Effect of polyamines and polyamine biosynthesis inhibitors on spore germination and hyphal growth of Glomus mosseae

The main free polyamines identified in ungerminated spores of Glomus mosseae were putrescine and spermidine. Changes in the level of these metabolites occurred during dormancy break induced by a cold treatment. Exogenous application of these polyamines to spores after a dormancy break led to a marked increase in hyphal growth, suggesting that endogenous concentrations of putrescine and spermidine could be growth limiting factors. When polyamine biosynthesis via ornithine decarboxylase (ODC) was blocked by DFMO (alpha-DL-difluoromethylornithine), a specific irreversible inhibitor of ODC, spore germination and hyphal growth were greatly reduced. These effects were DFMO concentration-dependent. Simultaneous treatment with DFMO and putrescine attenuated the inhibitory effect of DFMO on hyphal growth indicating that polyamines may be involved in regulating hyphal growth of G. mosseae. In contrast, DFMA (alpha-DL-difluoromethylarginine), a specific irreversible inhibitor of arginine decarboxylase (ADC), the other pathway for polyamine biosynthesis, promoted hyphal growth. These results suggest that in G. mosseae, polyamine biosynthesis during hyphal growth is regulated by ODC. Both DFMO and DFMA have been shown to provide control of a number of plant diseases caused by phytopathogenic fungi, but only the use of the latter appears compatible with the development of a symbiotic endomycorrhizal fungus.