Physiological Mechanism of Exogenous Selenium in Alleviating Mercury Stress on Pakchoi (Brassica campestris L.)

The objective of this study was to explain the physiological mechanisms through which Na2SeO3 mitigates the growth and developmental inhibition of pakchoi under HgCl2 stress. The results showed that treatment with HgCl2 (40 mg L-1) led to reduced biomass, dwarfing, root shortening, and root tip necrosis in pakchoi. Compared to control (CK), the activities of superoxide dismutase (SOD) and peroxidase (POD) in Hg treatment increased, and the content of malondialdehyde (MDA) also dramatically increased, which negatively impacted the growth of pakchoi. Low concentrations of Na2SeO3 (0.2 mg L-1) significantly increased the content of soluble sugars compared with control, while chlorophyll, soluble proteins, free amino acids, and vitamin C had no significant changes. The results of the mixed treatments with HgCl2 and Na2SeO3 suggested that selenium may be able to reduce the toxicity of mercury in pakchoi. The biomass, plant height, root length, chlorophyll content, soluble protein, other physiological indicators, and proline showed significant increases compared with the HgCl2 treatment. Additionally, the MDA content and mercury accumulation in pakchoi decreased. Our results revealed the antagonistic effects of selenium and mercury in pakchoi. Thus, a theoretical basis for studying pakchoi's mercuryexcreted and selenium-rich cultivation technology was provided.