and evidence is presented for the hypothesis that abscisic acid → M-1 → M-2. Zeatin, which partially reverses the abscisic acid-mediated growth inhibition of axes, neither decreases abscisic acid uptake nor causes any major changes in its metabolism. It was observed that axes transferred from abscisic acid-containing solutions to buffer resume control rates of fresh weight increase while still containing considerable quantities of abscisic acid.     

Rapid growth inhibition of Avena coleoptile segments by abscisic Acid

An angular position sensing transducer was used to make continuous measurements of elongation of a column of Avena sativa coleoptile segments. Elongation stimulated by 2 μm indoleacetic acid was inhibited by 0.1 mm abscisic acid with a latent period of about 4 or 5 minutes at pH 6.0, 30 C. Full growth inhibition was not established until about 1 hour after the addition of the abscisic acid. The same degree of final growth inhibition could be obtained under the above conditions using 10 μM and 1 μM abscisic acid, but the latent period was longer. Pretreatments with abscisic acid affected the growth rate but did not extend the latent period of a subsequent response to auxin. The short term kinetics of inhibition by abscisic acid were not similar to those of any of the inhibitors of RNA and protein synthesis tested in this system.     

Growth Regulators Have Rapid Effects on Photosynthate Unloading from Seed Coats of Phaseolus vulgaris L

Of nine plant growth regulators (indoleacetic acid, 1-naphthalene acetic acid, gibberellic acid, giberellin 4/7, 6-benzylaminopurine, 6-furfurylaminopurine, abscisic acid, and 1-aminocyclopropane carboxylic acid) tested, only 6-benzylaminopurine and abscisic acid affected ¹⁴C-photosynthate unloading from excised seed coats of Phaseolus vulgaris L. Unloading, in the presence of KCl, was stimulated by 25 to 40%. Stimulation occurred immediately for 6-benzylaminopurine and for abscisic acid within 10 to 12 minutes of application.     

Water deficit-induced changes in abscisic Acid, growth, polysomes, and translatable RNA in soybean hypocotyls

Soybean seedlings (Glycine max L.) were germinated and dark-grown in water-saturated vermiculite (water potential = −0.01 megapascal) for 48 hours, then transferred either to water-saturated vermiculite or to low water potential vermiculite (water potential = −0.30 megapascal). A decrease in growth rate was detectable within 0.8 hour post-transfer to low water potential vermiculite. A fourfold increase in the abscisic acid content of the elongating region was observed within 0.5 hour. At 24 hours post-transfer, hypocotyl elongation was severely arrested and abscisic acid reached its highest measured level: 3.7 nanograms per milligram dry weight (74-fold increase). A comparison of the polyA⁺ RNA populations isolated at 24 hours post-transfer from the elongating region of water-saturated and low water potential vermiculite-grown seedlings was made by two-dimensional (isoelectric focusing-sodium dodecyl sulfate) polyacrylamide gel analysis of in vitro translation products. It revealed both increases and decreases in the relative amounts of a number of translation products. Rewatering seedlings grown in low water potential vermiculite at 24 hours post-transfer led to a total recovery in growth rate within 0.5 hour, while abscisic acid in the elongating hypocotyl region required 1 to 2 hours to return to uninduced levels. Application of 1.0 millimolar (±) abscisic acid to well-watered seedlings resulted in a 48% reduction in hypocotyl growth rate during the first 2 hours after treatment. Plants treated with abscisic acid for 24 hours had a lower polysome content than control plants. However, hypocotyl growth inhibition in abscisic acid-treated seedlings preceded the decline in polysome content.     

Abscisic Acid Content and Stomatal Sensitivity to CO(2) in Leaves of Xanthium strumarium L. after Pretreatments in Warm and Cold Growth Chambers

The degree of stomatal sensitivity to CO₂ was positively correlated with the content of abscisic acid of leaves of Xanthium strumarium grown in a greenhouse and then transferred for 24 hours or more to a cold (5/10 C, night/day) or a warm growth chamber (20/23 C). This correlation did not exist in plants kept in the greehouse continuously (high abscisic acid, no CO₂ sensitivity), nor in plants transferred from the cold to the warm chamber (low abscisic acid, high CO₂ sensitivity). The abscisic acid content of leaves was correlated with water content only within narrow limits, if at all. At equal water contents, prechilled leaves contained more abscisic acid than leaves of plants pretreated in the warm chamber. There appear to be at least two compartments for abscisic acid in the leaf.     

