The effects of polyamine biosynthesis inhibitors on mycelial growth, enzyme activity and polyamine levels in the oat-infecting fungus Pyrenophora avenae

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Abstract
The fungus Pyrenophora avenae, an important pathogen of oat crops, was grown on solid and liquid media containing the polyamine biosynthesis inhibitors difluoromethylornithine (DFMO), methylglyoxal bis(guanylhydrazone) (MGBG), ethylmethylglyoxal bis(guanylhydrazone) (EMGBG +/- polyamines. All of the compounds inhibited mycelial growth of the fungus. MGBG and EMGBG were more effective than DFMO. The addition of putrescine and spermidine almost completely prevented inhibition of mycelial growth by DFMO. However, no such effect was observed for inhibition by MGBG or EMGBG. Neither the inhibitors nor exogenous polyamines had any significant effect on the size of the fungal cells. DFMO and MGBG, alone and in combination, reduced the activity of ornithine decarboxylase. Fungus grown in media containing EMGBG showed reduced activity of S-adenosylmethionine decarboxylase. Putrescine and spermidine concentrations decreased when the fungus was grown in media containing DFMO or DFMO/MGBG combined. MGBG reduced spermidine and spermine concentrations and EMGBG greatly reduced spermidine concentrations. All of the compounds reduced the concentration of cadaverine, which is a significant component of P. avenae. The respiration rate of the fungus decreased when grown in media containing MGBG or DFMO/MGBG combined.