Diurnal patterns of α-tocopherol accumulation in Mediterranean plants

Diurnal variations in α-tocopherol were evaluated in combination with different indicators of stress in seven plant species grown under Mediterranean field conditions. The species studied were a gymnospern, Pinus pinea L., and six angiosperms, Quercus suber L. (Fagaceae), Cistus clusii Dunal and Cistus albidus L. (Cistaceae), Rosmarinus officinalis L, Salvia officinalis L. ssp. major and Melissa officinalis L. (Labiatae). Contrasting patterns of diurnal variations in α-tocopherol during the summer were observed in plants, mainly related to their degree of stress resistance. While both trees (P. pinea and Q. suber) and C. albidus displayed increases of α-tocopherol at midday, the contents of this antioxidant kept constant throughout the day in C. clusii and R. officinalis, and decreased significantly at midday in S. officinalis and M. officinalis. This midday depression of α-tocopherol may be indicative of the sensitivity of these latter species to high light during the summer drought characteristic of the Mediterranean climate.