Lipid content in higher plants under osmotic stress

In this work, we performed investigations on the lipid content of higher plants (spinach) under hyperosmotic stress, by means of thin layer chromatography (TLC) and mass spectrometry. In particular, the experiments have been performed at different plant organization levels: whole leaves, freshly prepared protoplast suspension and mesophyll cells obtained by reformation of the cell wall from protoplast suspension. The results obtained showed that hyperosmotic stress induces changes in the phospholipid content depending on the different plant organization levels studied. All phospholipids showed an increment of their content in stressed whole leaves. In particular, phosphatidylglycerol (PG) redoubles its content by 1 h of osmotic shock. Different responses to hyperosmotic stress were reported for the other systems. In the case of protoplasts, an increment of PG, phosphatidylcholine (PC) and phosphatidylinositol (PI) together with biphosphatidylglycerol (BPG) and phosphatidylethanolamine (PE) content decreasing were observed in stressed sample. For PG, identified as PG (34:4) by elecrospray ionization mass spectrometry, the increment was of about 30%. In the case of cells, conversely, a decrease of PG content under osmotic stress was recorded. The results suggest an important role of phospholipids, in particular of PG, in the osmotic stress response.