Several inhibitors of polyamine biosynthesis reduced mycelial growth of the fungus Ophiostoma ulmi (Buism.) Nannf. cultured on malt extract-agar medium. Growth inhibition was particularly evident when expressed in terms of fresh weight rather than colony diameter. Of the different drugs tested, the most effective was difluoromethylarginine (DFMA), while difluoromethylornithine (DFMO) and methylglyoxal(bis)guanyl-hydrazone (MGBG) plus cyclohexylamine (CHA) reduced growth only by 75 and 62% respectively. The growth inhibition by DFMO + DFMA, measured as colony diameter, was apparently reversed by putrescine (PUT), but not when expressed in terms of fresh weight. Spermidine (SPD) was the most abundant polyamine in control cultures, followed by PUT and spermine (SPM). PUT was no longer detectable 8 d after inoculation. On day 10, DFMO and DFMA, alone and in combination, caused a significant reduction in cellular SPD concentrations, while exogenously supplied PUT restored the levels of this polyamine to control values. MGBG + CHA caused a conspicuous accumulation of PUT and an approximately 50% reduction in SPD titres. DFMA, alone or in combination with DFMO and with or without PUT, led to increased cellular levels of SPM. The latter polyamine, but not PUT or SPD, strongly retarded growth when added to the growth medium. As suggested by the effectiveness of DFMA in inhibiting growth, arginine decarboxylase activity was shown to be prevalent over ornithine decarboxylase activity in this fungus.
Keywords: Ophiostoma ulmi; arginine decarboxylase; ornithine decarboxylase; polyamine biosynthesis inhibitors; polyamines.