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 ac id- (IAA) and ethylene-induced petiole elongation in Ranunculus sceleratus. When applied exogenously, polyamines inhibited IAA-induced petiole elongat ion in the presence or absence of ethylene. An inhibitor of arginine decarb oxylase, a-difluoromethylarginine, stimulated IAA-induced petiole growth. I AA, ethylene, and fusicoccin all caused decreases in levels of endogenous s permine and other polyamine(s) (spermidine or putrescine or both). Accordin g to our kinetic studies, IAA and ethylene induced changes in endogenous po lyamine contents at late stages of petiole elongation. Based on these resul ts, we conclude that polyamines are involved in the regulation of IAA- and ethylene-induced growth, especially in late stages of petiole elongation in Ranunculus.