THE EFFECTS OF ILLUMINATION ON THE XANTHOPHYLL COMPOSITION OF THE PHOTOSYSTEM-II LIGHT-HARVESTING COMPLEXES OF SPINACH THYLAKOID MEMBRANES

The xanthophyll composition of the light-harvesting chlorophyll alb proteins of photosystem II (LHCII) has been determined for spinach (Spinacia oleracea L.) leaves after dark adaptation and following illumination under conditions optimized for conversion of violaxanthin into zeaxanthin. Each of the four LHCII components was found to have a unique xanthophyll composition. The major carotenoid was lutein, comprising 60% of carotenoid in the bulk LHCIIb and 35 to 50% in the minor LHCII components LHCIIa, LHCIIc, and LHCIId. The percent of carotenoid found in the xanthophyll cycle pigments was approximately 10 to 15% in LHCIIb and 30 to 40% in LHCIIa, LHCIIc, and LHCIId. The xanthophyll cycle was active for the pigments bound to all of the LHCII components. The extent of deepoxidation for complexes prepared from light-treated leaves was 27, 65, 69, and 43% for LHCIIa, -b, -c, and -d, respectively. These levels of conversion of violaxanthin to zeaxanthin were found in LHCII prepared by three different isolation procedures. It was estimated that approximately 50% of the zeaxanthin associated with photosystem II is in LHCIIb and 30% is associated with the minor LHCII components.