Ultraviolet irradiation induced oxidative stress and response of antioxidant system in an intertidal macroalgae Corallina officinalis L.

The response of the antioxidant defense system of an intertidal macroalgae Corallina officinalis L.to different dosages of UV-B irradiation was investigated.Results showed that superoxide dimutase （SOD） and peroxidase （POX） increased and then maintained at a relatively stable level when subjected to UV-B irradiation.Catalase （CAT） activity under medium dosage of UV-B irradiation （Muv） and high dosage of UV-B irradiation （Huv） treatments were significantly decreased.Ascorbate peroxidase （APX） activity first remained unaltered and then increased in Huv treatment.In addition,the assay on isozymes was carried out using non-denaturing polyacrylamide gel electrophoresis （PAGE）.The activities of some SOD isoforms were altered by UV-B.Two new bands （POX V and POX VII） appeared upon exposure to all three UV-B dosages.CAT III activity was increased by low dosage of UV-B irradiation （Luv）,whereas CAT III and CAT IV disappeared when the alga was exposed to Muv and Huv.Two bands of APX （APX VI and APX VII） were increased and a new band （APX X） was observed under Huv exposure.H 2 O 2 and thiobarbituric acid reacting substance （TBARS） increased under Muv and Huv treatments.Overall,UV-B protection mechanisms are partly inducible and to a certain extent sufficient to prevent the accumulation of damage in C.officinalis.

UV-B irradiation and allelopathy by Sargassum thunbergii affects the activities of antioxidant enzymes and their isoenzymes in Corallina pilulifera

Intertidal macroalgae can cope with the dual effects of UV-B irradiation and allelopathy.To study the impacts of the two stressors,we co-cultured Corallina pilulifera with Sargassum thunbergii in 1:1 and 1:10 ratios under different doses of UV-B radiation.The response of the antioxidant defense system,focusing on activities of superoxide dismutase(SOD),ascorbate peroxidase(APX),peroxidase(POX)and glutathione reductase(GR),was monitored.In addition,isoenzyme patterns were analyzed using nondenaturing poly acry lamide gel electrophoresis.The results show that the activities of SOD,APX,and GR were all significantly affected by both UV-B radiation and allelopathy,and the effect of their interaction was significant.However,POX activity was only influenced by UV-B radiation.The enzymatic assay revealed four distinct bands of SOD.The SODⅢband weakened significantly when the co-cultures were exposed to extremely high dosage of UV-B irradiation under both co-culturing ratios of 1:1 and 1:10.When the coculturing ratio was 1:10,both POXⅡand APXⅡenzy me activities increased with different UV-B doses.GR activity was at its greatest when the co-culture ratio was 1:10 and exposure was to the higher UV-B doses.The activities of GRⅢand GRⅣwere elevated under all UV treatments whereas the activities of GRI and GRII were reduced under the lower UV-B treatments but were elevated under the higher UV-B treatments.However,lipid peroxidation,as indicated by the thiobarbituric acid-reacting substance(TBARS)assay,increased significantly under the dual stressors.Our data sugge st that allelopathy and UV-B radiation stre ss can each affect the antioxidant enzyme activities of C.pilulifera.Critically,the adverse effects of UV-B on C.pilulifera were intensified by the compounding effects of allelopathy.