Enzymatic defences against photooxidative stress induced by ultraviolet radiation in Arctic marine macroalgae

Abstract.

The activities of the antioxidant enzymes superoxide dismutase (SOD), glutathione reductase (GR), ascorbate peroxidase (APX) and catalase (CAT), as well as the content of the antioxidant compound ascorbic acid, were determined in five green, seven red and ten brown macroalgal species from the Kongsfjord (Spitsbergen, Svalbard, Norway). In general, higher antioxidant enzyme activities and a higher content of ascorbic acid were measured in green algae in comparison to red and brown algae. Species from the eulittoral and upper sublittoral (Acrosiphonia penicilliformis, Monostroma arcticum, Chaetomorpha linum, Chaetomorpha melagonium, Devaleraea ramentacea, Palmaria palmata) showed higher antioxidant enzyme activities compared to species from the lower sublittoral, indicating a more efficient biochemical protection in algae exposed to higher stress conditions in the field. The activity of GR was stimulated by artificial ultraviolet radiation in the green alga M. arcticum, and in the red algae Coccotylus truncatus and Phycodrys rubens after 84 h under continuous exposure. GR activity was even higher when the UV exposure was followed by incubation in darkness for 24 h, indicating a higher elimination rate of toxic oxygen radicals under these conditions. D. ramentacea, P. palmata and A. penicilliformis did not show any significant effect of UV radiation on CAT, APX and SOD activities after 8 days of culture under laboratory conditions. However, a significant reduction in activities of GR and SOD was observed in A. penicilliformis when solar UV radiation was cut off by selective filter foils in the field, indicating a lower oxidative stress in the absence of UV radiation. Overall, the ecological success of macroalgae in the eulittoral and upper sublittoral is supported by an enhanced oxygen-reactive scavenging system, allowing fast acclimation to the changes in environmental radiation conditions.