The effectiveness of inhibitors of polyamine biosynthesis in controlling
plant pathogenic fungi is well established. The spermidine synthase
inhibitor cyclohexylamine (CHA) and the spermidine analogue norspermidine
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 growth
by 63%. Neither inhibitor had any effect on ODC or AdoMetDC activities,
nor the flux of label from ornithine through to the polyamines. Levels of free
polyamines in fungal tissue exposed to 0.01 mM norspermidine were unaltered,
although 1.0mM CHA did produce a 75% increase in fungal putrescine
content. These data suggest that CHA and norspermidine do not reduce
fungal growth as a result of a perturbation in polyamine biosynthesis.