CAROTENOID COMPOSITION AND METABOLISM IN GREEN AND BLUE-GREEN-ALGAL LICHENS IN THE FIELD

The carotenoid composition of 33 species of green algal lichens and 5 species of blue-green algal lichens was examined and compared with tha t of the leaves of higher plants. As in higher plants, green algal lic hen species which were found in both shade and full sunlight exhibited higher levels of the carotenoids involved in photoprotective thermal energy dissipation (zeaxanthin as well as the total xanthophyll cycle pool) in the sun than in the shade. This was particularly true when th alli were moist during exposure to high light, or presumably became de siccated in full sunlight. However, the reverse trend in the carotenoi d composition of green algal lichens was also observed in those specie s which were found predominantly either in the shade or in full sunlig ht. In this case sun-exposed lichens often possessed lower levels of z eaxanthin and of the components of the xanthophyll cycle than lichens which were found in the shade. In contrast to higher plants, the liche ns from all habitats exhibited a relatively high ratio of carotenoids to chlorophylls (more characteristic of sun leaves), very low levels o f alpha-carotene (similar to that found in sun leaves), and a level of beta-carotene similar to that found in shade leaves. Zeaxanthin, but not the epoxides of the xanthophyll cycle, was also frequently found i n blue-green algal lichens. A trend for increasing levels of zeaxanthi n with increasing growth light regime was observed in Peltigera rufesc ens, the species which was found to occur over the widest range of lig ht environments. The level of zeaxanthin per chlorophyll a in these bl ue-green algal lichens was in a range similar to that per chlorophyll a + b in green algal lichens. However, zeaxanthin was also absent in o ne species, Collema cristatum. in full sunlight. Thus, the zeaxanthin content of the blue-green algal lichens can be similar to that of high er plants, or it can be rather dissimilar, as was also the case in the green algal lichen species. The presence of large amounts of ketocaro tenoids in blue-green algal lichens is also noteworthy.