Vitamin E and defense-related phytohormones are reliable markers of embryo growth in macaw palm fruits exposed to various storage conditions

The fruit of the macaw palm (Acrocomia aculeata) may be used for biofuel production, but its exploitation as a crop is currently limited by its low germinability. Therefore, obtaining plantlets in vitro is an excellent way to solve this problem. Here we aimed to identify the optimal conditions for storing the fruit before obtaining plantlets and testing to what extent vitamin E and defense-related phytohormones are good indicators of embryo growth in vitro. We tested the effects of four storage conditions (nursery, laboratory, cold chamber and freezer) on seed germinability and embryo growth, and evaluated endogenous levels of vitamin E and defense-related phytohormones (abscisic acid, salicylic acid and jasmonic acid) in the endosperm and embryos. Low temperatures [both cold chamber (5 °C) and freezer (?18 °C) methods] killed the embryos, while storing the fruit in the laboratory was the most efficient method of obtaining plantlets, even after a year. Vitamin E and abscisic acid turned out to be good indicators of embryo growth. Enhanced vitamin E and abscisic acid levels had a strong positive correlation with successful embryo growth, thus indicating that these compounds are needed to protect the embryo during fruit storage. Furthermore, abscisic acid levels had a negative correlation with the percentage of contaminated embryos, thus suggesting that the endogenous physiological stage of the seeds affects subsequent contamination in in vitro cultures. We concluded that (1) storing fruit under laboratory conditions is the most efficient means of obtaining plantlets successfully, and (2) vitamin E and abscisic acid can be used as reliable indicators of embryo growth during in vitro culture.     

Abscisic Acid and the Photoperiodic Induction of Dormancy in Salix viminalis L

A series of growth room experiments was carried out aiming to establish the role of abscisic acid on dormancy of Salix viminalis L. The inhibitor content and abscisic acid levels of extracts from roots, sap, leaves, and apical tissues of willow were measured using biological assay and gas-liquid chromatography.     

Abscisic Acid: correlations with abscission and with development in the cotton fruit

Abscisic acid was measured in developing cotton fruit (Gossypium hirsutum) by means of gas-liquid chromatography. High levels of abscisic acid occurred in correlation with abortion and abscission of young fruit, with low germination of immature seed, and with senescence and dehiscence of mature fruit. Declining or low levels of abscisic acid occurred in correlation with the period of most rapid fruit growth and with high germination of immature and mature seed. Young fruit of cultivar Acala 4-42 contained about twice as much abscisic acid as young fruit of cultivar Acala SJ-1, and this difference is correlated with a higher rate of young fruit abscission in Acala 4-42. Young fruit abscising late in the fruiting season contained about twice as much abscisic acid as young fruit abscising early in the fruiting season.     

Inhibition of Low pH-induced Elongation in Avena Coleoptiles by Abscisic Acid

An angular position-sensing transducer was used to make continuous measurements of acid-induced elongation of Avena sativa coleoptile segments. Elongation rates at pH 4.5 (5 mm succinate buffer) were about 5-fold greater than those at pH 6.0. Buffered 0.1 mm abscisic acid produced a partial decrease of the growth rate. Pretreatments with abscisic acid buffered at pH 6.0 usually caused a further reduction of the elongation response when the coleoptile segments were subsequently placed in buffer at pH 4.5 containing abscisic acid. Abscisic acid did not completely prevent the pH effect in any of these experiments, and the brief latent period of the pH response was not affected by abscisic acid treatments. At pH 4.5, where the inhibitory effect of ABA was maximum, low pH-induced elongation was also inhibited by KCN and HgCl₂. These results suggest that pH-(4.5) induced elongation in this system may be dependent on some metabolic processes and that abscisic acid-induced inhibition of this elongation may involve an interaction with these processes.     

