COMPARATIVE-STUDIES ON XANTHORIA-PARIETINA, A POLLUTION-RESISTANT LICHEN, AND RAMALINA-DURIAEI, A SENSITIVE SPECIES .2. EVALUATION OF POSSIBLE AIR POLLUTION-PROTECTION MECHANISMS

Surveys of the distribution of the lichens Xanthoria parietina and Ram alina duriaei in Israel showed that environments with air pollution ha d no damaging effects on X. parietina, whereas R. duriaei had disappea red from polluted environments: physiological studies supported this r elative sensitivity. Investigations of possible defence mechanisms pro tecting X. parietina from the damaging effects of air pollution showed a multitude of possible protective systems. These included constituti ve avoidance such as: efficient buffering capacity; a relatively high potassium content; and antioxidation by parietin, and induced toleranc e such as: SO2 oxidation to non-toxic sulphate; increased glutathione content; induced proline and arginine synthesis; and increased detoxif ication of active oxygen forms. (C) 1996 The British Lichen Society