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

The composition of the photosynthetic pigments (chlorophylls and carotenoids) was investigated in leaf and stem tissue of the CAM species Cissus 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 values for leaf and stem tissue. The sum of the xanthophyll cycle carotenoids violaxantin, antheraxanthin and zeaxanthin was, however, significantly 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 exhibited a significantly higher zeaxanthin content than that found in the leaf. There were no significant differences concerning the ratios of prenylpigments, except for the ratio chlorophyll al carotene, which was significantly lower in the leaf (18.8) as compared to the stem (23.1). The pigment ratios of the CAM-plant Cissus quinquangularis are, however, somewhat different from C-3-plants. The performance of the violaxanthin/zeaxanthin cycle was investigated in leaf and stem tissue by giving 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 cycle, which is assumed to be involved in the protection of photosynthetic apparatus against excess light energy, is active in the leaf as well as in the stem tissue. The photoconversion of violaxanthin to zeaxanthin, however, proceeded in all samples from different Cissus plants to a significantly higher extent in leaf than in stem tissue. Correspondingly, 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.