Selenium reduces cadmium accumulation in seed by increasing cadmium retention in root of oilseed rape (Brassica napus L.)

Cadmium (Cd) accumulation in edible part of crop threatens human health. The beneficial effects of selenium (Se) have been established in improving plant growth and reducing Cd accumulation in plant under Cd stress. This study investigated the effect of Se in reducing Cd concentration in seed, and revealed the underlying regulating mechanisms in root of rape. Results showed that when plants were grown in Cd contaminated soil, the application of exogenous Se significantly reduced Cd concentration in seed. Under 5 mu mol L-1 Cd stress, the photosynthesis and photosynthetic pigment contents in leaf tissue were improved with the addition of Se; Se reduced Cd concentration in root, while root morphology showed little variation by comparison with Cd treated alone. Further studies on root revealed that Se addition increased the concentration of Cd with inactive forms. Except that, Se increased the contents of pectin and hemicellulose 2, which was consistent with the elevated Cd concentration in root cell walls. Findings in this study may indicate that with the application of Se, the proportion of less mobile Cd-complex is enhanced, and the Cd binding to root cell wall increases along with the elevated contents of pectin and hemicellulose 2; all of these contribute to the reduction of Cd uptake in root and therefore transportation to stem, pod, and finally seed.