Ultraviolet-absorbing/screening substances in cyanobacteria, phytoplankton and macroalgae

Continuous depletion of the stratospheric ozone layer has resulted in an increase in ultraviolet-B (UV-B; 280-315 nm) radiation reaching the Earth's surface. UV radiation has been reported to suppress a number of photochemical and photobiological processes in a wide variety of organisms. However, certain 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 quenchers and antioxidants, an important mechanism by which organisms prevent UV-induced photodamage is the synthesis of UV-absorbing/screening substances such as mycosporine-like amino acids (MAAs) and the cyanobacterial sheath pigment, scytonemin. This review covers the occurrence of these UV-absorbing/screening compounds in three different classes of organism, namely, cyanobacteria, phytoplankton and macroalgae, and their role in mitigating UV toxicity. (C) 1998 Elsevier Science S.A. All rights reserved.