Gibberellic acid cytokinin

Terpenoids, which are also known as isoprenoids, constitute the most abundant and structurally diverse group of plant secondary metabolites, consisting of more than 40,000 different chemical structures. The isoprenoid biosynthetic pathway generates both primary and secondary metabolites that are of great importance to plant growth and survival. Among the primary metabolites produced by this pathway are phytohormones, such as gibberellic acid (GA), abscisic acid (ABA), and cytokinins the carotenoids, such as chlorophylls and plastoquinones involved in photosynthesis the ubiquinones required for respiration and the sterols that influence membrane stmcture (see also Steroid and Triterpene Biosynthesis) (Fig. 1). Monoterpenoids (CIO), sesquiterpenoids (Cl5), diterpenoids (C20), and... 

In order to improve yields and productivities of secondary metabolites in plant cell culture s it is essential the selection of the most elEcient plant growth regulators (auxins, cytokinins, gibberellic acid and abscicic acid) and the relationship between diem [74, 75]. 

Beyond these various defense compoimds, plants synthesize a wide variety of signaling molecules (oxylipins, brassinosteroids, gibberel-lins, cytokinins, strictolactones) [25], pigments (chlorophylls, carotenoids) [26], and fatty acids and sterols [27]. In the perspective of this chapter, it is worth noting that the production of many of these plant compoimds depends on both chlo-roplast enzymes, which include a small number of soluble P450s, and endoplasmic reticulum enzymes, which include the bulk of membrane-bound P450s. 

Malik CP, Mehan M (1975 b) Interaction between cycocel and gibberellic-acid in pollen-tube elongation of Calotropis procera. Curr Sci 44 785-786 Manos GE (1961) The effects of growth substances on attached and detached root tips of Pisum sativum L. Physiol Plant 14 697-711 Manos PJ, Goldthwaite J (1976) An improved cytokinin bioassay using cultured soybean hypocotyl sections. Plant Physiol 57 894-897 Marinos NG (1960) Some responses of Avena coleoptiles to ethylene. J Exp Bot 11 227-235... 

Application of zeatin in agar gels to the apical ends of stem segments before sectioning them produced some increase of the auxin efflux. The most interesting action of both cytokinin and gibberellic acid, however, was prevention of the depressive effect of abscisic acid upon the wave-like pattern of the basipetal efflux of auxin (Fig. 7.2 C, D). 

A delay of senescence can also be produced in some cases with lAA, synthetic growth substances and gibberellic acid. However, the effect of these other phytohormones is much less pronounced. With the cytokinins the effect is, on the contrary, so striking that a few assay procedures for cytokinins are based on it. 

Figure 1. Effects of CaCl2 on bioassays for auxin, gibberellin, and cytokinin. A effects of CaCl2 on elongation of oat coleoptile sections in the presence and absence of indoleactic acid B effects on elongation of lettuce hypocotyls in the presence and absence of gibberellic add and C effects on enlargement of Xanthium cotyledon pieces in the presence and absence of benzyladenine (13).

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