Salinity and hyperosmotic stress induce rapid increases in phosphatidylinositol 4,5-bisphosphate, diacylglycerol pyrophosphate, and phosphatidylcholine in Arabidopsis thaliana cells

In animal cells, phosphoinositides are key components of the inositol 1,4,5 -trisphosphate/diacylglycerol-based signaling pathway, but also have many o ther cellular functions. These lipids are also believed to fulfill similar functions in plant cells, although many details concerning the components o f a plant phosphoinositide system, and their regulation are still missing. Only recently have the different phosphoinositide isomers been unambiguousl y identified in plant cells. Another problem that hinders the study of the function of phosphoinositides and their derivatives, as well as the regulat ion of their metabolism, in plant cells is the need for a homogenous, easil y obtainable material, from which the extraction and purification of phosph olipids is relatively easy and quantitatively reproducible. We present here a thorough characterization of the phospholipids purified from [P-32]ortho phosphate- and myo-[2-H-3]inositol-radiolabded Arabidopsis thaliana suspens ion-cultured cells. We then show that NaCl treatment induces dramatic incre ases in the levels of phosphatidylinositol 4,5-bisphosphate and diacylglyce rol pyrophosphate and also affects the turnover of phosphatidylcholine. The increase in phosphatidylinositol 4,5-bisphosphate was also observed with a non-ionic hyperosmotic shock. In contrast, the increase in diacylglycerol pyrophosphate and the turnover of phosphatidylcholine mere relatively speci fic to salt treatments as only minor changes in the metabolism of these two phospholipids were detected when the cells were treated with sorbitol inst ead of NaCl.