[Accumulation and Translocation of Cd in Brassica rapa Under the Influence of Selenium].

Cadmium (Cd) is a highly toxic heavy metal. Brassica rapa (pak choi) is a vastly common vegetable, which readily accumulates Cd. Given the current conditions of Cd contamination in domestic soil, it is important to reduce Cd accumulation in the edible part of pak choi. Research has shown that selenium (Se) can regulate Cd uptake by plants. Cd accumulation (three cultivars) and Cd uptake kinetics in pak choi were investigated under hydroponic conditions. Results showed that the three levels of selenite significantly reduced Cd content in the Hangzhouyoudonger shoot by 50%, while the levels in Suzhouqinggen and Shanghaiqing shoots were not significantly decreased with elevated levels of selenite. Selenite reduces the Cd translocation factors, and higher levels had more obvious effects; 50 µmol·L-1 of selenite significantly decreased the factors by 50% in Hangzhouyoudonger and Suzhouqinggen shoots. Selenite also increased iron (Fe) and manganese (Mn) contents in pak choi, especially in the Hangzhouyoudonger shoot, where 50 µmol·L-1 increased the Fe content by approximately 50%. In the uptake kinetics of Cd, both selenite and selenate significantly increased Cd uptake rates and Vmax by over 100%. Therefore, Se could reduce Cd accumulation in pak choi. This also depended on the tested cultivar. Therefore, reduction effects of Se on the Cd content mainly stemmed from the alteration of Cd translocation in pak choi instead of the uptake competition between Cd and Se.

Selenium Uptake and Biotransformation in Brassica rapa Supplied with Selenite and Selenate: A Hydroponic Work with HPLC Speciation and RNA-Sequencing.

Vegetables are an ideal source of human Se intake; it is important to understand selenium (Se) speciation in plants due to the distinct biological functions of selenocompounds. In this hydroponic study, the accumulation and assimilation of selenite and selenate in pak choi (Brassica rapa), a vastly consumed vegetable, were investigated at 1-168 h with HPLC speciation and RNA-sequencing. The results showed that the Se content in shoots and Se translocation factors with selenate addition were at least 10.81 and 11.62 times, respectively, higher than those with selenite addition. Selenite and selenate up-regulated the expression of SULT1;1 and PHT1;2 in roots by over 240% and 400%, respectively. Selenite addition always led to higher proportions of seleno-amino acids, while SeO42- was dominant under selenate addition (>49% of all Se species in shoots). However, in roots, SeO42- proportions declined substantially by 51% with a significant increase of selenomethionine proportions (63%) from 1 to 168 h. Moreover, with enhanced transcript of methionine gamma-lyase (60% of up-regulation compared to the control) plus high levels of methylselenium in shoots (approximately 70% of all Se species), almost 40% of Se was lost during the exposure under the selenite treatment. This work provides evidence that pak choi can rapidly transform selenite to methylselenium, and it is promising to use the plant for Se biofortification.