UV-B radiation increases cell permeability and damages nitrogen incorporation mechanisms in Nannochloropsis gaditana

Abstract.

This study shows the response of Nannochloropsis gaditana, a marine nannoplanktonic species, exposed to UV radiation for 7 days. PAR, UV-A and UV-B ratios used were within the range likely to be observed in nature, a photoperiod of 12L:12D was maintained, and light irradiances were modified daily to promote cell acclimation. Growth, pigment content, internal nitrogen and carbon content, and photochemical efficiency using PAM fluorometry were assessed in nutrient replete cultures. Cell size, autofluorescence and cell permeability were analysed by flow cytometry. Results showed a cessation of growth after day 3 and a progressive decrease was observed in F_v/F_m values in cultures exposed to UV-B (plus UV-A and PAR). Flow cytometry analysis also demonstrated an increase in membrane permeability caused by UV-B damage. Cells that showed an increase in membrane permeability also exhibited a proportional decrease in cellular nitrogen content. The results support the conclusion that UV-B radiation can affect N. gaditana nitrogen incorporation mechanisms by direct damage or indirectly by damage to membrane structure and to the photosynthetic apparatus with resulting effects on energy and reductant demand. In contrast, the presence of UV-A radiation was beneficial to cells exposed to PAR plus UV-A when compared to those exposed to only-PAR from day 4. This response resulted in cells with a higher nitrogen content and without changes in membrane permeability.