Changes in endogenous levels of free polyamines during petiole elongation in the semiaquatic plant Ranunculus sceleratus

We investigated the relationships between polyamines and indole-3-acetic acid- (IAA) and ethylene-induced petiole elongation in Ranunculus sceleratus. When applied exogenously, polyamines inhibited IAA-induced petiole elongation in the presence or absence of ethylene. An inhibitor of arginine decarboxylase, -difluoromethylarginine, stimulated IAA-induced petiole growth. IAA, ethylene, and fusicoccin all caused decreases in levels of endogenous spermine and other polyamine(s) (spermidine or putrescine or both). According to our kinetic studies, IAA and ethylene induced changes in endogenous polyamine contents at late stages of petiole elongation. Based on these results, we conclude that polyamines are involved in the regulation of IAA- and ethylene-induced growth, especially in late stages of petiole elongation in Ranunculus.