Changes in membrane lipid and free fatty acid composition during low temperature preconditioning against SO2 injury in coleus.

The effects of a low temperature (13 degrees C) treatment known to provide protection against sulphur dioxide (SO2) injury were assessed on leaf lipid composition in two cultivars of Coleus blumei Benth, found previously to differ in sensitivity to SO2 and other environmental stresses. After 5 days growth at 13 degrees C, there were significant differences in membrane lipid fatty acid composition as well as in free fatty acid (FFA) levels between SO2-sensitive 'Buckley Supreme' ('BS') and SO2-insensitive 'Marty' ('M'). Molecular species of chloroplast galactolipids in 'M' contained increased levels of linolenic acid (18:3). In the leaf FFA pools, the saturated components, palmitic (16:0) and stearic (18:0) acids, were predominant at 20 degrees C. After temperature hardening at 13 degrees C, the total amount of FFAs decreased in 'M' but increased in 'BS.' These modifications in lipid composition suggest an additional mechanism for cultivar differences in tolerance to SO2 and other stressors in coleus.