Abscisic acid kinetin

Matthyssee and Phillips (20) isolated two nuclear proteins, from tobacco cells, that bound specifically to 2,4-D. Receptor proteins for auxins, kinetins, and GA have been found (21). Sub-cellular fractions from bean leaves were recently shown to bind abscisic acid (22). Preliminary experiments (22) indicated that maximum ABA binding activity coincides with the activities of membrane-bound Mg -dependent, K+-stimulated ATPase and glucan synthetase. Table I of Biswas and Roy (21) lists hormone receptor proteins reported in plant tissue. For a protein to qualify as a receptor molecule, it should have a high stereo-specific binding capacity (Kd 10 6 to 10 SM) for its particular hormone. In com coleoptiles, both IAA and NAA are equally effective in inducing cell elongations fractions of plasma membrane and endoplasmic reticular membrane contain receptor proteins with Kd values of 10 M to 10 M for auxins (5, 18). When one considers procedural... 

Classically, there are five main categories of naturally occurring PGR, the auxins (lAA, NAA, IBA, 2,4-dichlorophenoxyacetic add), gibbereHins (GA), cytoM-nins (kinetin, benzyladenin, zeatin), ethylene, and growth inhibitors like abscisic acid (ABA). 

The related substance xanthoxin (4.88) clearly plays a fundamental part in normal plant regulation by antagonizing indolylacetic acid, gibberellic acid, and kinetin. It is readily oxidized to abscisic acid, of which it is probably the natural precursor and with which it shares the trans,trans configuration (Taylor and Burden, 1972). 

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). 

Blumenfeld A, Gazit S (1970) Interaction of kinetin and abscisic acid in the growth of soybean callus. Plant Physiol 45 535-536... 

Friedberg SH, Davidson D (1970) Duration of S phase and cell cycles in diploid and tetraploid cells of mixoploid meristems. Exp Cell Res 61 216-218 Fuchs Y, Lieberman M (1968) Effects of kinetin, lAA, and gibberellin on ethylene production, and their interactions in growth of seedlings. Plant Physiol 43 2029-2036 Gaither DH, Lutz DH, Forrence LE (1975) Abscisic acid stimulates elongation of excised pea root tips. Plant Physiol 55 948-949... 

Walker GWR, Dietrich J (1961) Kinetin-induced meiotic-prophase acceleration and stasis in Tradescantia anthers cultured on media deficient in sugar. Nature 192 889-890 Walton DC, Harrison MA, Cote P (1976) The effects of water stress on abscisic-acid levels and metabolism in roots of Phaseolus vulgaris L. and other plants. Planta 131 141-144... 

Cytokinins have also been reported to increase PA biosynthesis in some plant systems, while application of abscisic acid (ABA) leads to the contrary situation (see review in Smith, 1985a). For instance, benzyladenine increased putrescine and ADC activity in cucumber cotyledons. By contrast, ABA decreased putrescine and ADC activity (Suresh et ai, 1978 In rice seedlings, total PAs increased threefold after treatment with kinetin, but declined with ABA (Mukho-padhyay et ai, 1983). It has been proposed that the regulation of PA biosynthesis by ABA in the aleurone layers of barley seeds is exerted through inhibition of the conversion of putrescine to spermidine (Lin, 1985). 

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