CONCOMITANT CHANGES IN PHOSPHATE-UPTAKE AND PHOTOPHOSPHORYLATION IN THE BLUE-GREEN-ALGA ANACYSTIS-NIDULANS DURING ADAPTATION TO PHOSPHATE DEFICIENCY

The activation of the phosphate incorporation system of the blue-green alga Anacystis nidulans during phosphate deficiency was investigated. The adaptation to low external phosphate concentrations affects both the process of phosphate transport into the cell and the subsequent photophosphorylation in the following ways: The activated transport system becomes sensitized to vanadate, indicating the involvement of a plasma membrane ATPase under these conditions, and phosphate deficiency results in changes of the kinetic and energetic properties of the ATP synthase of the thylakoid membrane. Using broken spheroplasts that contained active thylakoids capable of performing cyclic photophosphorylation with PMS it was found that the apparent K(M) for phosphate at 1 mM ADP decreased from levels of about 260-mu-M for algae originating from batch culture with millimolar phosphate to 30-40-mu-M for algae kept under phosphate limited culture conditions. This change in the kinetic properties was accompanied by an alteration of the H+/ATP stoichiometry from about 3 for batch algae to 4 for phosphate deficient algae. The effect of these changes on the equilibrium phosphate concentration in the cytoplasm is discussed.