Abstract:

Previous studies on responses of plants to drought stress were mostly performed with young plant seedlings subjected to experimental stress. Experimental stresses are usually abruptly imposed on plants. However, in the drought field, plants are subjected to gradual stress because water availability in the soil does not change quickly. Therefore, responses of plants might be different under the two stress conditions. The plasma membrane is very sensitive to drought, which causes alteration of its structure and functions. To our knowledge, few studies concerning the effects of gradual field drought on properties of the plasma membrane in the course of whole developmental stages have been published. In the present work, we took two spring wheat (Triticum aestivum) as materials and investigated changes in plant growth, fatty acid composition of polar lipids and activities of key enzymes in the plasma membranes of leaves under gradual field drought. Drought stress decreased water content of wheat leaves and inhibited plant growth. At early developmental stages, drought stress decreased fatty acid unsaturation of polar lipids in the plasma membranes, membrane protein content and activities of H+-ATPase (EC 3.6.1.35), while it increased 5'-AMPase (EC 3.1.3.5) activity and O2 resumption by plasma membranes. At late developmental stages, with drought progressing, membrane protein content and H+-ATPase activities were increased by continuing drought, and fatty acid unsaturation of polar lipids in the plasma membranes was increased or not significantly changed, whereas 5'-AMPase activities and O2 resumption by plasma membranes were decreased. These results suggest that wheat plants are sensitive to drought at early developmental stages, and the fluidity of plasma membranes as well as energy reservoirs decrease. At late stages, adaptive phenomena of plants to drought were observed. Our results might be able to help elucidate plant drought resistance under natural drought conditions.