Reactive oxygen species-mediated caspase-3 pathway involved in cell apoptosis of Karenia mikimotoi induced by linoleic acid

Linoleic acid (LA) secreted by macroalgae has been shown to inhibit harmful algal blooming Karenia mikimotoi. In this study, we investigated the effects of LA on cell proliferation and apoptosis of K. mikimotoi. The results indicated that LA ( > 500 mu g/L) could significantly inhibit the algal proliferation, with the cell cycle blocked at the G(2 )phase and a clear decrease of photosynthetic pigments. Intracellular reactive oxygen species (ROS) level, malondialdehyde (MDA) content and the activities of antioxidant enzymes (superoxide dismutase (SOD) and catalase (CAT)) were obviously elevated, indicating that LA induced oxidative stress of K. mikimotoi. Several indicators for cell apoptosis, including DNA degradation, increased caspase-3 protease activity and phosphati dylserine (PTS) externalization, were observed in K. mikimotoi treated by LA. Addition of the ROS scavenger N-acetyl-L-cysteine (NAC) decreased caspase-3 activity, and reduced cell apoptosis. Caspase-3 inhibitor also decreased cell apoptosis rate. Summarily, the results suggest that LA induced ROS overproduction, which further stimulated caspase-3, and then induced cell apoptosis of K. mikimotoi.