STRATEGIES OF ULTRAVIOLET-B PROTECTION IN MICROSCOPIC ALGAE

Different species of microalgae show a wide range of susceptibility to ultraviolet-B (UV-B) radiation. To identify factors responsible for t he UV-B tolerance of some of the algae, we compared 8 species that are highly tolerant to UV-B to 8 species that are highly susceptible. The tolerant species contained substantial amounts of an acetolysis -resi stant residue. The residue consists of sporopollenin, a biopolymer of variable chemical composition that occurs in the algal cell walls and absorbs UV-B radiation. The susceptible species contained little or no sporopollenin. We propose that sporopollenin provides protection to t he tolerant species by screening the incident UV-B radiation. Previous studies showed that the mycosporine-like amino acids (MAA) also act a s effective UV-B screens. Our data indicate that sporopollenin provide s a constant protection while MAA are induced by radiation stress and occur with some delay. The tolerant species also differ front the susc eptible species in their capacity to repair the reaction centers damag ed by UV-B, The tolerant algae became vulnerable to UV-B when protein synthesis needed for repair was blocked by streptomycin. In the suscep tible species, streptomycin had no effect during the UV-B stress, The repair deficiency in the susceptible species can be explained either b y relatively less effective protein synthesis or by an inhibition of t he protein synthesis by UV-B. Ln the tolerant species, the structures needed for protein synthesis are protected by UV-B screening of sporop ollenin and MAA.