Water deficit in combination with high solar radiation leads to midday depression of alpha-tocopherol in field-grown lavender (Lavandula stoechas) plants

alpha -Tocopherol (vitamin E) is a lipophilic antioxidant, which protects c hloroplasts from oxidative damage. Diurnal variations in alpha -tocopherol, chlorophylls and carbon dioxide assimilation rates were measured during tw o consecutive summers to evaluate the photosynthetic response to drought an d the protective role of alpha -tocopherol in 2- and 3-year-old lavender (L avandula stoechas L.) plants grown under a Mediterranean climate. Lavender plants showed one-peaked diurnal time courses of photosynthesis and progres sive decreases in the carbon dioxide assimilation rates as drought progress ed during the summer. In severe stress and when photosynthesis was highly r educed, the chlorophyll content of leaves decreased. Midday depressions of alpha -tocopherol were observed when high solar radiation was superimposed on water deficit, indicative of the susceptibility of lavender plants to ox idative stress. However, lavender plants did not suffer from photoinhibitor y damage throughout the experiment, indicating the contribution of alpha -t ocopherol (in addition to other possible mechanisms) in the protection of c hloroplasts from drought-induced oxidative damage.