| Phosphatidylglycerol(PG) is the sole phospholipid existing in thylakoid membrane and thylakoid PG has particular structure, with palmitic acid(16: 0) or A 3-trans-hexadecenoic(16:1t) esterified at sn-2 position of glycerol. It has been demonstrated by many workers that PG plays an important role in structure and function of thylakoid membranes. However, it has been shown that phosphate deficiency strongly affected lipid composition of the thylakoid membrane by decreasing the relative content of PG and increasing that of digalactosyl diacylglycerol (DGDG) and sulfoquinovosyl diacylglycerol (SQDG) in cyanobacteria, Chlamydomonas and Arobidopsis thaliana. These results show that under phosphate deficient conditions DGDG and SQDG can substitute for PG In this study, we analyzed the effects of phosphate deficiency on the lipid composition, especially on PG in wheat leaves as well as in cucumber leaves, thylakoid membrane and PSII particles in order to clarify the relation between PG and other lipids and the role of PG in thylakoid membrane.Wheat plants were grown in phosphate-deficient and phosphate-sufficient conditions, respectively, and lipid composition in leaves of 9-day-old as well as 16-day-old plants was analyzed. We found that phosphate deficiency induced a dramatic change in the lipid levels in photosynthetic membranes of wheat leaves and the extent of changes in lipid composition depended on the leaf ages. Phosphate deficiency induced a gradual decrease in PG and monogalactosyl diacylglycerol (MGDG) and a concomitant increase in DGDG and SQDG from the first leaf to the second and the third leaf on 16-day-old plants. In addition, as compared to leaves grown under phosphate sufficient solution, PG content in the first leaf of 16-day-old plants was significantly lower than that of 9-day-old leaf with 2.5 mol % versus 5.5 mol % when these plants were grown under phosphate deficient condition. These results suggest that the alternation in lipid coniposition in wheat leaves induced by phosphate deficiency be related to both lipid biosynthesis and PG degradation. PG decrease in younger leaves is mainly due to insufficient phosphate supply for PG biosynthesis,while PG degradation mainly resulted in the PG decrease in older leaves.It is well known that all PG in leaves are not distributed in thylakoid membranes. Besides, PG is the sole phospholipid in thylakoid membrane. Therefore, in order to demonstrate the effect of phosphate deficiency on the lipid composition in thylakoid membrane, we extracted thylakoid membrane and PSII particles from cucumber leaves, which were obtained from cucumber plants grown in Hoagland solutions containing 1.0 mM phosphate (control) or 0.01 mM(low Pi) and then analyzed lipid composition, respectively. The results are as followed:1. Phosphate deficiency induced a decrease in all phospholipid and a concomitant increase in DGDG and SQDG in cucumber leaves.2. The content of phospholipid in leaves gradually decreased in accompany with the increase of leaf age under phosphate deficient conditions. And phosphatidylcholine (PC) and phosphatidylethanolamine (PE) in younger leaves decreased by more extent as compared to PG while PG had a more clear decrease in younger leaves than in older ones. PC and PE are the major constitutes of plasma membrane, ER membrane and miochondria membrane while PG is mainly located in thylakoid membrane. Therefore, it is shown from these results that phosphate deficiency exerted more influence on extraplastidic membrane than on thylakoid membrane and phosphate in phospholipids could be transported from older leaves to younger ones to be reutilized by younger leaves.3. The changes of lipid composition in thylakoid membrane caused by phosphate deficiency were similar to those in leaves-PG decrease were accompanied with increase of DGDG and SQDG However, phosphate deficiency resulted in thylakoid MGDG decrease. During the plant growth, PG in thylakoid membrane of older leaves had a more obvious decrease than that in thylakoid membra...
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