Combined foliar application of zinc sulphate and selenite affects the magnitude of selenium biofortification in wheat (Triticum aestivum L.)

Combined foliar application of zinc sulphate (ZnSO4) and selenium (Se) has been practiced in wheat biofortification. However, it remains elusive that whether the combined application affects Zn and Se distribution to grain, the efficacy of biofortification and bioavailability in wheat, due to the accompanying sulphate sources. Selenite and ZnSO4 were applied either alone or simultaneously to foliage of wheat in field, and their impacts on Zn and Se partitioning in plants, enrichment and bioavailability in whole grain, bran and flour, as well as amino acid profile in flour, were closely investigated. Grain yield was not influenced by any of the foliar Zn and Se applications. Grain Zn and Se concentrations reached 58.3-77.9 and 0.30-0.74 mg kg(-1) in Zn- and Se-sprayed plants, respectively, and the estimated daily-absorbed Zn by a reference adult from grain and flour were enhanced by 1.2- to 2.4-fold than the control, as well as 16.8-fold increase on average for daily Se intake. Combined Zn and Se application led to a 32%-37% reduction in Se concentrations and daily Se intake of whole grain and flour in one of the two seasons when compared with the foliar Se spray alone, which was partly associated with the reduced Se distribution to grains. Alternatively, similar responsive patterns of methionine and cysteine with grain and flour Se concentrations further suggested that zinc sulphate and selenium interactions in Se accumulation act through the metabolism of sulphur-containing amino acids in wheat plants. Further, the substantial Zn enrichment in flour paralleled to the increase of amino acid profiles such as aspartate, glutamate, glycine and lysine, but not to the total amino acid content. Overall, wheat was successfully biofortified with Zn and Se through combined foliar applications, although an antagonistic impact of ZnSO4 spray on the magnitude of Se biofortification occurred in some cases.