Modulation of glutathione and antioxidant enzymes in Tetraselmis gracilis (Prasinophyceae) and Gracilaria tenuistipitata (Rhodophyceae) cultures under copper-induced stress

Abstract

This study is a contribution to the Thematic Project (FAPESP 01/13482-6) concerning the investigation on the cellular, biochemical and molecular mechanisms in marine algae under pollutant stress. Metal stress in most of the organisms is related to the generation of reactive oxygen species, reduction of antioxidant components, and competition between toxic and essential metals for active sites in biomolecules. Glutathione (GSH) is a multifunctional metal-chelating tripeptide that serves as a co-substrate for a range of antioxidant enzymes. In the present study we will investigate the modulation of GSH and antioxidant enzymes, including superoxide dismutase, catalase, ascorbate peroxidase, and the GSH-related enzymes, as a defence mechanism against copper-induced stress in cultures of the unicellular microalga Tetraselmis gracilis and the red macroalga Gracilaria tenuistipitata. The prasinophyta T. gracilis is of commercial interest for aquaculture due to its high nutritional value, essential for the larval phases of fish and invertebrates, whilst the rhodophyta G. tenuistipitata is an important source of agar, and therefore of economical value for industries of biotechnology, food and cosmetics. These algae are widespread, occurring in the Brazilian coast, and are relatively ease to culture. Cultures of T. gracilis and G. tenuistipitata will be incubated with copper ions at varying concentrations (EC20 e EC50) for a 24 h exposure period. The modulation of GSH and antioxidant enzymes in these cultures will be compared with that of the control-cultures, not treated with copper ions in excess. The toxic effects of copper will be assessed in terms of the extension of the peroxidation of lipids and proteins. The results will provide a better understanding on the tolerance of these algae to the environmental stress, and allow a comparison of the defence mechanisms between a unicellular organism with other presenting a more complex biological system.