Selenium invoked antioxidant defense system in Azolla caroliniana plant

Plants of Azolla caroliniana were treated with differentselenium concentrations (0, 1, 2, 5, 7, 10 ppm) for seven days.Selenium (Se) content in Azolla plants increased significantly withincreasing Se concentrations in the culture media up to 5 ppm. Thisindicated that Azolla plants were a good accumulator for Se. Seleniumaccumulation determined changes in Azolla biomass, doublingtime and relative growth rates. Treatment of Azolla plants with lowconcentrations of Se (1 ppm) resulted in a significant increase in biomass.This was accompanied by a reduction in hydrogen peroxide andmalondialdehyde (MDA) contents; the decrease percentages were78% and 60%, respectively at 1 ppm Se in comparison with the control.At higher Se concentrations (>5 ppm), there was a significantincrease in H2O2 and MDA contents, these increases were 3.2- and2.8-fold at 10 ppm Se in comparison to controls, respectively. Comparedto that in controls, total ascorbate as well as total glutathionecontents, were significantly increased. The activity of the GR enzymewas significantly increased in Azolla plants with addition of differentconcentrations of Se. The increase was 2.2- and 3.4-fold at 2 and7 ppm Se, respectively. The addition of high concentrations of Se(>5 ppm) to the growth media resulted in a significant increase inthe GSH-PX and APX activities in Azolla plants. Thus, addition ofSe affects Azolla plants, and these effects change from beneficial totoxic, as reflected in the metabolism and growth of the plants.