Effects of excessive photon on the photosynthetic pigments and violaxanthin de-epoxidase activity in the xanthophyll cycle of spinach leaf

Excessive photon effects on the photosynthetic pigments and violaxanthin de-epoxidase activity in the xanthophyll cycle of two-month-old spinach leaves were investigated. The leaves were exposed to an excessive photon flux of 1300 μmol m−2 s−1 for 24 h. Photosynthetic pigments such as chlorophylls and carotenoids were quantified and purified by high-performance liquid chromatography. The results showed that the high irradiance induced the dynamic conversion of photosynthetic pigments, and that a higher ratio of zeaxanthin/total chlorophyll was built up. The reactions with photosystem 2 (PS2) particles supplemented with violaxanthin de-epoxidase and Tween 20 at 30 °C for 3 h resulted in a decrease in violaxanthin and an increase in antheraxanthin and zeaxanthin, as compared to reactions carried out in the absence of violaxanthin de-epoxidase, using PS2 particles isolated from normal and high irradiance-illuminated leaves. Lutein was taken as an internal standard among xanthophylls because it remained constant. In the high irradiance-illuminated leaf, for the reactions of PS2 particles in the absence of violaxanthin de-epoxidase and in the presence of violaxanthin de-epoxidase supplemented with Tween 20, their de-epoxidation indexes were similar to the reaction determined in the presence of violaxanthin de-epoxidase from the leaves that were kept at the light intensity of 15 μmol m−2 s−1, reflecting the promotive effects of excessive photon as well as Tween 20 on violaxanthin de-epoxidase activity.