Abstract
In deciduous trees, immature leaves in early spring and senescing leaves in autumn have low photosynthetic activity. In addition, they sometimes suffer from low temperature in cool temperate forests. To examine whether defensive responses to photo-oxidative stress are observed in such leaves, we harvested leaves of 5 deciduous tree species from the experimental forests of Hokkaido Forestry Research Institute once in every month from May to October for 3 years. Xanthophyll cycle pool size was larger in early spring and autumn. Changes in de-epoxidation rate of xanthophyll cycle were different among species and years, however, the de-epoxidation rate was higher in autumn, especially in broad leaved species. Membrane-bound APX activity was relatively higher in early spring and increased in autumn. These results suggest that xanthophyll cycle and APX activity involve in defensive responses to photo-oxidative stress in immature leaves in early spring and senescing leaves in autumn.
