Effects Of Exogenous Glycinebetaine On The Composition And Function Of Thylakoid Membrane Of Wheat Leaves Under Drought And Salt Stress

Two wheat cultivars (Triticum aestivum L.), HF9703 tolerant to drought and SN215953 sensitive to drought, were used to study the effects of glycinebetaine on the composition and function of thylakoid membrane. In seedling experiments, the Hoagland solution containing 1.5 mmol/l GB (Sigma) (CK no containing GB) was used to culture seedlings for three days (culture solution was changed everyday). Drought stress was imposed by Hoagland solution containing 15% PEG-6000 for two days (salt stress using Hoagland solution containing 100mmol/L NaCl). The second fully expanded leaves were taken for measurements. In field experiments, drought stress was imposed by withholding irrigation from elongating stage (CK were irrigated once a week). For GB treatment, the drought-stressed plants grew till grain-filling stage and then aqueous 100 mmol/L GB (Sigma) containing 0.1% Tween 20 was sprayed with an atomizer to the leaves until runoff twice a day for 3 days. The non-GB applied plants were sprayed with water containing 0.1% Tween 20. The flag leaves were taken for measurements. The main results are as follows: 1. Effects of exogenous glycinebetaine on the composition of thylakoid membrane lipid of wheat leaves under osmotic stress (1) Effects of root-applied glycinebetaine on lipid content in the thylakoid membrane of wheat leaves under drought stress The monogalactosyl diaylglycerol (MGDG), digalactosyl diacylglycerol (DGDG) and phosphatidylglycerol (PG) contents of the two wheat cultivars decreased significantly under drought stress; the sulfoquinovosyl diacylglycerol (SQDG) content in HF9703 increased significantly, while in SN215953, the SQDG content decreased significantly under drought stress. GB treatment maintained their contents as CK. (2) Effects of exogenous glycinebetaine on the composition of thylakoid membrane fatty acids of wheat leaves under osmotic stress The degree of saturated fatty acid in MGDG and SQDG and the trans-hexadecenoic (16:1(3t)) content of HF9703 increased significantly under drought stress, while those changes of SN215953 were opposite. These results indicated that HF9703 was more adaptable to drought stress than SN215953. Exogenous glycinebetaine could maintain the fatty acid contents in thylakoid membrane of wheat under drought stress as CK. Oppositely, under salt stress, the main changes of fatty acid content were the increase of saturated fatty acid in PG & PC, and root-applied glycinebetaine diminished these changes. 2. Effects of exogenous glycinebetaine on the structure and function of thylakoid membrane of wheat under osmotic stress ( 1 ) Effects of foliar-applied betaine on thylakoid lamella ultrastructure of wheat flag leaves under drought stress Thylakoid lamella of wheat flag leaves became swollen and difficult to distinguish under drought stress, and those changes were more significant in SN215953 than in HF9703. Foliar-applied glycinebetaine could protect thylakoid lamella of wheat flag leaves from drought stress. (2)Effects of exogenous glycinebetaine on function of protein complexes in thylakoid membrane of wheat flag leaves under osmotic stress...