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

alpha -Tocopherol (vitamin E) is a lipophilic antioxidant, which protects chloroplasts from oxidative damage. Diurnal variations in alpha -tocopherol, chlorophylls and carbon dioxide assimilation rates were measured during two consecutive summers to evaluate the photosynthetic response to drought and the protective role of alpha -tocopherol in 2- and 3-year-old lavender (Lavandula stoechas L.) plants grown under a Mediterranean climate. Lavender plants showed one-peaked diurnal time courses of photosynthesis and progressive decreases in the carbon dioxide assimilation rates as drought progressed during the summer. In severe stress and when photosynthesis was highly reduced, 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 oxidative stress. However, lavender plants did not suffer from photoinhibitory damage throughout the experiment, indicating the contribution of alpha -tocopherol (in addition to other possible mechanisms) in the protection of chloroplasts from drought-induced oxidative damage.