Effect of UV-B Radiation (290-320nm) on the Nitrogen Metabolism of Several Marine Diatoms.

The marine diatoms Bellerochea yucatanensis, Biddulphia sinensis, Ditylum brightwellii, Lauderia annulata and Thalassiosira rotula were grown for 2 days under different levels of UV-B radiation (439, 717, and 1230J · m (-2) ·d(-1)). UV-B stress depressed the growth rates of all species. A low UV-B dose (439 J · m (-2) · d (-1), weighted), usually caused a slight increase in biomass production (dry weight} in comparison to nontreated cells. Enhanced UV-B reduced the dry matter productivity of all diatoms. All marine diatoms exposed to UV-B showed a diminution of protein and pigment content (chlorophyll a, chlorophyll c(1) + C(2), and carotenoids). Algae grown in 20 %o or 35 %o salt concentrations were more sensitive to UV-B radiation than those grown in 45%o. S. The effect of higher UV-B dose (717J · m (-2) · d(-1), weighted) upon the pools of free amino acids was species-dependent. Aspartate and asparagine levels were reduced in all diatoms. A marked increase in glutamine levels was found in Bellerochea, Biddulphia, Ditylum and Lauderia. Thalassiosira cells exposed to UV-B showed a significant increase in glutamate levels and a reduction of glutamine levels. (15)N and (14)C incorporation into several amino acids was reduced by exposure to UV-B. The results are discussed with reference to the inhibition of the enzymes for carbon and nitrogen metabolism.