GROWTH AND POLYAMINE METABOLISM IN PYRENOPHORA-AVENAE EXPOSED TO CYCLOHEXYLAMINE AND NORSPERMIDINE

The effectiveness of inhibitors of polyamine biosynthesis in controlli ng plant pathogenic fungi is well established. The spermidine synthase inhibitor cyclohexylamine (CHA) and the spermidine analogue norspermi dine were evaluated against in vitro growth of the oat stripe pathogen Pyrenophora avenae. Mycelial growth was reduced by 55% upon exposure to 2.0 mM CHA while the same concentration of norspermidine reduced gr owth by 63%. Neither inhibitor had any effect on ODC or AdoMetDC activ ities, nor the flux of label from ornithine through to the polyamines. Levels of free polyamines in fungal tissue exposed to 0.01 mM norsper midine were unaltered, although 1.0 mM CHA did produce a 75% increase in fungal putrescine content. These data suggest that CHA and norsperm idine do not reduce fungal growth as a result of a perturbation in pol yamine biosynthesis.