Lipid Changes in Maize Seedlings in Response to Field Water Deficits

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Abstract
Maize seedlings (Zea mays hybrid F1 Montano) were grown under field irrigation and dryland conditions. Stress was imposed 12 d after planting by witholding water for 8 d, and seedlings were harvested for analysis 20 d after planting. In comparison to the control, leaf water potential drops from −0.65 to −1.03 MPa and water saturation deficit increases by 40%, but plant height does not show a significant reduction. The fresh and dry weights of stressed seedlings and their ratio decrease. The total lipid and total lipid phosphorus contents of seedlings exposed to dryland conditions decrease 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 decrease significantly with stress, but in the latter class the dryland conditions induce a decrease of more than 50% in phospholipid levels, whereas they do not cause any change in glycolipid levels; on the contrary, the triacylglycerol amount increases by about 30% over the control. Notwithstanding differences found in the fatty acid composition of the various lipid classes and between treatments, the degree of unsaturation never changes significantly either in the control or in the stressed seedlings. Under stress conditions, free sterol levels increase without showing any change in the ratio of ‘more planar’ to ‘less planar’ sterol. The increase in free sterols and the decrease in phospholipid levels under water deficit conditions raise the sterol/phospholipid molar ratio 3-fold. The different responses of the lipid classes to water deficits and their possible significance are discussed.