UVB radiation modifies protein and photosynthetic pigment content,volume and ultrastructure of marine diatoms

Abstract

Three marine diatom species (Cyclotella sp., Nitzschia closterium andThalassiosira nordenskioldii) were exposed to a range of daily doses ofultraviolet B radiation (UVBR: 280-320 nm). The lowest UVBR treatments (<2000J m-2 d-1 DNA weighted biologically effective dose, normalised at 300 nm:daily BED(DNA 300 nm)) resulted in decreased division rates, volumeenlargement and elevated cellular protein and pigment content levels. Thehighest UVBR treatments (between 2000 and 3800 J m-2 d-1 daily BED(DNA300 nm)) resulted in complete growth inhibition, accompanied by only minorchanges in protein, pigments and cell volume. Recovery of cell division afterUVBR exposure was decreasingly successful with increasing UVBR dose rates.Ultrastructural examination of exposed Cyclotella cells indicated that highUVBR levels induced plasmolysis and disorientation of cell organelles. Lowerlevels (<2000 J m-2 d-1 daily BED(DNA 300 nm)) seemed to cause anincrease in volume and the amount of chloroplasts. The results support thenotion conceived earlier that UVBR causes DNA damage, an arrest in the S orG2 phase of the cell cycle, and consequently growth without cell division.