Nitrate Reductase-Dependent Nitric Oxide Production Is Involved in Microcystin-LR-Induced Oxidative Stress in Brassica rapa

Abstract

Histochemical and biochemical approaches were used to investigate the phytotoxicity induced by microcystin-LR (MC-LR) in the shoots of Brassica rapa seedlings. MC-LR exposure was able to induce oxidative stress by triggering the over-generation of reactive oxygen species (ROS) including superoxide anion radical (O2 ● � ) and hydrogen peroxide (H2O2 )i n the shoots of B. rapa. MC-LR exposure led to the significant increase in the concentration of endoge- nous nitric oxide (NO) in B. rapa .H owever, such increase was completely suppressed by the treatment with nitrate reductase (NR) inhibitor NaN3, while L- NMMA, a NO synthase (NOS) inhibitor, had only slight effect on the content of endogenous NO in MC-LR-treated plant. These data suggested that NR- dependent pathway was the main source for endoge- nous NO generation under MC-LR stress. Afterwards, treatment with NaN3 reduced the ROS generation, lipid peroxidation, and loss of membrane integrity in MC-LR-treated plant. MC-LR stress induced the in- crease in the expression of superoxide dismutase, ascorbate peroxidase, and catalase. However, such an effect could be reversed by the treatment with NaN3. These results indicate that NR-dependent NO produc- tion mediates MC-LR-induced oxidative stress by trig- gering the over-generation of ROS in B. rapa.