Ultraviolet-absorbing/screening substances in cyanobacteria, phytoplanktonand macroalgae

Continuous depletion of the stratospheric ozone layer has resulted in an in crease in ultraviolet-B (UV-B; 280-315 nm) radiation reaching the Earth's s urface. UV radiation has been reported to suppress a number of photochemica l and photobiological processes in a wide variety of organisms. However, ce rtain photosynthetic organisms which are exposed simultaneously to visible and UV radiation in their natural environment have developed mechanisms to counteract the damaging effects of UV. Besides repair of UV-induced damage of DNA and accumulation of carotenoids and detoxifying enzymes or radical q uenchers and antioxidants, an important mechanism by which organisms preven t UV-induced photodamage is the synthesis of UV-absorbing/screening substan ces such as mycosporine-like amino acids (MAAs) and the cyanobacterial shea th pigment, scytonemin. This review covers the occurrence of these UV-absor bing/screening compounds in three different classes of organism, namely, cy anobacteria, phytoplankton and macroalgae, and their role in mitigating UV toxicity. (C) 1998 Elsevier Science S.A. All rights reserved.