The role of vanadium in gree plants. II. Vanadium in green algae--two sites of action.

Cells of Chlorella pyrenoidosa, derived from vanadium free agar slants, respond with great sensitivity to microamounts of vanadium, added as NH4VO3 to autotrophic liquid cultures. Between 0.01 and 1 microgram V per litre nutrient medium (2-10(-10)-2-10(-8) g-at/1), the algae respond with a continuous incrase in dry weight. At higher V-concentrations, further enhancement in biomass is accompanied by a additional increase in chlorophyll content. Maximum V-effect on both parameters was found to be at 500 microgram V/1 (10(-5) G-AT/1). Dry weight as well as chlorophyll content of Chlorella are decreased by concentrations above 25 mg V/1; 100 mg V/1 (2-10(-3) g-at/1) stop growth and cause death of the cells. The toxic threshold for the V-content in the algae was determined to be at 150-200 microgram V/g (3-4-10(-6) g-at/g) dry weight. Two different pH-optima for a positive vanadium action on dry weight and chlorophyll biosynthesis were established, the first at pH 7, the other in the range pH 7.5--8. Two sites of vanadium action in green algae are discussed.