POLYAMINE METABOLISM DURING SEEDLING DEVELOPMENT IN RICE

The main free amines identified during growth and development of rice seedlings were agmatine, putrescine, spermidine, diaminopropane and ty ramine. Amine composition differed according to tissue and stages of d evelopment. Conjugated amines were only found in roots. We present evi dence that arginine decarboxylase (ADC) regulates putrescine during th e development of rice seedlings. When ADC action was blocked by DFMA ( alpha-DL-difluoromethylarginine, a specific irreversible inhibitor of ADC), polyamine titers and seedling development were diminished; when agmatine or putrescine was added, normal polyamine titers and growth w ere restored. The effects of DFMA were concentration dependent. DFMO ( alpha-DL-difluoromethylornithine, a specific irreversible inhibitor of ornithine decarboxylase or ODC) promoted growth and development at co ncentrations below 2 mM. This effect was probably related to its unexp lained, but consistently observed slight enhancement of rice ADC. When the increase in the concentration of spermidine was prevented by CHA (cyclohexylammonium sulfate), the number of roots increased and the in crease in length of leaves and roots was strongly inhibited. The addit ion of exogenous spermidine at the time of treatment with CHA reversed the inhibition by CHA.