Abstract
We previously reported that a green alga, Chlamydomonas reinhardtii, induces degradation of sulfoquinovosyl diacylglycerol (SQDG), an acidic sulfolipid in chloroplasts, on sulfur (S)-starvation for yielding an intracellular S-source. We report here that, in contrast to the SQDG degradation, the synthesis of phosphatidylglycerol (PG), the other acidic lipid in chloroplast, is increased to elevate its content up to a level that just compensates for the loss of SQDG. This regulation was proposed to occur through direct sensing of SQDG-loss, but not of S-starvation, because of similar regulation of PG metabolism in an SQDG-deficient mutant under S-replete conditions. Moreover, photosystem I activity of thylakoid membranes isolated from S-starved wild-type cells was decreased in company with partial removal of PG on treatment with phospholipase A2, which implied that maintaining the total content of these acidic lipids contributes to the photosynthetic integrity under S-starved conditions.
