Melatonin mediates selenium-induced tolerance to cadmium stress in tomato plants.

Both selenium (Se) and melatonin reduce cadmium (Cd) uptake and mitigate Cd toxicity in plants. However, the relationship between Se and melatonin in Cd detoxification remains unclear. In this study, we investigated the influence of three forms of Se (selenocysteine, sodium selenite, and sodium selenate) on the biosynthesis of melatonin and the tolerance against Cd in tomato plants. Pretreatment with different forms of Se significantly induced the biosynthesis of melatonin and its precursors (tryptophan, tryptamine, and serotonin); selenocysteine had the most marked effect on melatonin biosynthesis. Furthermore, Se and melatonin supplements significantly increased plant Cd tolerance as evidenced by decreased growth inhibition, photoinhibition, and electrolyte leakage (EL). Se-induced Cd tolerance was compromised in melatonin-deficient plants following tryptophan decarboxylase (TDC) gene silencing. Se treatment increased the levels of glutathione (GSH) and phytochelatins (PCs), as well as the expression of GSH and PC biosynthetic genes in nonsilenced plants, but the effects of Se were compromised in TDC-silenced plants under Cd stress. In addition, Se and melatonin supplements reduced Cd content in leaves of nonsilenced plants, but Se-induced reduction in Cd content was compromised in leaves of TDC-silenced plants. Taken together, our results indicate that melatonin is involved in Se-induced Cd tolerance via the regulation of Cd detoxification.

[Quantitative partitioning of soil selenium in the selenium-rich area of Northern Zhejiang Plain].

To clarify the contribution of different component of selenium is the basis for evaluation of the sustainable development and utilization of selenium-rich soil. Xiuzhou district, where the soil is rich in selenium, was chosen as the study area, and its soil selenium content was qualitatively separated as the natural background component and the exogenous component through cross-validation of integrated geo-analysis and multivariate statistics. Subsequently, the contribution rate of the different component of the selenium content was separated quantitatively using frequency distribution functions. The results showed that the natural background component accounted for 90% in the soil selenium content and the exogenous component accounted for 10%, which indicated that the land sources rich in selenium in Xiuzhou district has the potential for sustainable development and utilization.