Desiccation Tolerance in Maturing Maize Seed: Membrane Phospholipid Composition and Thermal Properties
Membrane phospholipids play an important role in acclimation of plants to environmental stresses. Phospholipid composition and thermal properties in maturing maize (Zea mays L.) seed were studied to relate high-temperature desiccation tolerance to membrane stabilization. A preconditioning process (treatment at 35 °C prior to high-temperature drying) was used to induce the high-temperature desiccation tolerance. Phosphatidylcholine (PC) accumulated, resulting in an increase in the PC/phosphatidylethanolamine (PE) ratio from 3.6 to 8 within 48 h as the high-temperature desiccation tolerance was induced during preconditioning. The increase in PC/ PE ratio coincided with a decrease in both phase transition temperature and enthalpy of transition, indicating more stable membranes. The improved stability could be related to the high-temperature desiccation tolerance and membrane function after preconditioning. A shift in the fatty acid composition of the membrane lipids from linoleic acid (18:2) to oleic acid (18:1) during preconditioning indicates a more saturated fatty acid composition. This shift in fatty acids may result in membranes that more easily cope with high-temperature desiccation, as contrasted to a low-temperature effect. The results suggest that alterations in phospholipid molecular species and changes in fatty acid composition to a more saturated composition in maize seed during preconditioning and maturation could be common mechanisms in high-temperature desiccation tolerance.
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