LOW-LEVEL OF INORGANIC ORTHOPHOSPHATE IN GROWTH-MEDIUM INCREASES METABOLISM AND EXCRETION OF GLYCOLATE BY CHLORELLA-VULGARIS CELLS CULTIVATED UNDER AIR CONDITIONS

Cells of the green alga Chlorella vulgaris Beijer were cultivated in n on-synchronized cultures under atmospheric levels of O-2 and CO2 in co mplete (control) or phosphorus-deficient inorganic medium. The growth of the cells, their content of soluble organic and inorganic phosphoru s, photosynthetic and respiratory oxygen exchange, and glycolate conce ntration in the medium were assayed. Suspensions of cells from control and phosphorus-deficient cultures were prepared in fresh medium, glyc olate-free or containing exogenous glycolate, and the rate of glycolat e excretion under light and of glycolate uptake and metabolism in the dark were also analysed. Phosphorus deficiency resulted in lowering of phosphate content in cells, more pronounced organic than inorganic co mpounds, and increased glycolate level in the growth medium. It enchan ced the excretion and metabolism of glycolate by the cells. The result s are discussed in relation to the role of the photorespiratory carbon oxidation cycle (photorespiration) in photosynthetic recycling of pho sphorus and in regulation of inorganic orthophosphate concentration wi thin the chloroplasts.