| Resumo: |
Plants of Azolla caroliniana were treated with different selenium concentrations (0, 1, 2, 5, 7, 10 ppm) for seven days. Selenium (Se) content in Azolla plants increased significantly with increasing Se concentrations in the culture media up to 5 ppm. This indicated that Azolla plants were a good accumulator for Se. Selenium accumulation determined changes in Azolla biomass, doubling time and relative growth rates. Treatment of Azolla plants with low concentrations of Se (1 ppm) resulted in a significant increase in biomass. This was accompanied by a reduction in hydrogen peroxide and malondialdehyde (MDA) contents; the decrease percentages were 78% and 60%, respectively at 1 ppm Se in comparison with the control. At higher Se concentrations (>5 ppm), there was a significant increase in H2O2 and MDA contents, these increases were 3.2- and 2.8-fold at 10 ppm Se in comparison to controls, respectively. Compared to that in controls, total ascorbate as well as total glutathione contents, were significantly increased. The activity of the GR enzyme was significantly increased in Azolla plants with addition of different concentrations of Se. The increase was 2.2- and 3.4-fold at 2 and 7 ppm Se, respectively. The addition of high concentrations of Se (>5 ppm) to the growth media resulted in a significant increase in the GSH-PX and APX activities in Azolla plants. Thus, addition of Se afects Azolla plants, and these effects change from benefcial to toxic, as reflected in the metabolism and growth of the plants.
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