Effects of foliar application of zinc and selenium on the antioxidant enzyme activities and zinc and selenium contents in millet grains

Objectives  Many researchers have tried to increase the content of zinc and selenium in grains through application of exogenous Zn and Se. We studied the interactions of Zn and Se application on antioxidant enzyme activity and the accumulation of Zn and Se in grains, to provide theoretical support for the production of Zn and Se enriched millet.

Methods  Field trials were carried out for two years in 2016 to 2017, with millet cultivar of Jigu 21 as tested materials. Zn levels of 0, 2.25 and 4.50 kg/hm² and Se levels of 0, 30 and 60 g/hm² were used to construct seven treatments. The activities of superoxide dismutase (SOD), peroxidase (POD) and glutathione peroxidase (GSH-Px) in millet leaves, the content and uptake of Zn and Se in grains were analyzed, and the yield of millet was weighed.

Results  Foliar application of Zn and Se had significant effect on the activity of antioxidant enzymes and the uptake of Zn and Se in grains. At the low level of Zn (2.25 kg/hm²), both the activity of SOD and GSH-Px increased first and then decreased with the increase of Se levels; At the low Se level (30 g/hm²), SOD and GSH-Px activity increased with Zn levels, however, the combination of high Zn and high Se was not conducive to the improvement of antioxidant enzyme activity. The highest activity was obtained under combined application of low Zn and low Se. Foliar application of Zn and Se had significant effect on uptake and accumulation of Zn and Se in grain. The single application of Zn and Se significantly increased Zn and Se contents in grains. At low Zn rate, combining application with low Se rate promoted the absorption of Zn, with high Se rate decreased Zn uptake. At low Se rate, increasing Zn rates benefited the uptake of Se, while at high Se rate, increasing Zn rate did not promote the Se uptake. The highest grain yield was obtained at combined application of low Zn and low Se.

Conclusions  Foliar application of Zn and Se could significantly increase the activities of antioxidant enzymes in leaves and the Zn and Se contents in grain. When combined application, the spray concentration of Zn and Se should be considered carefully. At low spray rate (Zn 2.25 kg/hm², Se 30 g/hm²), Zn and Se has synergist to some extent, high rate Zn does not inhibit Se uptake, while high Se rate inhibits Zn uptake.