Regulation of glycerol and starch metabolism in Chlamydomonas pulsatilla in response to changes in salinity

Abstract

Abstract. Chlamydomonas pulsatilla rapidly adjusts its level of osmoregulatory solute, glycerol, when exposed to increased (upshock) or decreased (downshock) salinities. Rates of degradation, or loss, of glycerol are similar in light and dark, while rates of net synthesis proceed about 20% faster in the light than in the dark. Synthesis of glycerol in the dark is correlated with degradation of starch, and starch appears also to be utilized for glycerol synthesis in response to extensive salinity upshocks in the light, where photosynthesis is strongly inhibited. Under conditions of moderate upshocks in the light, photosynthesis is not affected, and net increases in both glycerol and starch were observed. Glycerol turnover takes place both under iso‐osmotic conditions, and during period of adjustments to osmotic downshocks, where there is a rapid net decrease in the glycerol pool. Half times for glycerol turnover were estimated from rates of incorporation of photoassimilated 14C into glycerol and glycerol pool sizes to be 20 and 74 min for cells incubated at 50 and 100% artificial seawater, respectively.