CAROTENOID COMPOSITION IN GREEN LEAF AND STEM TISSUE OF THE CAM-PLANTCISSUS-QUINQUANGULARIS CHIOV

The composition of the photosynthetic pigments (chlorophylls and carot enoids) was investigated in leaf and stem tissue of the CAM species Ci ssus quinquangularis Chiov. grown at a sun-exposed site in the summer 1993. Significant differences were not found between leaves and stems concerning the level of chlorophyll a and b and the total carotenoids. In addition most individual carotenoids also ranged within similar va lues for leaf and stem tissue. The sum of the xanthophyll cycle carote noids violaxantin, antheraxanthin and zeaxanthin was, however, signifi cantly higher in the stem as compared to the leaf tissue. At low-light conditions or after a 12 h dark period the stem tissue always exhibit ed a significantly higher zeaxanthin content than that found in the le af. There were no significant differences concerning the ratios of pre nylpigments, except for the ratio chlorophyll al carotene, which was s ignificantly lower in the leaf (18.8) as compared to the stem (23.1). The pigment ratios of the CAM-plant Cissus quinquangularis are, howeve r, somewhat different from C-3-plants. The performance of the violaxan thin/zeaxanthin cycle was investigated in leaf and stem tissue by givi ng a 1h high-light treatment (1400 mu mol m(-2).s(-1)) after a 12-hour dark period. The results indicate that the violaxanthin/zeaxanthin cy cle, which is assumed to be involved in the protection of photosynthet ic apparatus against excess light energy, is active in the leaf as wel l as in the stem tissue. The photoconversion of violaxanthin to zeaxan thin, however, proceeded in all samples from different Cissus plants t o a significantly higher extent in leaf than in stem tissue. Correspon dingly, upon high-light treatment, the deepoxidation state DEPS of the violaxanthin/zeaxanthin cycle carotenoids increased 3.2 times in leaf and only 2.4 times in stem tissue.