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Types, Formation, and Metabolism of Cytokinins in Leaves of Alnus glutinosa (L.) Gaertn

I. E. HENSON
Journal of Experimental Botany
Vol. 29, No. 111 (August 1978), pp. 935-951
Published by: Oxford University Press
Stable URL: http://www.jstor.org/stable/23689513
Page Count: 17
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Types, Formation, and Metabolism of Cytokinins in Leaves of Alnus glutinosa (L.) Gaertn
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Abstract

The nature of the cytokinins present in mature, expanded leaves of alder (Alnus glutinosa (L.) Gaertn.) was investigated using a chromatographic system capable of partially resolving zeatin from (±)-dihydrozeatin. A zeatin-like cytokinin, present as both a 'free' form and as a polar conjugate, postulated to the the O-β-D-glucoside of zeatin, accounted for the bulk of the cytokinin activity (detected by the soybean callus assay). Studies on the fate of [8-14C]zeatin supplied to detached alder leaves indicated this cytokinin to undergo extensive metabolism. An appreciable proportion of the radioactivity was incorporated into 80% methanol-insoluble and soluble acidic/neutral fractions, while adenosine- and adenine-like peaks were prominent metabolites in the basic n-butanol-soluble fraction. Small amounts of glucosides, with the properties of both zeatin-O-β-D-glucoside and dihydrozeatin-O-β-D-glucoside were formed, the latter becoming the most prominent with time. The ability of alder leaves to form glucoside directly from (±)-dihydrozeatin was assessed using the soybean callus assay. (±)-Dihydrozeatin was subject to a relatively rapid, continuous and substantial conversion to its putative O-β-D-glucoside and cytokinin activity was consequently conserved while, in contrast, leaves supplied with zeatin exhibited a progressive loss of cytokinin activity and, in agreement with the radioactivity experiments, produced only a small amount of activity attributable to the putative O-glucosides. The significance of the observed cytokinin metabolism is discussed in relation to the endogenous cytokinin status of the leaf.

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