Inhibition of Cytokinin Action and of Heat/Aging Induced Potential for Cytokinin Action by Inhibitors of Membrane Synthesis and Function

Abstract

Evidently, cytokinin action, in inducing the biosynthetic pathway involved in betacyanin synthesis in Amaranthus tricolor seedlings, is dependent on membrane synthesis and function. The experimental system included a pretreatment of heat shock (40.degree. C) and aging of cotyledon explants. This produced the conditions necessary for the full expression of cytokinin potential during the subsequent betacyanin induction. Cerulenin, an inhibitor of fatty acid and sterol synthesis, inhibited the heat-induced potential for cytokinin action and the benzyladenine-dependent induction itself. This was true of metyrapone, an inhibitor of hydroxylation reactions involving cytochrome P450. Gammexane, an inhibitor of phospholipid turnover, impaired the heat-induced process but not the benzyladenine-dependent betacyanin accumulation. This was the case with 2-isopropyl-4-dimethylamino-5-methyl phenyl-1-piperidine carboxylate methyl chloride, an inhibitor of the cyclization steps in sterol and gibberellin synthesis. Filipin at 100 .mu.g/ml inhibited both processes, particularly the heat-induced potential. The effect of various steroids and fatty acids on induction is recorded together with experiments aimed at using them to reverse some of the inhibitions. The effects of cerulenin on heat-induced potential was partially reversed by preparations of Amaranthus lipids. Some reversal of the filipin effects was obtained with .beta.-sitosterol and stigmasterol. Evidently, membrane synthesis is stimulated during the heat/aging pretreatment and during the induction and some membrane function(s) is necessary for subsequent cytokinin action.