Effects of light on phospholipid metabolism in DunaUella salina

Dunalliella salina (Teodoresco) is a unicellular, wall-less, halotolerant green alga. Previous work has shown that levels of inositol phospholipiils in whole cells of D. salina fluctuate in response to hyper- and hypo-osmotic shock. In this paper, we report the effects of changes in the light environment on levels of phospholipids, including inositol phospholipids, in D. scilina. Utilizing both short-term and long-term labeling of phospholipids with ³²PO₄, we were able to compare both immediate and long-term changes in lipid metabolism during changes in the light environment. Relative to the other phospholipids. phosphotidic acid and the inositol phospholipids phosphatidylinositol, phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate were rapidly labeled, even in the dark, suggesting that the metabolism of these compounds is more active than that of the bulk cellular phospholipids. There was little change in inositol phospholipid metabolism when cells were illuminated following a 1 h dark adaptation period, Furthermore, the inositol phospholipid signal transduction pathway did not respond to severe photoinhibition treatment. Apparently this plasma-membrane-based signal transduction pathway, which responds to changes in the external environment, is relatively insensitive to major changes in chloroplast metabolism.