Abstract

The effect of repeated water-deficit stress on the lipid composition of root cells from 5-day-old oat (Avena sativa L. cv. Seger) seedlings was studied. The content of total acyl lipids was found to decrease with increasing degree of water-deficit stress, owing largely to decreases in free fatty acids, triglycerides, phosphatidylethanolamine (PE), wax esters, steryl esters, and acylated steryl glycosides. Major polar lipids both in total root cells and in the plasma membrane enriched fraction, as well as the microsomal membrane fraction, were PE, phosphatidylcholine (PC), digalactosyldiacylglycerol (DGDG), monogalactosyldiacylglycerol (MGDG), and polyglycolipid. Decreases in the degree of unsaturation of the fatty acids as a funtion of increased water-deficit stress were observed for the MGDG and polyglycolipid components of total root cells and for the MGDG, DGDG, and polyglycolipid of the plasma membrane fraction. Electron microscopy showed that stressed root tip cells had much smoother plasma membranes than those of control unstressed root cells. These results suggest that root cells of oat seedlings respond to water-deficit stress by reducing the total plasma membrane mass and degree of lipid fluidity, which would reduce the water permeability of the plasma membranes and help maintain cell turgidity.

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