Abstract
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 (α- 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 (α- 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.
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