Assessment of oxidative stress in the planktonic diatom Thalassiosira pseudonana in response to UVA and UVB radiation

Induction of oxidative stress by UVA and UVB in the diatom Thalassiosirapseudonana was experimentally studied. Cells, pre-grown in alight-limited continuous culture, were incubated for 4 h at175 µmol m^-2s^-1photosynthetically active radiation, withoptional supplementary UVA at an unweighted dose rate of 0.70W m^-2, or 2.79 W m^-2UVA plus 0.45 W m^-2UVB (unweighted). A fluorescence-basedmeasure of photosynthetic efficiency (F_v/F_m) decreased from0.69 to 0.58 in the presence of UVB, whereas UVA caused a minordecrease of F_v/F_m. Quantitative analysis of confocal imagesshowed a minor increase of active oxygen production associatedwith supplemental UVA alone, and a 100% increase with additionalUVB. Cellular malondialdehyde, an indicator of lipid peroxidationby active oxygen, almost doubled under UVA and increased three-foldwith additional UVB. Activities of superoxide dismutase (scavengingactive oxygen) and glutathione reductase (reducing GSSG to GSH)increased in response to UVB exposure, whereas ascorbate peroxidaseactivities did not. UVB caused a minor decrease in the glutathioneratio GSH : (GSH + 0.5GSSG), which indicates a moderate oxidativestress.