Effect of Water Stress on the Lipid and Fatty Acid Composition of Sweet Pepper (Capsicum annuum L.)

Sweet pepper ( Capsicum annuum L.) plants were grown under field irrigation and dryland conditions. Stress was imposed 12 d after planting by withholding water for 8 d, and seedlings were harvested for analysis 20 d after planting. In stressed plants, leaf water potential dropped from -0.65 to - 1.03 MPa and water saturation deficit increased by 40 %; plant height did not show a significant reduction. The fresh and dry weights of stressed seedlings and their ratio decreased. The total lipid and total phosphorus contents of stressed seedlings decreased by about 43 % and 71 %, respectively, in comparison to the contents of the watered seedlings. The diacylglycerol, free fatty acid and total polar lipid contents decreased significantly with stress, the last mentioned by more than 50 % in phospholipid levels. Glycolipid levels; were unchanged and the amount of triacylglycerol increase by about 30 % over the control.
Despite the differences found in the fatty acid composition of various lipid classes and between treatments, the degree of unsaturation did not change significantly either in control or stressed seedlings. Under stress conditions, free sterol levels increased without showing any change in the ratio of 'more planar' to 'less planar' sterols. The increase in free sterols and the decrease in phospholipid levels under water deficit conditions raised the sterol/phospholipid molar ratio 3-fold. The different responses of the lipid classes to water deficits and their possible significance are discussed.