INSENSITIVITY OF SEPTORIA-TRITICI AND USTILAGO-MAYDIS TO INHIBITORS OF ORNITHINE DECARBOXYLASE

Growth of Septoria tritici and Ustilago maydis is relatively insensitive to 1 mm difluoromethylornithine (DFMO), and other potent enzyme-activated inhibitors of ornithine decarboxylase (ODC). For the ODC from S. tritici, the K(i)s for DFMO, dehydromonofluoromethylornithine (DELTA-FMO) and methylacetylenicputrescine (MAP) are 22, 5, and 35-mu-M respectively, and the ODC from U. maydis appears to be similarly sensitive. On growing in 1 mm-DFMO, the polyamine content, which consisted mainly of spermidine in both fungi, is reduced to 30-40%. DFMO appears to penetrate freely into both fungi. The maximum ornithine concentration is about 12 mm in S. tritici and about 0.6 mM in U. maydis when grown in DFMO. In S. tritici neither arginine, citrulline nor acetylornithine appeared to serve as precursors for putrescine, and growth was not inhibited by 1 mm difluoromethylarginine (DFMA), or -citrulline (DFMC). In U maydis no evidence was found for the decarboxylation of arginine or citrulline.