METABOLIC PATHWAY FOR GLYCEROL SYNTHESIS UNDER OSMOTIC-STRESS IN THE FRESH-WATER GREEN-ALGA CHLAMYDOMONAS-REINHARDTII

The freshwater green alga Chlamydomonas reinhardtii accumulates and ex cretes glycerol in response to hyperosmotic shock. During the first ho urs, when photosynthetic activity is inhibited, the carbon source for the synthesis of glycerol is starch. Afterwards, when photosynthetic a ctivity recovers, the carbon source is CO2. Enzymes of the glycerol cy cle have been measured and different levels of activity have been foun d between control and salt-stressed cells. The differences finded (maj or activity for dihydroxyacetone phosphate phosphatase and minor activ ity for glycerol phosphate dehydrogenase in salt-stressed cells) do no t depend on protein synthesis, so the mechanism of regulation reside a t the level of enzyme activation. The signal that triggers this mechan ism and the identity of components that activate the enzymes are still not determined. A hypothesis for glycerol synthesis in C. reinhardtii is proposed.