Difluoromethylarginine (DFMA) and difluoromethylornithine (DFMO) are inhibitors of the polyamine biosynthetic enzymes arginine decarboxylase (ADC) and ornithine decarboxylese (ODC), respectively, DFMO is a potential fungicide acting on fungal ODC.

This report examines the effects of DFMA and DFMO on polyamine concentrations and metabolism, and on the activities of enzymes of polyamine biosynthesis and breakdown in the mycorrhizal fungus Laccaria proxima. Data indicate that L. proxima possesses both ADC and ODC activities: DFMA depleted putrescine and did not inhibit ODC activity; incubation of mycelium with a [U‐¹⁴C]arginine substrate led to [¹⁴C]putrescine formation DFMA completely inhibited the formation of polyamines from [U‐¹⁴C]arginine DFMO inhibited bound biosynthetic enzyme activity and the formation of putrescine from [U‐¹⁴C]ornithine. Therefore, L. proxima may not be susceptible to fungicidal DFMO application.