Mechanism of cytokinin action on auxin-induced ethylene production

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The stimulative effect of cytokinin on ethylene production has been examined in etiolated mungbean hypocotyl segments. The rate of auxin-induced production linearly increased with time in a certain range of exogenous IAA concentration. The rate of induced production doubled with a 10-fold increase in exogenous IAA concentration or addition of benzyladenine at 5 μM. Benzyladenine did not suppress inactivation of the induced ethylene producing system. Although the free IAA level within the tissues was slightly increased by benzyladenine accompanied by a decrease in IAASp formation, the increased free IAA level did not account for the doubling of the production rate. When the tissues were preincubated with benzyladenine alone followed by postincubation with auxin, the rate of induced production in pretreated tissues was significantly higher than that in untreated or buffer-treated tissues supplied with auxin and benzyladenine simultaneously in the post-incubation medium. Formation and disappearance of the cytokinin effect were temperature dependent. The rate of endogenous production was constant over an experimental period and benzyladenine simply enhanced the rate several-fold after a lag period. Kinetics of the cytokinin stimulation was not the inductive type. Based on these observations, a possible mechanism of the stimulative effect of cytokinin was discussed.
日本植物生理学会の論文