Wavelength-dependent induction of thymine dimers and growth rate reduction in the marine diatom Cyclotella sp. exposed to ultraviolet radiation

Cultures of thc marine diatom C}~clotella sp. were subjected to vanous polychromatic exposures of UVB radiation (280-320 nm), UVA radiation (320-400 nm) and photosynthetically active radiation, PAR (400-700 nm).Changes in growth rate and residual thymine dlmer content (a measure for DNA damage) were measured during prolonged exposure (6 to 7 d) to these conditions.Also, changes in medn cell size were studled as an Indication of UV radiation induced cell cycle arrest in Cyclotella sp.Growth rate reduction was strongly relrlted with residual thymine dimer content in treatments including wavelengths below 302 nm.Additionally, slgniflcant i n c r ~a s e s in mean cell size w r r e found In these cultures.This suggests that UVB-induced residual DNA damage IS followed by ccll cycle arrest and growth rate reduction in Cyclotella sp.We discuss how these results can be interpreted in relation to changes In the solar spectrum as a result of stratospheric ozone reduction.