Responses of marine macroalgae to hydrogen-peroxide stress

In this study, we determined the antioxidative potential of 15 marine macroalgae by measuring the photosynthetic efficiency under artificial oxidative stress after a 30-min exposure to a series of ascending H2O2 concentrations. Species exhibiting high maximum quantum yields (Fv/Fm values) were regarded as not susceptible towards H2O2 stress. In addition to the short-term stress experiments, the antioxidative defense systems (enzymatic and non-enzymatic) of selected algal species under longer exposure times to H2O2 were investigated. Species with striking photosynthetic activity under H2O2 stress were Chaetomorpha melagonium (Chlorophyta), showing 40% reduced Fv/Fm as compared to the control after 8 days of exposure to 20 mM H2O2. In Fucus distichus (Phaeophyta) Fv/Fm decreased to 50% of the control under the same exposure conditions. Polysiphonia arctica (Rhodophyta) exhibited highest Fv/Fm values with a reduction of only 25%, therefore possessing the highest antioxidative potential of the investigated species. In P. arctica the activities of the antioxidative enzymes superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR), as well as the pool size of the antioxidant ascorbic acid were investigated. When exposed to different H2O2 concentrations (0–2 mM) over 6 days, the intrinsic activities of SOD and GR were stimulated. In a kinetic study over 8 days, the activity of antioxidative enzymes APX and CAT as well as ascorbic acid content were recorded. APX activity was much higher in H2O2-treated thalli at the end of the experiment than in the control, also CAT activity increased significantly with increasing H2O2 stress. In parallel, ascorbic acid content was reduced under high H2O2 concentrations. Furthermore, by using GC–MS techniques in P. arctica bromophenolic compounds with antioxidative properties were identified. This study shows that the measurement of the in vivo fluorescence of photosystem II is a suitable tool to determine the effect of oxidative stress on macroalgae. From these studies it is obvious that different algal species have varying strategies against oxidative stress which correlate with zonation on the shore.