Abstract
Antioxidative enzyme activities and contents of chlorophyll, carotenoid and flavonoid in leaves of Cattleya and Cymbidium exposed to 40%, 70% and full (100%) sunlight for 80 days from August 1 were examined. Results obtained were compared with our previous data for the same orchids exposed to different irradiance from May 1. Antioxidative mechanisms of these orchids attributed to adaptation to sunlight with high intensity would be dependent on the season before and during adaptation. The chlorophyll contents in both orchids decreased by light of high intensities in both seasons (August and May), though changes in carotenoid and flavonoid contents were different in plant species and depended on light intensity. High protein content, dry matter concentration of the leaves and percentage of flowering indicate a possible relation with antioxidative function, that is the function of protection against strong light-induced injuries.
