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  • Title: Cytokinin metabolism in Narcissus bulbs: chilling promotes acetylation of zeatin riboside.
    Author: Letham DS, Smith NG, Willcocks DA.
    Journal: Funct Plant Biol; 2003 Jul; 30(5):525-532. PubMed ID: 32689037.
    Abstract:
    The levels of the cytokinins zeatin, dihydrozeatin and N6-(isopent-2-enyl)adenine and the corresponding 9-ribosides were determined in whole Narcissus pseudonarcissus L. bulbs after onset of summer dormancy, and after storage of the dormant bulbs at 4 or 15°C under moist conditions. The cytokinin level was increased at both temperatures; the dominant cytokinin at 15°C was zeatin riboside but at 4°C the free base, zeatin, was the principal cytokinin. The metabolism of 3H-labelled zeatin, zeatin riboside and 6-benzylaminopurine was studied in scales and base plates excised from bulbs previously held at 4 or 15°C. The chilling treatment promoted conversion of [3H]zeatin riboside to O-acetylzeatin riboside (an unusual cytokinin metabolite) in the excised base plate and inhibited 9-riboside formation from 6-benzylaminopurine. Chilling also promoted formation of O-acetylzeatin riboside from [3H]zeatin in excised scale tissue. Endogenous O-acetylzeatin and O-acetylzeatin riboside were concentrated in the base plate. Relative to zeatin riboside, O-acetylzeatin riboside was degraded to adenosine and related compounds less rapidly in the leaf cluster. Since acetylation of the zeatin side chain enhances activity in cytokinin bioassays, O-acetylzeatin riboside may play a role in leaf development following chilling of Narcissus bulbs.
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