Toxicity assessment of arsenate and arsenite on growth, chlorophyll a fluorescence and antioxidant machinery in Nostoc muscorum.

The present study deals with impact of varied doses of arsenite (As; 50, 100 and 150 µM) and arsenate (As; 50, 100 and 150 mM) on growth, photosynthetic pigments, photochemistry of photosystem II, oxidative biomarkers, (O¯, HO and MDA equivalents contents) and activity of antioxidant enzymes in diazotrophic cyanobacterium Nostoc muscorum after 48 and 96 h of the treatments. The reduction in growth, pigment contents (Chl a, Phy and Car) and PS II photochemistry was found to increase with enhanced accumulation of test metal in cells, and the damaging effect on photosynthetic pigments showed the order (Phy > chl a> Car). The negative effect on PS II photochemistry was due to significant decrease in the value of JIP kinetics ϕP, F/F, ϕE,Ψ and PI except F/F and significant rise in values of energy flux parameters such as ABS/RC, TR/RC, ET/RC and DI/RC. Both the species of arsenic caused significant rise in oxidative biomarkers as evident by in vitro and in vivo analysis of (O¯, HO and MDA equivalents contents) despite of appreciable rise in the activity antioxidative enzymes such as SOD, POD, CAT and GST. The study concludes that in among both forms of arsenic, arsenite effect was more dominant on growth, photosynthetic pigments; oxidative stress biomarkers as evident by weak induction of anti-oxidative defense system to overcome the stress as compared to arsenate.