Abscisic acid synthesis

Zeevaart JAD (1977) Sites of abscisic acid synthesis and metabolism in Ridnus communis. Plant Physiol 59 788-791... 

Abscisic acid synthesis in the ovule tissue and its absorption by the embryo... 

Carotenoid catabolic products also have a physiological role in the plant. Oxidative cleavage of carotenoids by carotenoid cleavage dioxygenases (CCDs) generates apocarotenoids [21]. Apocarotenoids serve the plant as antifungal agents or in the synthesis of flavor or aroma of flowers and fruits. A well-known downstream product of an apocarotenoid is abscisic acid (ABA), a phytohormone in plants [21]. 

When subjected to drought stress, excised wheat Triticum aestivum L.) leaves increase ethylene production as a result of an increased synthesis of ACC 71 and an increased activity of the ethylene-forming enzyme (EFE) which catalyzes the conversion of ACC 71 to ethylene. Rehydratation to relieve water stress reduces EFE activity to levels similar to those in non-stressed tissue. Pretreatment of the leaves with N-benzyladenine (BA) 75 or indole-3-acetic acid lAA 76 prior to drought stress caused further increase in ethylene production. Conversely, pretreatment of wheat leaves with abscisic acid ABA 77 reduced ethylene production to levels of non-stressed leaves, accompanied by a decrease in ACC 71 content, Eq. (29). 

D-glucopyranosyl esters of abscisic acid and /3-ionylideneacetic acid (120) have been prepared by treatment of the acid with a-acetobromoglucose in the presence of triethylamine/ Two papers " describe a new synthesis of y-ionone (64) in which the key intermediate (121) is prepared from y-cyclocitral (122) and acetone in the presence of BU2BSO3CH2CF3. 

Abscisic acid, as the name suggests, has been implicated in the control of abscission of leaves, flowers and fruits, as well as with the function of stomata in response to water stress (Figure 5.4). Abscission involves the synthesis of cellulase in the ageing process and it is thought that abscisic acid influences the rate at which this proceeds. 

Violaxanthin also functions as a precursor to the plant hormone abscisic acid. Compare the structure of the latter (Fig. 22-4) with those of carotenoids. Oxidative cleavage of violaxanthin or related epoxy-carotenoids initiates the pathway of synthesis of this hormone.142 143... 

Smart, C.C. Trewavas, A.J. (1984). Abscisic-acid-induced turion formation in Spirodela polyrrhiza L. III. Specific changes in protein synthesis and translatable RNA during turion development. Plant, Cell and Environment 7, 121-32. 

Robertson, A.J., Gusta, L.V., Reaney, M.J.T. Ishikawa, M. (1987). Protein synthesis in bromegrass (Bromus inermis Leyss) cultured cells during the induction of frost tolerance by abscisic acid or low temperature. Plant Physiology 84, 1331-6. 

Abscisic acid is a negative regulator in that it primarily antagonizes the action of cytokinins, auxins, and in particular, gibberellins. Abscisic acid decreased the activity of polymerase in radishes (52), peas (53), maize coleoptiles (54), and pear embryos (55). More detailed studies are needed before the question of ABA-induced "modification" of RNA polymerase (54) or "alterations" in the number of sites for template activity (56) can be answered. In barley aleurone cells, ABA-induced suppression of GA-induced <-amylase formation was presumed to involve the continuous synthesis of a short-lived RNA (57). 

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. 

Minocha, S.C., Abscisic acid promotion of cell division and DNA synthesis in Jerusalem artichoke tuber tissue cultured in vitro, Z. Pflanzenphysiol., 92, 327-339, 1979. 

Neoxanthin, a precursor of the plant hormone abscisic acid, is an allenic xantho-phyll recognized as the last product of carotenoid synthesis in green plants. A cDNA for neoxanthin synthase (NSY) was isolated from tomato cv. Philippino using a molecular approach based on the mechanistic and structural similarities of NSY to two other closely related carotenogenic enzymes, lycopene cyclase (LCY) and capsanthin-capsorubin synthase (CCS) (Bouvier et al., 2000). 

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). 

Nigaki alcohol (18) has been identified by spectroscopic and chemical means as a constituent of Picrasma ailanthoides Planchon. Latia luciferin (19) has been synthesized in a stereoselective manner. A key step in this synthesis involves the addition of lithium dimethylcuprate to an enol phosphate derived from a 8-keto-ester to form an a,/3-unsaturated ester. Dehydro-/8-ionilideneacetic acid (20), an important intermediate in the synthesis of abscisic acid, has been prepared, as have the two nor-abscisic acid derivatives (21). The metabolite (22) of abscisic acid has been identified in the seeds of Robinia pseudacacia... 

The synthesis of optically active carotenoidshas been extended to include the preparation of important possible carotenoid metabolites such as (4-)-abscisic acid (126), (-)-xanthoxin (127), (-)-loliolide (128), (-)-actinidiolide (130), and (-)-dihydroactinidiolide (129), all from one starting compound... 

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