INHIBITION OF POLYAMINE BIOSYNTHESIS IN PHYTOPHTHORA-INFESTANS AND PYTHIUM-ULTIMUM

Mycelial growth, polyamine concentrations and the activities of enzymes of polyamine biosynthesis and catabolism were examined in Phytophthora infestans and Pythium ultimum grown in the presence of difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase (ODC), and difluoromethylarginine (DFMA), an inhibitor of arginine decarboxylase (ADC). Growth of P. infestans was reduced by DFMO and a mixture of DFMO + DFMA, but was increased by DFMA at concentrations of 5 mM and greater. Polyamine concentrations and ODC activity were significantly reduced in P. infestans grown on all inhibitor treatments. In contrast, growth, polyamine concentrations and enzyme activities were not affected in P. ultimum exposed to the inhibitors. It seems unlikely that P. infestans and P. ultimum possess ADC activity, as neither of the products of ADC activity (agmatine and putrescine) could be detected in ADC assays. Although ODC from P. infestans was sensitive to DFMO, ODC from P. ultimum was insensitive to the inhibitor. Moreover, uptake of DFMO by P. infestans was three times greater than that observed by P. ultimum.