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 species adapted to a wide range of environmental conditions and consequently its leaves must be able to withstand variable stresses. Changes in pigment and antioxidant composition were assessed in relation to chilling stress, light environment and leaf aging. Photosynthetic capacity during winter was two-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. Lutein, neoxanthin, beta-carotene and the xanthophyll cycle pool increased during winter especially in sun leaves, while lutein epoxide and alpha-carotene decreased markedly. The main antioxidant accumulated during winter was ascorbate, while glutathione and alpha-tocopherol were not seasonally affected. Catalase increased in spring as a consequence of higher photorespiration rates, while GR and MDHAR activities were higher in sun leaves during winter. The high MDHAR activity indicates an important role for this enzyme in the adaptation to environmental factors associated to winter. The present study demonstrates that helm-oak is able to acclimate to a variety of environmental stress factors by inducing dramatic changes in their photosynthetic characteristics, Figment composition and antioxidant defences.