Lipid peroxidation and α-tocopherol content in α-tocopherol-supplemented thylakoid membranes during UV-B exposure

Spinach thylakoid membranes were supplied with exogenous alpha-tocopherol to determine if elevated alpha-tocopherol levels would protect lipids from degradation induced by UV-B radiation exposure. During the thylakoid isolation procedure: exogenous alpha-tocopherol was added to a volume of thylakoids resulting in an approximately 6-fold increase above endogenous alpha-tocopherol concentrations. The normal (thylakoids with unamended tocopherol levels) and high alpha-tocopherol membranes were then irradiated for 180 min at 25 degrees C with either 1.8 kJ m(-2) h(-1) of biologically In effective UV-B (UV-B-BE) radiation or 350 mu mol m(-2) s(-1) of photosynthetically active radiation (PAR). A volume of thylakoids kept in the dark served as a DARK control. Lipid peroxidation and alpha-tocopherol content were measured on a chlorophyll basis at 0, 90 and 180 min of radiation exposure. In normal thylakoids, both UV-B and PAR increased lipid peroxidation over lime with PAR inducing more lipid damage than UV-B at 90 and 180 min. Lipid peroxidation did not increase above DARK control levels during the exposure period for either the UV-B-or PAR-exposed thylakoids in the high alpha-tocopherol treatments. Although alpha-tocopherol levels were not altered by either UV-B or PAR in the normal thylakoids, they declined similarly for both radiation treatments at 90 and 180 min of exposure in the high tocopherol membranes. These data indicate that elevated levels of alpha-tocopherol conferred antioxidant protection to UV-B-and PAR-exposed thylakoid membrane lipids but al the cost of significant alpha-tocopherol degradation over time. (C) 1998 Elsevier Science B.V. All rights reserved.