Oxidative damage to thylakoid proteins in water-stressed leaves of wheat (Triticum aestivum)

The production of reactive oxygen species in the chloroplast may increase u nder water deficit. To determine if this causes oxidative damage to the pho tosynthetic apparatus, nit analyzed the accumulation of oxidatively damaged proteins in thylakoids of a;ater-stressed wheat (Triticum aestivum L,) lea ves. Water stress was imposed on 4-week-old plants by withholding watering for 10 days to reach a soil water potential of about -2.0 MPa. In thylakoid s of,vater-stressed leaves there was an increase in oxidative damage, parti cularly in polypeptides of 68, 54, 41 and 24 kDa, High molecular mass oxidi zed (probably cross-linked) proteins accumulated in chloroplasts of drought ed leaves. Oxidative damage,vas associated with a substantial decrease in p hotosynthetic electron transport activity and photosystem II (PSII) efficie ncy (F-v/F-m), Treatment of stressed leaves with L-galactono-1,4-lactone (G L) increased their ascorbic acid content and enhanced photochemical and non -photochemical quenching of chlorophyll fluorescence, GL reduced oxidative damage to photosynthetic proteins of droughted plants, but it reverted the decrease in electron transport activity and PSII efficiency only partially, suggesting that other factors also contributed to loss of photosystem acti vity in droughted plants. Increasing the ascorbic acid content of leaves mi ght be an effective strategy to protect thylakoid membranes from oxidative damage in water-stressed leaves.