Proteinase activity in mycorrhizal fungi III.

summary A study was made of the potential of low molecular weight sources of nitrogen (N) and carbon (C), of the kind that can occur in the rhizosphere of ericoid roots, to influence the production of extracellular acid proteinase by Hymenoscyphus ericae (Read) Korf & Kernan. The fungus was grown in liquid culture with either pure protein or with protein hydrolysate as sole source of N and C and the effect of supplementation with ammonium and glucose was investigated. Proteinase production was induced as effectively by protein hydrolysate as by pure protein but in each case was enhanced in the presence of a low concentration (10 μg ml−1) of ammonium. Maximum enzyme production was found in those cultures that were supplied with protein or hydrolysate as sole sources of carbon, a feature which was associated with release of additional ammonium. This ammonification coincided with an increase of pH to a final value of 645, at which point the enzyme appeared to be inactivated. Glucose strongly repressed proteinase production when the endophyte was grown with protein, but not when grown with hydrolysate. These contrasting responses suggest that conditions leading to induction exert a stronger influence over enzyme production than do conditions leading to repression. In addition, hydrolysis products of protein must be present before full enzyme production is induced. The interacting effects of C and organic or inorganic N on proteinase production by the mycorrhizal fungus are discussed in relation to conditions prevailing in heathland soil.