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.