Insights into uptake, accumulation, and subcellular distribution of selenium among eight wheat (Triticum aestivum L.) cultivars supplied with selenite and selenate.

Selenium (Se)-enriched wheat can be improved by altering Se sources and selecting wheat cultivars. Such improvement can affect subcellular distribution and speciation of Se in wheat. Thus, a pot experiment was conducted to investigate Se uptake and distribution when Se was applied as selenite or selenate at low and high rates (1 and 10 mg kg-1, respectively). Moreover, Se's impact on the grain and biomass yield of eight wheat cultivars was also investigated. The subcellular distribution and speciation of Se were also explored to elucidate Se metabolism and micro-distribution pattern in wheat. Results showed that biomass and grain yield were decreased with the application of both selenite and selenate in almost all the cultivars, regardless of the Se rate. Application high Se rate resulted in a significant (p < 0.05) decrease in grain yield and biomass compared with low rate of Se. Compared with the low rate of selenite application, the grain and the biomass yield of ZM-9023 significantly (p < 0.05) increased by about 15% for low rate of selenate application. In addition, both selenite and selenate treatment increased the uptake of Se in each part of wheat, compared with the control. Selenium was mostly accumulated in the grain and root of wheat under selenite treatment, while more Se accumulation was found in leaves and straw for selenate application. Further investigation on the subcellular distribution of Se showed that the proportion of Se in soluble fraction was significantly (p < 0.05) higher in wheat leaves than that in organelle fraction and cell walls (46%-66%). Meanwhile, Se6+ was the main species found in soluble fraction, whereas SeMet and MeSeCys were the species predominantly stored in organelle fraction. In conclusion, wheat cultivar ZM-9023 is the most Se-rich potential cultivar, and the isolation of Se in the soluble fraction plays an important role in Se tolerance and accumulation.

[Transformation and influences of copper and selenium fractions on heavy metals bioavailability in co-contaminated soil].

Pot experiments and laboratory analysis methods were used to investigate the form transformation of additional copper and selenium and their bioavailability for pakchoi (Brassica chinensis) in co-contaminated soil. The results showed that Cu mainly existed in residual bound form, while selenium was present mainly in organic bound and residual form in the uncontaminated soil. In the contaminated soil, copper was mainly bounded to hydrated oxides of iron and manganese, while Se was in exchangeable and carbonate forms. After one month of growing season, Cu tended to transfer into organic bound fractions, while Se tended to bind to hydrated oxides of iron and manganese. The I(R) value of Cu decreased with increasing copper and selenium concentrations, while the I(R) value of Se decreased with increasing Se concentration and had nothing to do with the concentration of exogenous Cu for both before planting and after harvesting of pakchoi. The parameters estimated by S curve fitting indicated that suitable amount of Se (< or = 10 mg x kg(-1)) could promote the Cu uptake by pakchoi, and certain amount of Cu (< or = 400 mg x kg(-1)) could promote Se absorption by pakchoi. Both the I(R), values for Cu and Se had similar trends as the Cu, Se concentrations in pakchoi, which meant that the I(R) value could be used to evaluate the bioavailability of heavy metals in soil. Partial correlation analysis showed that Cu and Se in exchangeable and organic bound forms in soil had better bioavailability for pakchoi. Therefore, the I(R) value of elements in soils and the change of elements before planting and after harvesting of pakchoi can be used as indicators for evaluating the bioavailability of heavy metals.