Role of photoprotective systems of holm-oak (Quercus ilex) in the adaptation to winter conditions

Helm-oak (Quercus ilex L.) is a Mediterranean evergreen sclerophyllous spec ies adapted to a wide range of environmental conditions and consequently it s leaves must be able to withstand variable stresses. Changes in pigment an d antioxidant composition were assessed in relation to chilling stress, lig ht environment and leaf aging. Photosynthetic capacity during winter was tw o-fold higher than in spring. However, the photochemical efficiency of PSII was reduced in sun leaves probably because of an increased rate of thermal energy dissipation related to the superior zeaxanthin concentration. Lutei n, neoxanthin, beta-carotene and the xanthophyll cycle pool increased durin g winter especially in sun leaves, while lutein epoxide and alpha-carotene decreased markedly. The main antioxidant accumulated during winter was asco rbate, while glutathione and alpha-tocopherol were not seasonally affected. Catalase increased in spring as a consequence of higher photorespiration r ates, while GR and MDHAR activities were higher in sun leaves during winter . The high MDHAR activity indicates an important role for this enzyme in th e adaptation to environmental factors associated to winter. The present stu dy demonstrates that helm-oak is able to acclimate to a variety of environm ental stress factors by inducing dramatic changes in their photosynthetic c haracteristics, Figment composition and antioxidant defences.