Abscisic acid formation

Milborrow, B. V. Stereochemical aspects of the formation of double bonds in abscisic acid. Biochem. J. 128, 1135—1146 (1972). 

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. 

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). 

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). 

Smolenska-Sym, G., and Kacperska, A., 1996, Inositol 1,4,5-trisphosphate formation in leaves of water oilseed rape plants in response to freezing, tissue water potential and abscisic acid. Physiol. Plant 96 692-698. 

The relationship between catabolite repression by glucose and induction of cellulase by sophorose has been studied in T. viride by Nisizawa and co-workers (36, 37). The induction by sophorose (10 M) was competitively repressed by glucose and other metabolites such as pyruvate. Since glucose was an effective repressor when added one hour after the previous addition of actinomycin D, it was concluded that the repression takes place at the translational level. Previous work indicated (26) that the sophorose induction led to the formation of a cellulase component designated FII, which is the source of cellulase II discussed below. In higher plants indoleacetic acid (38) and abscisic acid (39) have been shown to stimulate cellulase production. 

The 1,1-didesmethyl analogue (181) of abscisic acid (23) has been prepared.110 The cis-trans photoisomerization of (23) has been studied.111 A convenient procedure has been developed for the catalytic hydrogenation of p-ionone (142) to the m-5,6-dihydroionone (182).112 On treatment with Me2S+ CH, p-ionone gave the epoxide (183), which with MgBr2 afforded the aldehyde (184) without halohydrin formation.113... 

Abscisic acid (ABA) levels in rice plants, 308,31Or levels in squash hypocotyls, 315/.316 Active component of brassins identification, 9,lQf pilot plant extraction, 6,7/,8 solvent partition and column chromatography, 8 Adventitious root(s) development, 233,234r,235 formation, 247 Agriculture, application of 24-epibrassinolide, 280-290 22-Aldehydes, synthesis of brassinosteroids, 47-50f a hormone function, description for brassins, 4... 

Two compounds common in plant metabolism are believed to be precursors of isoprenoid cytokinins in plants adenosine-5 -monophosphate (AMP) and A -isopentenylpyrophos-phate (iPP). As a final product of the mevalonate pathway, the latter substance serves also as a precursor for a wide spectrum of metabolites including some other plant hormones, as abscisic acid, gibberellins and brassinosteroids. The hypothetical scheme of reactions resulting in the formation of iPA, Z and DHZ is given in Fig. 2. The enzyme of entry into isoprenoid cytokinin formation is A -isopentenylpyrophosphate 5 -AMP-A -iso-pentenyltransferase (EC 2.5.1.8, trivially named cytokinin synthetase ). This enzyme activity was first detected in a cell-free preparation from the slime mould Dictyostelium discoideum [7,8]. Later the enzyme from higher plants (cytokinin-independent tobacco callus [9,10] and immature Zea mays kernels [11]) was described and the data were recently summarised in [12], The enzyme is very specific as far as the substrate is concerned [13,14] only the nucleotide AMP can be converted and only iPP (with a double bond in A position) may function as a side chain donor. 

I04"C) is often considered as a plant growth substance because it acts like a fruit-ripening hormone. The biosynthesis of ethylene in the plant from 1 -ami-nocyclopropanecarboxylic acid is stimulated by auxins abscisic acid and cytokinins can - depending on the type of plant - have stimulating or inhibiting effects, and tissue injuries in plants lead to the formation of the so-called wound ethylene . For information on the numerous roles of ethylene, see Other... 

Poly(c -l,4-isoprene) belongs to the family of polyisoprenoids, which are the most structurally diverse and abundant natural products known, with more than 23,000 primary and secondary metabolites. This huge family comprises, for example, sterols which display not only structural functions (control of biological membrane fluidity) but also hormonal functions (steroid hormones). Key phyto-hormones, such as abscisic acid, gibberellins and cytokinins, are isoprenoids too. Moreover, isoprenoids are used in protein prenylation, which is a key step in the activation and the localization of metabolic enzymes in many organisms. The first common step of all isoprenoid biosynthesis pathways is the formation of isopentenyl diphosphate (IPP). ... 

Thus, cell enlargement, for instance, depends upon auxin and involves the uptake of water, extension of the cell membrane and protein synthesis. The auxin dose-response curve consists of two peirts promotion by low concentrations and inhibition by higher concentrations via the formation of ethylene. Cytokinins and abscisic acid may possibly induce also, under special conditions, the production of ethylene. Many publications deal with effects of these plant hormones, especially of auxin, on ethylene biosynthesis in plants which occurs after a lag phase of 30 - 60 minutes and is specifically blocked by rhizobitoxin as well as by inhibitors of ENA and protein synthesis indicating that a continuous synthesis of protein is required for high rate of ethylene production (Eef. 20). 

Secondary metabolites, produced by pathways derived from primary metabolic routes, are numerous and widespread, especially in higher plants. More than 20,000 were known in 1985 (Hartmann, 1985), and at least 1000 additional compounds, are described each year. In practice, the difference between the primary and secondary metabolites is fuzzy. Plant hormones such as gibberellic acid, indoleace-tic acid (auxin), ethylene, kinetin, and abscisic acid, as well as compounds involved in plant cell wall structure such as cinnamic acid and its polymeric derivative, lignin, are intermediate between primary and secondary metabolism (Birch, 1973). In some instances, compounds normally considered primary metabolites may accumulate in large amounts and behave in a manner usually associated with secondary metabolites. Entities such as shikimic acid and squalene, which initially were considered secondary metabolites, were subsequently shown to be important intermediates in the formation of primary metabolites (phenylalanine, tyrosine and tryptophan, and steroids, respectively). 

In an indirect manner, the lipoxygenase reaction in higher plants appears to be implicated in the biosynthesis of abscisic acid, a further senescence hormone [23-25], Abscisic acid is formed from the carotenoid violaxanthin that is converted into xanthoxin, which is a plant growth inhibitor and at the same time a precursor of abscisic acid. The formation of xanthoxin requires the co-oxidative activity of a lipoxygenase-linoleic (or a-linolenic) acid system. 

Epoxidation of zeaxanthin by zeaxanthin epoxidase (ZE) would result in the production of violaxanthin via antheraxanthin. From that substrate, the enzyme neoxanthin synthase (NXS) would yield neoxanthin opening the cyclohexenyl 5-6 epoxide ring in violaxanthin [38]. Neoxanthin would be the last product of carotenoid biosynthesis in green parts of the plant, and it would derive in the abscisic acid (ABA) synthesis pathway. The accumulation of neoxanthin and violaxanthin in flowers results in wildtype yellow petals. A defective mutation in the gene encoding CRTR-B2 prevents formation of these xanthophylls, resulting in the white-flower phenotype [18]. 

Altman A, Goren R (1971) Promotion of callus formation by abscisic acid in citrus bud cultures. Plant Physiol 47 844-846... 

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