Effects of silver(I) toxicity on microstructure, biochemical activities, and genic material of Lemna minor L. with special reference to application of bioindicator.

In this research, several biochemical variations in plant of Lemna minor L. were investigated to reflect Ag(+) toxicity. Lemna minor L. changed colorless AgNO3 to colloidal brown at doses equal to and greater than 1 mg L(-1). Optical and fluorescence microscopy revealed the presence of bright spots in roots of tested plant related to Ag/Ag2O-NPs. Photosynthetic pigment contents of Lemna minor L. declined upon exposure to Ag(+) with an evidently higher decrease in chlorophyll a than in chlorophyll b. Similarly, Ag(+) treatment caused an evident reduction in the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT). The reduction in antioxidase activity was significantly higher in POD than in SOD and CAT. Ag(+) treatment resulted in a significant increment in the level of malondialdehyde (MDA) content as the judging criteria of cellular injury which showed sign of dose-related. The alterations occurred in RAPD profiles of treated samples following Ag(+) toxicity containing loss of normal bands, appearance of new bands, and variation in band intensities compared with the normal plants. In addition, morphological character and biomass of Lemna minor L. subjected to increasing Ag(+) concentrations were evaluated to reveal Ag(+) toxicity. Our study demonstrated that Lemna minor L. have a high sensitivity to indicate fluctuation of water quality. It would be beneficial that modulating the genotype of Lemna minor L. to bear high proportion of contaminates.