Effect of abscisic acid and cytokinins on cultured zygotic embryos of Coffea arabicacv.Cauvery (Catimor)

Immature zygotic embryos of Coffea arabica L.cv.Cauvery (Catimor) were sequentially cultured on different modifications of Murashige and Skoog's (MS) medium to test the effect of abscisic acid and cytokinins. The type of response depended on the medium strength, the growth regulator combinations as well as the period of initial culture in both abscisic acid or cytokinin supplemented media. Increasing concentration of abscisic acid from 0.4 to 18.9 μM enhanced the quiescence of the zygotic embryos. All the cytokinins promoted germination but Kinetin and isopentenyladenine (2-IP) were less effective than benzyl amino purine (BAP). The maximum mature embryos were obtained when immature embryos were cultured initially for 30 days on full strength MS medium with 3.8 μM ABA, followed by 60 days on half strength MS medium with 0.1 μM BAP and finally on half strength MS media with out growth regulator for next 60 days.     

Cytokinin Reversal of Abscisic Acid Inhibition of Growth and α-Amylase Synthesis in Barley Seed

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^?5M nearly completely inhibited growth response and α-amylase synthesis in barley seed. Kinetin reversed to a large extent abscisic acid inhibition of α-aniylase synthesis and coleoptile growth. The response curves of α-amylase synthesis and coleoptile growth in presence of a fixed amount of abscisic acid (6 × l0^?6M) and increasing concentrations of kinetin (from 5 × l0^?7M 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.     

Influence of Nitrogen Source, Thiamine, and Light on Biosynthesis of Abscisic Acid by Cercospora rosicola Passerini

Abscisic acid production by Cercospora rosicola Passerini in liquid shake culture was measured with different amino acids in combination and singly as nitrogen sources and with different amounts of thiamine in the media. Production of abscisic acid was highest with aspartic acid-glutamic acid and aspartic acid-glutamic acid-serine mixtures as nitrogen sources. Single amino acids that supported the highest production of abscisic acid were asparagine and monosodium glutamate. Thiamine was important for abscisic acid production. Leucine inhibited abscisic acid production. C. rosicola produced abscisic acid in the dark, but production more than doubled in the presence of light.     

Abscisic Aldehyde Is an Intermediate in the Enzymatic Conversion of Xanthoxin to Abscisic Acid in Phaseolus vulgaris L. Leaves

The enzymatic conversion of xanthoxin to abscisic acid by cell-free extracts of Phaseolus vulgaris L. leaves has been found to be a two-step reaction catalyzed by two different enzymes. Xanthoxin was first converted to abscisic aldehyde followed by conversion of the latter to abscisic acid. The enzyme activity catalyzing the synthesis of abscisic aldehyde from xanthoxin (xanthoxin oxidase) was present in cell-free leaf extracts from both wild type and the abscisic acid-deficient molybdopterin cofactor mutant, Az34 (nar2a) of Hordeum vulgare L. However, the enzyme activity catalyzing the synthesis of abscisic acid from abscisic aldehyde (abscisic aldehyde oxidase) was present only in extracts of the wild type and no activity could be detected in either turgid or water stressed leaf extracts of the Az34 mutant. Furthermore, the wilty tomato mutants, sitiens and flacca, which do not accumulate abscisic acid in response to water stress, have been shown to lack abscisic aldehyde oxidase activity. When this enzyme fraction was isolated from leaf extracts of P. vulgaris L. and added to extracts prepared from sitiens and flacca, xanthoxin was converted to abscisic acid. Abscisic aldehyde oxidase has been purified about 145-fold from P. vulgaris L. leaves. It exhibited optimum catalytic activity at pH 7.25 in potassium phosphate buffer.     

