Temporal mismatch between induction of superoxide dismutase and ascorbate peroxidase correlates with high H2O2 concentration in seawater from clofibrate-treated red algae Kappaphycus alvarezii

Algal cells have developed different strategies to cope with the common environmentally promoted generation of H2O2, which include induction of catalase (CAT) and ascorbate peroxidase (APX), massive H2O2 release in seawater, and synthesis of volatile halocarbons by specific peroxidases. The antioxidant adaptability of the economically important carrageenophyte Kappaphycus alvarezii (Doty) Doty (Gigartinales: Rhodophyta) was tested here against exposure to clofibrate (CFB), a known promoter of peroxisomal β-oxidation in mammals and plants. Possibly as a consequence of CFB-induced H2O2 peroxisomal production, the maximum concentration of H2O2 in the seawater of red algae cultures was found to occur (120 ± 17 min) after the addition of CFB, which was followed by a significant decrease in the photosynthetic activity of PSII after 24 h. Interestingly, 4 h after the addition of CFB, the total SOD activity was about 2.5-fold higher than in the control, whereas no significant changes were observed in lipoperoxidation levels (TBARS) or in CAT and APX activities. The two H2O2-scavenging enzymes were only induced later (after 72 h), whereupon CAT showed a dose-dependent response with increasing concentrations of CFB. A more pronounced increase of TBARS concentration than in the controls was evidenced when a 50 μM Fe2+/3+ solution (3:2 ratio) was added to CFB-treated cultures, suggesting that the combination of exacerbated H2O2 levels in the seawater—in this work, caused by CFB exposure—and Fenton-reaction catalyst (ferric/ferrous ions), imposes harsh oxidative conditions on algal cultures. The bulk of data suggests that K. alvarezii possesses little ability to promptly induce CAT and APX compared to the immediately responsive antioxidant enzyme SOD and, to avoid harmful accumulation of H2O2, the red alga presumably releases H2O2 into the surrounding medium as an alternative mechanism.