ACTION SPECTRA FOR LIGHT‐INDUCED DE‐EPOXIDATION AND EPOXIDATION OF XANTHOPHYLLS IN SPINACH LEAF*

Abstract

Abstract— The action spectra for violaxanthin de‐epoxidation and zeaxanthin epoxidation in New Zealand spinach leaf segments, Tetragonia expansa, were determined at equal incident quanta of 2·0 × 1015 quanta cm‐2 sec‐1. Precise action spectra were not obtained due to variable leaf activity. The de‐epoxidation action spectrum had major peaks at approximately 480 and 648 nm. Blue light was slightly more effective than red light and little activity was observed beyond 700 nm. The epoxidation action spectrum showed major peaks at around 440 and 670 nm. Blue light was more effective than red light and light beyond 700 nm showed definite activity.The net result of de‐epoxidation and epoxidation is a cyclic scheme, the violaxanthin cycle, which consumes O2 and photoproducts. The action spectra indicate that the violaxanthin cycle is more active in blue than in red light and therefore could account for O2 uptake stimulated by blue light. However, the violaxanthin cycle is not the pathway for O2 uptake by photosynthetic system 1. It was suggested that the violaxanthin cycle may function as a pathway for the consumption of excess photoproducts generated in blue light or the conversion of these photo‐products to other forms of energy.