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In symbioses between invertebrates and microalgae, host tissues are exposed to levels of photosynthetically produced oxygen. The biochemical consequences of symbioses been poorly investigated in Mediterranean species, but a general increase in antioxidant has been recently reported in the demosponge Petrosia ficiformis as an adaptive response the cyanobacterium Aphanocapsa feldmanni. Since Mediterranean symbioses naturally experience seasonal variations in symbiont content, light intensity and seawater temperature, the of this work was to investigate if these fluctuations modulate the prooxidant challenge to sponge. Antioxidant efficiency was characterised on a monthly basis by combining an analysis of the antioxidants (superoxide dismutase, catalase, glutathione S-transferases, glutathione reductase, peroxidases) with measurements of the total oxyradical scavenging capacity (TOSC), thus achieving a more holistic assessment of the capacity of sponge tissues to absorb different of reactive oxygen species. Symbiotic sponges showed significant seasonal changes in efficiency, with more marked variations in tissues directly exposed to photosynthetically reactive oxygen species. The greatest variations were observed during the summer, with the highest seasonal values for some defences (i. e. catalase) and the lowest for others (i. e. glutathione peroxidases). The marked increase in catalase and TOSC in summer suggests production of H2O2 in the symbioses during this period, supporting the hypothesis that seawater can significantly modulate the prooxidant challenge in Mediterranean symbioses. results suggest that species with lower antioxidant efficiency may be less tolerant of conditions oxidative damage; e. g. increases in temperature during the summer months.
Regoli et al. (Thu,) studied this question.