Transport and Metabolism of Dihydrozeatin Riboside in Germinating Lupin Seeds

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Abstract
[3H]-dihydrozeatin riboside was applied selectively to the embryonic axes or to the cotyledons of germinating lupin (Lupinus luteus L. cv. Weiko III) seeds 6 h following the start of imbibition. There was little transport of dihydrozeatin riboside from embryo to cotyledons up to 6 h after the application, but a substantial amount of radioactivity had moved into the cotyledons at the end of the 10 h incubation period. However, there was no detectable movement of [3H]-dihydrozeatin riboside from the cotyledons to the embryonic axis. This indicated a highly polarized movement of cytokinins during the early stages of seed germination. Exogenously applied [3H]-dihydrozeatin riboside was found to be very stable, both when applied to the embryonic axes and cotyledons of intact seed, or following excision, and there was little metabolism with only small amounts of radioactivity found associated with degradative metabolites. The embryonic axis of this species has recently been found to synthesize cytokinins within 12 h from the start of imbibition, and the results of this study indicate that the embryo-derived cytokinin is probably transported to the cotyledons where it accumulates and subsequently participates in the control of cotyledon function.