Preliminary study on the effects of heavy metals on the growth and some antioxidant enzymes in Arthrospira platensis-M2 strain

In this study, we have analyzed superoxide dismutase (SOD), ascorbate peroxidase (APX) and glutathione reductase (GR) activities, biomass accumulation and chlorophyll-a content in the Arthrospira platensis-M2 strain grown at different concentrations of zinc (Zn), tin (Sn) and mercury (Hg). We found that there is a close relationship between chlorophyll-a content and biomass accumulation in A. platensis-M2 strain as a result of Zn, Sn and Hg exposures. Sn was found to be the most toxic heavy metal among others because of the continious inhibition of both biomass and chlorophyll-a accumulation at 500 and 1000 mu g mL(-1) concentrations after the third day of the study, while they represented continuous increases at each Zn and Hg concentration over 7 days. Lower concentrations of Zn and Sn stimulate SOD and GR activities remarkably, probably due to oxidative stress caused by heavy metal toxicity. APX activity was significantly lowered by higher concentrations of the three metals used in this study. Our results suggest that higher heavy metal concentrations inhibited SOD, APX and GR activities but biomass and chlorophylla accumulation endured in a time-dependent manner, possibly due to some different defence mechanisms, which remain to be investigated.