Stress regulation of photosynthetic system of Phaeocystis globosa and their hemolytic activity.

Blooms of Phaeocystis globosa have been reported accountable for massive fish mortality worldwide. The toxigenic mechanisms of P. globosa, however, remain largely unclear due to the multiple structures and/or synergistic or antagonistic effects of hemolytic compounds. External stressors could lead to the regulation of photoprotective or antioxidative defense system, as well as the potential hemolytic activity. Therefore, the light-induced photosynthetic system, including the accessory photosynthetic growth, the relative electron transfer rate (ETR), photosynthetic efficiency (Fv/Fm), quantum yield of photosystem II (Yield), together with the hemolytic activity of P. globosa were investigated under variable environmental conditions in the present study. Results confirmed that hemolytic activity of P. globosa was initiated by the light, but inhibited by low temperature (16 °C), high light intensity (>100 µmol/(m2·s)), and iron-limited conditions. Interestingly, the hemolytic activity was not impacted by photosynthetic electron inhibitors (Diuron, atrazine, paraquat, and dibromothymoquinone), which significantly inhibited the photosynthetic activity of P. globosa. The correlated response of hemolytic and photosynthetic activity of P. globosa under those environmental factors suggested that the hemolytic compounds of P. globosa would be involved in the photosynthetic process but not in the electron transfer chain of P. globosa. [ABSTRACT FROM AUTHOR]