ISOLATION AND STUDY OF MUTANTS LACKING A DEREPRESSIBLE PHOSPHATASE IN CHLAMYDOMONAS REINHARDI

R. F. Matagne ¹ and R. Loppes ¹

¹ Laboratory of Molecular Genetics, Department of Botany, University of Liège, Sart Tilman, B-4000 Liège, Belgium

In the green alga Chlamydomonas reinhardi, removal of inorganic phosphate from the culture medium results in the increase of phosphatase activity (derepression) in the wild-type (WT) strain as well as in a double mutant (P₂P_a) lacking the two main constitutive acid phosphatases. Following treatment of WT and P₂P_a with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), mutants were recovered which display very low phosphatase activities when grown in the absence of phosphate; as shown by electrophoresis, they lack one non-migrating phosphatase (PD mutants). This enzyme is active over a wide range of pH with an optimum at pH 7.5. The comparison of electropherograms from WT and mutants grown on media with or without phosphate allowed us to provide a tentative definition of the pool of derepressible phosphatases in Chlamydomonas : in addition to the neutral phosphatase lacking in PD mutants, Chlamydomonas produces two electrophoretic forms of alkaline phosphatase showing an optimal activity at pH 9.5.

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