O-HYDROXYPHENYLACETIC ACID-ENHANCED RICE COLEOPTILE ELONGATION

o-Hydroxyphenylacetic acid (o-HPAA), a phytotoxin from decomposed rice residues, could enhance the elongation of rice (Oryza saliva L.) coleoptiles. Its isomers, p-HPAA, a naturally occurring auxin, and m-HPAA however had little effect. The o-HPAA-enhanced coleoptile elongation was observed in rice rather than other cereal crops (barley, wheat, oat, and corn). Levels of free putrescine increased in o-HPAA-treated coleoptiles. An inhibition of the o-HPAA-induced putrescine increase by alpha-difluoromethylarginine (DFMA), an irreversible inhibitor of arginine decarboxylase (ADC; E.C. 4.1.1.19), rather than alpha-difluoromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase (ODC; E.C. 4.1.1.17), indicates that ADC is involved in this putrescine accumulation. The o-HPAA-enhanced elongation of coleoptiles was inhibited by DFMA but the application of putrescine can not reverse DFMA's effects. The ethylene biosynthesis inhibitor, Co2+, at 0.1 mM, did not affect the o-HPAA-enhanced coleoptile elongation. The ethylene production rate in o-HPAA-treated rice seedlings was also the same as the controls. It seems ethylene does not play a role in the o-HPAA-enhanced elongation of rice coleoptiles.