Abscisic Acid increases terrestrial plant cell resistance to hydrostatic pressure

Cells of the terrestrial plant species bromegrass (Bromus inermis L.) are not naturally adapted to withstand the hydrostatic pressures encountered in aquatic environments. However, after treatment with the natural plant growth hormone abscisic acid (75 micromolar), bromegrass cells survived a hydrostatic pressure of 101.3 megapascals, approximating the limits of ocean depth (10,860 m). The increased resistance to hydrostatic pressure from 1 to 7 days of abscisic acid treatment paralleled the induced elevation of cell tolerance to freezing stress.     

长白落叶松激素含量与生长的关系及在早期选择中的应用

用间接酶联免疫吸附法测定了不同季节不同种源长白落叶松激素含量。结果表明：不同季节长白落叶松的激素含量不同,速生期长白落叶松赤霉素、生长素和细胞分裂素含量高,脱落酸含量低,赤霉素／脱落酸比值大,生长缓慢期测定结果恰好相反。各类激素含量在不同种源长白落叶松间的变异显著,且与生长性状的差异密切相关。生长快的种源赤霉素,细胞分裂素含量高,脱落酸含量低,赤霉素／脱落酸之比大。生长慢的种源则相反。回归分析表明     

Relationship between Mefluidide Treatment and Abscisic Acid Metabolism in Chilled Corn Leaves

Mefluidide, N-(2,4-dimethyl-5[([trifluoromethyl]sulfonyl) amino] phenyl)acetamide, a synthetic plant growth regulator, was capable of triggering an increase in endogenous free abscisic acid content when corn (Zea mays L.) plants were grown in a nonstress, day/night, temperature regime (26°C) with sufficient moisture supply. The relevance of such an abscisic acid increase prior to chilling exposure and the water relations during chilling are discussed in reference to the mefluidide protection of the chilled corn plants.     

Abscisic Acid and stomatal regulation

The closure of stomata by abscisic acid was examined in several species of plants through measurements of CO₂ and H₂O exchange by the leaf. The onset of closure was very rapid, beginning at 3 minutes from the time of abscisic acid application to the cut base of the leaf of corn, or at 8 or 9 minutes for bean, Rumex and sugarbeet; rose leaves were relatively slow at 32 minutes. The timing and the concentration of abscisic acid needed to cause closure were related to the amounts of endogenous abscisic acid in the leaf. Closure was obtained in bean leaves with 8.9 picomoles/cm². (+)-Abscisic acid had approximately twice the activity of the racemic material. The methyl ester of abscisic acid was inactive, and trans-abscisic acid was likewise inactive. The effects of stress on levels of endogenous abscisic acid, and the ability of very small amounts of abscisic acid to cause rapid closure suggests that stomatal control is a regulatory function of this hormone.     

Abscisic Acid and Ethylene Increase in Heterodera avenae-infected Tolerant or Intolerant Oat Cultivars

The relationship between root stunting caused by the cereal cyst nematode and levels of two root growth inhibiting hormones, abscisic acid and ethylene, was investigated in aseptically cultured root segments and in intact roots of two oat cultivars differing in tolerance to the nematode. Cultured root segments of oat cultivars New Zealand Cape (tolerant) and Sual (intolerant) were inoculated with sterilized Heterodera avenae second-stage juveniles. Suppressed growth of root axes and emerged laterals following nematode penetration corresponded to an increase in abscisic acid and ethylene in roots of both intolerant and tolerant cultivars. When the experiment was repeated on intact root systems, nematodes retarded root growth of Sual more than New Zealand Cape despite an increase in ABA and ethylene in both cultivars. Abscisic acid and (or) ethylene may be involved in growth inhibition of H. avenae-infected roots but appear to play no direct role in determining tolerance.     

A water potential threshold for the increase of abscisic Acid in leaves

A relationship between abscisic acid concentration and leaf water status is reported. Water potentials were measured in leaves of Ambrosia artemisiifolia L. and Ambrosia trifida L. throughout a period of dehydration of intact plants. Tissues from the same leaves were analyzed for abscisic acid. For both species, abscisic acid began to increase in a critical water potential range (−10 to −12 atmospheres). These data suggest a threshold water potential that stimulates abscisic acid synthesis. The data support the hypothesis that a small change in water potential could affect stomatal resistance to water loss by means of a very sensitive chemical feedback control mechanism.