Regulators of cell division in plant tissues. XXX. Cytokinin metabolism in relation to radish cotyledon expansion and senescence

Abstract

Abstract. Kinetic studies of formation of glucosides of 6-benzylaminopurine (BAP) in excised radish cotyledons indicated that the 3-, 7-, and 9-glucosides (N-glucosides) were each formed directly from BAP. The 7-and 9-glucosides of BAP and the 7-glucoside of zeatin exhibited great stability in the cotyledons, but the 3-glucoside was converted to free BAP and to the 7-and 9-glucosides of BAP. When 3H-labeled zeatin was supplied to developed cotyledons, at high concentrations (100 I~M), 7-glucosylzeatin was the principal metabolite, but an appreciable proportion of the extracted 3H was due to O-glucosylzeatin. In immature cotyledons, as used in the radish cotyledon cytokinin bioassay, this O-glucoside was shown to be converted into zeatin 7-glucoside probably via free zeatin.Metabolism of BAP and zeatin in radish cotyledons was studied in relation to cytokinin-induced cotyledon expansion. Cytokinin N-glucosides were not metabolites responsible for the observed cytokinin-induced expansion, and were not detoxification products, or deactivation products formation of which was coupled with cytokinin action. However, the free base, its riboside, and nucleotide were possible active forms of BAP associated with cotyledon expansion. The possible significance of cytokinin N-glucosides is discussed.Senescent and nonsenescent cotyledons differed in their metabolism of BAP, zeatin, and zeatin riboside. Senescence was associated principally with a reduction in ability to form 7-glucosylzeatin, enhanced metabolism to adenine derivatives, and an inability to form appreciable amounts of 3-glucosyl-BAP.A two-dimensional thin layer chromatography (TLC) system, based on adjoining layers of cellulose and silica gel, for separating zeatin metabolites

Inhibitors of cytokinin metabolism III. The inhibition of cytokininN-glucosylation in radish cotyledons

“…This is in accord with previous studies. Indeed it was found that a 90% reduction in 3H-labeled cytokinin uptake by radish cotyledons did not appreciably change the percentage of radioactivity present as N-glucosides (Letham and Gollnow 1985). Hence, the inhibitorinduced reductions in cytokinin uptake do not affect the validity of the data presented in Tables 1 and 2.…”

“…The presence of (OG)Z was confirmed by 13-glucosidase hydrolysis and rechromatography. When the cotyledon extracts were subjected to chromatography using a bilayer 2D TLC system (Letham and Gollnow 1985), the percentages of radioactivity found for the various metabolites were similar to those determined by the procedure outlined above. Eluates of the 2D TLC Z and [9R]Z spots, derived from extracts of cotyledons supplied with [3H][9R]Z in the presence of some inhibitors, were rechromatographed using TLC systems (Parker et al 1978) which separate Z from dihydrozeatin (DZ) and [9R]Z from dihydrozeatin riboside [9R]DZ.…”

“…In excised radish cotyledons, 6-benzylaminopurine (BAP) is N-glucosylated to give the 3-, 7-, and 9-glucosides, termed [3G]BAP, [7G]BAP, and [9G]BAP, respectively. In this tissue [3G]BAP may be converted back to BAP, so it cannot be considered a deactivation product (Letham and Gollnow 1985). Zeatin (Z) and zeatin derived from exogenous zeatin riboside ([9R]Z) yields only one N-glucoside in appreciable amounts, 7-glucopyranosytzeatin ([7G]Z).…”

Cytokinin biochemistry in relation to leaf senescence. III. The senescence-retarding activity and metabolism of 9-substituted 6-benzylaminopurines in soybean leaves

“…For reversed phase TLC, layers spread with Merck silica gel 60 GF254 were impregnated with dimethylpolysiloxane-5X (Letham and Gollnow 1985) and are termed DMPS layers henceforth . The following solvents were used (proportions are by volume) : A, 1-butanol-water-14 N ammonia (6 :2 :1, upper phase) ; B, methanol-water (1 :1); C, chloroform-methanol (9 :1); D, methanol-water (2 :3) ; E, propyl acetate-acetic acid-water (20 :9 :5); F, 1-butanol saturated with water .…”

Control of axillary bud initiation and shoot architecture in Arabidopsis through the SUPERSHOOT gene

“…Cytokinin bases (Z, DZ, and iP) and Z-9-glucoside were measured directly, but the O-glucosides were first hydrolyzed to bases with ␤-glucosidase (Yong et al 2000). Z-7-glucoside was converted to Z by periodate oxidation and cleavage with freshly distilled cyclohexyl-amine (Letham and Gollnow 1985) before immunoassay.…”