Effects of phosphate deficiency on the lipid composition in cucumber thylakoid membranes and PSII particles

Phosphatidylglycerol (PG) is the sole phospholipid in thylakoid membranes. Phosphate deficiency clearly affected the thylakoid membrane lipid composition of cucumber leaves. Phosphate deficiency induced the decrease in PG content and the concomitant increases in the content of digalactosyl diacylglycerol (DGDG) and sulfoquinovosyl diacylglycerol (SQDG) in cucumber leaves. Although phosphate deficiency led to the 44mol% decrease of thylakoid PG, the chlorophyll fluorescence coefficients and photosystem 11 (PSII) oxygen-evolving activity under phosphate deficiency showed virtually no difference compared with those under phosphate sufficiency. It was suggested that phosphate deficiency had no clear effect on PSII function. Besides, PG still maintained in a high level in PSII under phosphate-deficient conditions. These results showed that phosphate deficiency could result in PG decrease in some thylakoid membrane domains but had little effect on the content of PG existed in PSII membrane domains of thylakoid. Maybe, there were two types of PG in thylakoid membrane. Some PG molecules only played a role in the structure of thylakoid membrane and other lipid molecules such as SQDG can substitute for them under phosphate deficiency while some PG molecules may play an important role in maintaining the structure and function of PSII and other lipid molecules cannot substitute for them.(C) 2004 Elsevier Ireland Ltd. All rights reserved.