Oxidative stress in Prymnesium parvum: cellular mechanisms, redox regulation, and implications for harmful algal bloom management

Prymnesium parvum is a mixotrophic haptophyte known for its harmful algal blooms (HABs), which are driven by its ability to adapt to fluctuating environmental conditions, particularly osmotic and oxidative stress. This work explores the physiological, molecular, and ecological responses of P. parvum to osmotic shifts, both hypo- and hyperosmotic—and their intersection with mechanisms of oxidative stress. Rapid adjustments in cell volume, membrane composition, and cytoskeletal structure, as well as biosynthesis of compatible solutes, allow P. parvum to tolerate a wide salinity range (0.5–30 PSU). Gene expression studies reveal up-regulation of aquaporins, ion transporters, and stress-related chaperones, orchestrated by signaling cascades involving calcium and reactive oxygen species (ROS). Although it lacks catalase and possibly conventional photorespiration, P. parvum maintains ROS homeostasis through peroxiredoxins and superoxide dismutase. Importantly, oxidative stress, salinity, and nutrient status influence prymnesin toxin production, underscoring the ecological relevance of these stress responses.