Activités phosphatases et carence phosphatée chez des champignons supérieurs

Abstract

Six mycorrhizal and three saprophytic fungi were collected. They were cultivated in a liquid medium with or without a deficiency in phosphate. Different phosphatase activities were measured from the mycelia: phosphatase activities accessible to an external substrate, phosphatase activities in the culture medium, phosphatase activities of the whole homogenate and two parts of this homogenate (parietal and soluble). With both the mycorrhizal and saprophytic fungi, the deficiency in inorganic phosphate induced a large increase in phosphatase activities which were multiplied on the average by a factor of 72, 56, 43, 64, and 26, for the excreted, accessible, total, parietal, and soluble activities, respectively. If the relative proportions of the various activities were considered, the parietal activity, compared with the total phosphatase activity, increased in six out of nine cases under the effect of phosphate deficiency. The superiority of the parietal activity over the soluble activity was either induced by phosphate deficiency or preexisting. The accessible activity represented only a fraction of the parietal activity and this was usually smaller in a phosphate-deprived medium. Various criteria have been considered to class these fungi in terms of their response to phosphate deficiency, such as the intensity of their phosphatase response to the deficiency and the absolute values in a phosphate-deprived medium of various phosphatase activities. These various criteria do not lead to a classification entirely parallel of the different fungi and they do not discriminate between mycorrhizal and saprophytic fungi.