INHIBITION OF ROOT-GROWTH BY SPERMIDINE IS NOT DUE TO ENHANCED PRODUCTION OF ETHYLENE

Pretreatment of 3-day-old maize seedlings with spermidine induces an e nhancement of ethylene production from roots compared to control tissu es with no effect on 1-aminocyclopropane-1-carboxylate oxidase activit y and 1-aminocyclopropane-1-carboxylic acid level, accompanied by a st rong inhibition of root growth. Inhibitors of ethylene synthesis, coba lt chloride and amindethoxy-vinylglycine, markedly inhibited ethylene production in both control and spermidine-pretreated roots. The decrea se in ethylene production did not result in reversing the inhibition o f root growth induced by spermidine, Results suggest that the stimulat ion of ethylene by spermidine, probably due to more available S-adenos ylmethionine, is not responsible for the inhibitory effect of spermidi ne on root growth. This statement is substantiated by the ineffectiven ess of silver thiosulfate, a known inhibitor of ethylene action, to re move spermidine-mediated inhibition of root growth.