INFLUENCE OF ULTRAVIOLET RADIATION ON THE EXPRESSION OF PROLIFERATING CELL NUCLEAR ANTIGEN AND DNA POLYMERASE α IN SKELETONEMA COSTATUM (BACILLARIOPHYCEAE)

To evaluate the effects of UV radiation on the expression of DNA replication-related genes in phytoplankton, the mRNA levels of DNA polymerase alpha and proliferating cell nuclear antigen (PCNA) in a marine diatom, Skeletonema costatum (Greville) Cleve, were studied using the methods of real-time quantitative PCR. Treating the algal cultures with UVC radiation for 15 min caused severe mortality during the 24-h period after treatment. A significant amount of thymine dimers was detected in the treated cultures, and the mRNA levels of DNA polymerase alpha and PCNA increased by as much as 140 and 23 pmol.(g total RNA) super(-1), respectively, compared with the control experiments. In contrast, massive cell deaths did not occur in cultures receiving UVA/B radiation, and the formation of thymine dimers was inconspicuous. Also, UVA/B did not enhance the expression levels of DNA polymerase alpha or PCNA. Based on the calculation of biologically effective UV doses, daily exposure to sunlight may increase the expression of DNA polymerase alpha or PCNA genes in S. costatum by 12% at sea surface. This level of increase does not seriously affect the value of using these genes as growth indicators, but caution is needed in the extrapolation of this conclusion to all phytoplankton species.