Profiling membrane lipids in plant stress responses -: Role of phospholipase Dα in freezing-induced lipid changes in Arabidopsis

A sensitive approach based on electrospray ionization tandem mass spectrometry has been employed to profile membrane lipid molecular species in Arabidopsis undergoing cold and freezing stresses. Freezing at a sublethal temperature induced a decline in many molecular species of phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidylglycerol (PG) but induced an increase in phosphatidic acid (PA) and lysophospholipids. To probe the metabolic steps generating these changes, lipids of Arabidopsis deficient in the most abundant phospholipase D, PLDalpha, were analyzed. The PC content dropped only half as much, and PA levels rose only half as high in the PLDalpha-deficient plants as in wild-type plants. In contrast, neither PE nor PG levels decreased significantly more in wild-type plants than in PLDa-deficient plants. These data suggest that PC, rather than PE and PG, is the major in vivo substrate of PLDalpha The action of PLDalpha during freezing is of special interest because Arabidopsis plants that are deficient in PLDalpha have improved tolerance to freezing. The greater loss of PC and increase in PA in wild-type plants as compared with PLDalpha-deficient plants may be responsible for destabilizing membrane bilayer structure, resulting in a greater propensity toward membrane fusion and cell death in wild-type plants.