Abscisic acid inhibition

Reversal of abscisic acid-inhibited betacyanin synthesis by phenolic compounds in Amaranthus caudatus seedlings. Physiol. Plant 58 175-178. 

Abscisic acid inhibits frond cell expansion in duckweed (Newton 1977), reducing both the increase in width and length of the developing frond. ABA has similar though somewhat weaker effects on Spirodela (Van Staden and Born-man 1970), and in both cases the inhibitory effects of ABA can be partially overcome by cytokinin (Van Overbeek et al. 1968, Van Staden and Bornman 1970). 

Pernet JJ, Pilet PE (1976) Indoleacetic acid movement in the root cap. Planta 128 183-184 Philipson JJ, Hillman JR, Wilkins MB (1973) Studies on the action of abscisic acid on lAA-induced rapid growth of Avena coleoptile segments. Planta 114 87-93 Phillips DA (1971) Abscisic acid inhibition of root nodule initiation in Pisum sativum. Planta 100 181-190... 

Abscisic acid inhibition of the translation of the germination mRNA preventing vivipary... 

Abscisic acid inhibited the a-amylase activities in an Aspergillus species and Bacillus subtilis. ... 

In Table 7 the effects of abscisic acid, lAA, gibberellins, and cytokinins on certain morphogenetic processes are contrasted with each other. The tabular summary has been considerably simplified. Nevertheless the principle is not affected by this. Abscisin counteracts the other phytohormones in quite different morphogeneses. Perhaps one and the same mechanism lies behind this diversity abscisic acid inhibits... 

Park SY et al (2009) Abscisic acid inhibits type 2C protein phosphatases via the PYR/PYL family of START proteins. Science 324 1068-1071... 

Downton, W.J.S., Loveys, B.R. Grant, W.J.R. (1988). Stomatal closure fully accounts for the inhibition of photosynthesis by abscisic acid. New Phytologist, 108, 263-6. 

Ward, D.A. Drake, B.G. (1988). Osmotic stress temporarily reverses the inhibitions of photosynthesis and stomatal conductance by abscisic acid - evidence that abscisic acid induces a localized closure of stomata in intact, detached leaves. Journal of Experimental Botany, 39, 147-55. 

The second example described here is dormant seeds from Rosa canina. Extracts of these seeds also inhibit germination of seeds of several plants (10). In Figure 5 a scheme is given for extraction and separation oF"three different inhibitor compounds. All these are present in the acid fraction. The first essential step is chromatography on Sephadex LH-20, which separates inhibitor I from inhibitor II and III. Inhibitor I was identified as abscisic acid. The other two inhibitors were separated by methylation with diazomethane, fractional distillation, and column chromatography. The second inhibitor is the a-pyrone 1 . Reaction with diazomethane transforms it into the bi-cyclic compound 19. This bicyclic compound is even more active than the parent a-pyrone 1 . Since we sought structural requirements for bioactivity here also,we tested several synthetic a-pyrones ( 0 - 22) for bioactivity. These compounds had no inhibitory activity. We alio tested the cyclopropane derivatives 23 and 24 In Table II, the bioactivity of the bicyclic compound T9 and two such derivatives is compared. The presence of several carboxylic acid groups seems to be essential (or at least helpful) for bioactivity in this case also. 

Roles of Metabolites of Abscisic Acid. Nothing is known about the physiological role of PA and DPA in plants, although these two metabolites of ABA have been tested in several bioassays recently. In the cotton explant abscission assay PA had one-tenth of the activity of ABA (19). PA and DPA were equally effective in inhibiting a-amylase secretion by barley aleurone layers treated with glbberellin A3 DPA had approximately one-tenth of the activity of ABA in this system (74). The effect of PA on growth of bean embryos was negligible (75). 

Ethylene and ABA. Abscisic acid (ABA), like ethylene, inhibits growth of etiolated seedlings but the seedlings do not show the triple response characteristic of ethylene-treated seedlings (36). ABA-inhibited pea seedlings produce less ethylene than seedlings not treated with ABA in response to high... 

Much like the phenolic acids, early work with scopoletin showed it inhibited oxidation of IAA and thus could affect growth in this manner. Inhibition of several other enzymes by scopoletin and coumarin has been shown. Coumarin was reported to induce ethylene synthesis.47 Also, it is one of several phenolic compounds that antagonize abscisic acid-induced inhibition of growth and stomatal closure.52 Undoubtedly, these and possibly other interactions with hormones are part of the physiological action of the coumarins. 

There are two important classes of allelochemicals synthesized by oxidative cleavages of tetraterpene carotenoids. One is the plant hormone abscisic acid (ABA, 31) that plays important roles in growth and development of plants, especially in seed development and dormancy.17 Dry dormant seeds contain relatively large amounts of ABA, particularly in the seed coats. ABA and phenolic allelochemicals in the seed coats are easily released into the environment when the seeds are imbibed, resulting in inhibition of seed germination and seedling growth of plants in the vicinity. Both ABA and the phenolic compounds are rapidly broken down in the soil, and therefore the inhibition is short-lived. 

Induction of de novo synthesis of a-amylase by GA in isolated aleurone layers is evident after a lag period of approximately 8 hr following administration of the hormone. In keeping with hormone responses generally, GA must be present continuously if the de novo synthesis of hydrolases is to be sustained. Synthesis of new RNA is essential to the GA-induction of de novo synthesis of hydrolases. Actinomycin D, an inhibitor of RNA synthesis, inhibits the synthesis and release of a-amylase if the inhibitor is presented during the first 7 to 8 hr after treatment. Inhibitors of protein synthesis, such as cycloheximide, also inhibit GA-induction of hydrolases. And, interestingly, abscisic acid, a growth-inhibiting hormone, inhibits GA-induced a-amylase synthesis as well. 

The mechanism of action of abscisic acid (ABA) has been studied to the greatest extent in the barley aleurone system (29), in which ABA counteracts the effect of GA in the induction of hydrolases. This action of ABA has largely been the basis for speculating that ABA may act specifically to inhibit, by some unknown mechanism, DNA-dependent RNA synthesis. Much evidence indicates that ABA acts at the transcriptional level, but it also has been proposed that the inhibition of induction of a-amylase synthesis is caused, at least in part, by an effect on translation because ABA still inhibited the formation of a-amylase at 12 hr when cordycepin (an inhibitor of RNA synthesis) no longer had an effect (30). 

Figure 3. Model of the mode of action of auxin herbicides in the induction of growth inhibition, tissue damage and senescence in dicot plant species, as illustrated for cleavers Galium aparine). ABA, abscisic acid ACC, 1 -aminocyclopropane-1 -carboxylic acid ROS, reactive oxygen species SAM, S-adenosylmethionine. Modified fiom [20,41],...

The photosynthetic efficiency mainly depends on the openness of stomata, particularly in C3 crops, while their closure tends to avoid excessive water loss. Abscisic acid (ABA) mediates water loss from the guardian cells of the stomata, which is triggered by a decrease in the water content of the leaf and inhibits leaf expansion. In muskmelon seedlings, ABA could improve the maintenance of the leaf water potential and relative water content, and reduce electrolyte leakage [55]. 

At times when a plant needs to slow down growth and assume a resting stage (dormant), abscisic acid is produced in the terminal bud, which slows down growth and directs the leaf primordia to develop scales that protect the dormant bud during winter. Since the hormone also inhibits cell division in the vascular cambium, both primary and secondary growth is put on hold during winter. 

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