Detoxification Effect of Selenium: Alleviating the Inhibition of Cadmium Stress on the Growth of Rape (Brassica napus L.) by Regulating Photosynthetic Pigments, Metal Complexation Reaction, and Antioxidant System

Cadmium is considered a highly toxic metallic element that does not have any beneficial biological functions for humans or plants. It has been reported that the antagonism of selenium to heavy metal stress has been observed in a variety of plants, and appropriate selenium could alleviate heavy-metal-induced oxidative damage and reduce the accumulation of heavy metals in plants. Changes in physiological characteristics, root tip cells, cadmium concentration, and accumulation of rape under cadmium stress were investigated in this study through pot experiment. Results showed that selenium could alleviate the inhibitory effect of cadmium on the growth of rape seedlings. The concentration and accumulation of cadmium were decreased after the selenium application in rape seeds, ranging from 19.93 to 22.97% and 27.96 to 43.88%, respectively, and the decrease in photosynthetic pigment content induced by cadmium was significantly improved. The results of transmission electron microscopy showed that exogenous selenium and cadmium had metal complexation reaction and formed black precipitation, which may be related to the detoxification effect of selenium on cadmium. More critically, with the addition of selenium, the plasma membrane damage and free radical accumulation in root tips induced by cadmium stress were gradually alleviated in the histochemical staining experiment of rape root tips. These results may provide evidence for exploring effective measures to reduce cadmium accumulation in rape under cadmium-contaminated areas.