In the present study, we describe the molecular and functional characterization of two Cu,Zn superoxide dismutase (SOD) genes, named tt-sod1a and tt-sod1b from Tetrahymena thermophila, a free-living ciliated protozoan widely used as model organism in biological research. The cDNAs and the putative amino acid sequences were compared with Cu,Zn SODs from other Alveolata. The primary sequences of T. thermophila Cu,Zn SODs are unusually long if compared to orthologous proteins, but the catalytically important residues are almost fully conserved. Both phylogenetic and preliminary homology modeling analyses provide some indications about the evolutionary relationships between the Cu,Zn SODs of Tetrahymena and the Alveolata orthologous enzymes. Copper-dependent regulation of Cu,Zn SODs expression was investigated by measuring mRNA accumulation and enzyme activity in response to chronic exposure to non-toxic doses of the metal. Our in silico analyses of the tt-sod1a and tt-sod1b promoter regions revealed putative consensus sequences similar to half Antioxidant Responsive Elements (hARE), suggesting that the transcription of these genes directly depends on ROS formation. These data emphasize the importance of complex metal regulation of tt-sod1a and tt-sod1b activation, as components of an efficient detoxification pathway allowing the survival of T. thermophila in continued, elevated presence of metals in the environment.

Ulva rigida (C. Agardht) was collected from the Palude della Rosa (lagoon of Venice), a particular area characterized by a salinity gradient, from December 1991 to June 1993. Metal contents (Al, Mn, Fe, Cu, Zn, Cr, Co, Ni, Cd, and Pb) were determined by atomic absorption spectrophotometry and statistically analysed for differences between months and sampling sites. The mean seasonal variability is very significant (p < 0.001) for all studied metals. Seasonal trends are comparable for groups of metals according to possible functional similarities. A significant positive correlation was calculated for the pairs Fe-Al and Fe-Pb. Mechanisms regulating metal uptake are discussed, particularly the role of Fe and its linear relationship with Al. Metal concentrations in relation to salinity also were studied. Larger amounts of Fe, Zn, and Cd accumulated in correspondence of lower salinity, may be owing to both higher metal activity and burden of bioavailable metals in freshwater flowing into the Palude. Calculation of concentration factor (CF) indicates that U. rigida specifically accumulates Fe. CF linearly correlates with dissolved metal concentrations, suggesting that U. rigida is a good bioindicator of metal bioavailability, although seasonal active accumulation occurs in some cases (Mn). Metal concentrations determined in this macroalga support the conclusion that the studied area is rich in bioavailable Fe and poor in toxic metals. In any case, a great affinity for Al in U. rigida may be proposed.

Ulva rigida (C. Agardht) was collected from the Palude della Rosa (lagoon of Venice), a particular area characterized by a salinity gradient, from December 1991 to June 1993. Metal contents (Al, Mn, Fe, Cu, Zn, Cr, Co, Ni, Cd, and Pb) were determined by atomic absorption spectrophotometry and statistically analysed for differences between months and sampling sites. The mean seasonal variability is very significant (p < 0.001) for all studied metals. Seasonal trends are comparable for groups of metals according to possible functional similarities. A significant positive correlation was calculated for the pairs Fe-Al and Fe-Pb. Mechanisms regulating metal uptake are discussed, particularly the role of Fe and its linear relationship with Al. Metal concentrations in relation to salinity also were studied. Larger amounts of Fe, Zn, and Cd accumulated in correspondence of lower salinity, may be owing to both higher metal activity and burden of bioavailable metals in freshwater flowing into the Palude. Calculation of concentration factor (CF) indicates that U. rigida specifically accumulates Fe. CF linearly correlates with dissolved metal concentrations, suggesting that U. rigida is a good bioindicator of metal bioavailability, although seasonal active accumulation occurs in some cases (Mn). Metal concentrations determined in this macroalga support the conclusion that the studied area is rich in bioavailable Fe and poor in toxic metals. In any case, a great affinity for Al in U. rigida may be proposed.

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