Cytokinin Relations in the Whole Plant
Cytokinin levels in Xanthium strumarium decline rapidly throughout the plant after only one short-day cycle. This effect appears to be due to reduced cytokinin production by the roots, in response to a signal produced in the leaves during long dark periods.
Disbudding of seedlings of Phaseolus vulgaris leads to the accumulation of high levels of dihydrozeatin-O-β-D glucoside in the leaves, where it appears to be formed from an intermediate supplied from the roots. In short-term experiments 8-14C zeatin is rapidly converted in the leaves to zeatin-O-β-D glucoside, which is later degraded to adenine and related compounds. It is suggested that dihydrozeatin-O-β-D glucoside accumulates in the leaves of disbudded plants because it is resistant to “cytokinin-oxidase” type enzymes. In roots and buds of P. vulgaris, zeatin is converted to zeatin ribotide rather than to glucosides. Cytokinin interrelations in the whole plant are discussed in relation to biosynthesis, transport, and metabolism.
KeywordsRoot Exudate Dark Period Intact Plant Endogenous Cytokinin Zeatin Riboside
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