Difference of selenium uptake and distribution in the plant and selenium form in the grains of rice with foliar spray of selenite or selenate at different stages

Foliar spray of selenium (Se) has increasingly been applied to improve Se concentrations in crops. There is a lack of systematic and in-depth study comparing the effects of foliar spray with different Se sources at different growth stages. In this study, selenite or selenate (75 g Se ha(-1)) was sprayed to the foliage of rice plants at the late tillering or full heading stage. Se concentrations in different parts of rice plants were determined to assess the effects of foliar spray with different Se sources at different growth stages on Se distribution in the plant, Se metabolism in the grains, and Se recovery efficiency in the brown rice. At the same spraying stages, total Se, organic Se, and protein Se concentrations in brown rice obtained with selenate were 2-fold those obtained with selenite. With the same Se sources, total Se, organic Se, and protein Se concentrations in brown rice treated at full heading were 2-fold higher than those treated at late tillering. The delay of spraying stage decreased the distribution ratio of Se in straw and roots, while it increased the distribution ratio of Se in grain; this trend was more evident with selenate. The proportions of organic Se and protein Se in brown rice showed no differences between selenite and selenate treatments at the same stages. The delay of spraying stage decreased the proportions of organic Se and protein Se in brown rice (still up to 80% and 44%, respectively), whereas the recovery efficiency of Se was improved in brown rice by more than 1-fold. In conclusion, appropriately delaying the spraying stage and selecting selenate as the Se source can be more efficient for producing Se-enriched rice.