Low salinity causes oxidative stress and modulates specific antioxidant gene expression in the toxic dinoflagellate Alexandrium pacificum

Salinity is an important factor in the physiological regulation of algae; however, its influence on the genomic responses in toxic dinoflagellates is insufficiently understood. In the present study, we evaluated the effect of salinity stress on the physiology, photosynthesis, and molecular responses of the toxic dinoflagellate Alexandrium pacificum (group IV). When exposed cells to different salinities of 20-40 psu, we detected the lowest cell density (3.25 x 10(3) cells mL(-1)) and highest cell size (30.6 mu m) at 20 psu. Photosynthesis efficiency considerably decreased at 20 and 40 psu compared to the control (33 psu). Quantitative real-time polymerase chain reaction revealed that psbA, psbD, and atpC expression levels were significantly downregulated under conditions of salinity stress for 72 h. In contrast, the expression levels of antioxidant genes MnSOD and GPx were greatly upregulated at 20 psu (13.2- and 15.2-fold changes at 6 h; 8.8- and 8.3-fold changes at 24 h, respectively). The expression levels of other antioxidant genes, CuZnSOD, GST, and APx, increased steadily over time under salinity stress. Such conditions increased the relative levels of reactive oxygen species by 2.2-fold in 6 h and 2.4-fold in 24 h at 20 psu. These results suggest that low salinity may cause cellular oxidative stress, leading to a decrease in photosynthesis and affecting specific antioxidant systems in toxic dinoflagellates.

Automated summary

This study evaluated the effect of low salinity on the toxic dinoflagellate Alexandrium pacificum. The results showed that low salinity led to a decrease in cell density, an increase in cell size, and a decrease in photosynthesis efficiency. Additionally, low salinity induced cellular oxidative stress and affected the antioxidant systems in the toxic dinoflagellates.