Dicyclohexylamine-Induced Shift of Biosynthesis from Spermidine to Spermine in Plant Protoplasts

An improved analytical method, based on high pressure liquid chromatography, has been developed for the simultaneous determination of the polyamines and S -adenosyl-containing compounds in extracts of plant protoplasts. The method involves simple procedures for sample preparation and permits quantification of 1 picomole or less for all the compounds. This method has been used to study the effects of dicyclohexylamine, an inhibitor of plant spermidine synthase (Sindhu, R. K., S. S. Cohen 1984 Plant Physiol 74: 645-649), on biosynthesis of polyamines and 1-aminocyclopropane-1-carboxylate in protoplasts derived from Chinese cabbage leaves. Dicyclohexylamine effectively inhibits spermidine synthase in vivo. Inhibition of the synthesis of spermidine by dicyclohexylamine resulted in a stimulation of spermine synthesis, without significant effect on the synthesis of 1-aminocyclopropane-1-carboxylate. Decarboxylated S -adenosylmethionine is present in control Chinese cabbage protoplasts at ∼10 −18 moles per cell, and dicyclohexylamine caused an increase of this metabolite of up to 10-fold in a 4-hour period. The increase in decarboxylated S -adenosylmethionine permitted an increased synthesis of spermine. These findings suggest that the availability of decarboxylated S -adenosylmethionine may be rate-limiting for the synthesis of spermine in plant protoplasts.