The Physiological and Molecular Responses of Exogenous Selenium to Selenium Content and Fruit Quality in Walnut

To study the effect of exogenous selenium on fruit quality in walnut (Juglans regia L.), 8-year-old walnut(Qingxiang) was taken as the research object. In the fruit expansion stage, 300 mg/L of sodium selenate, yeastselenium and sodium selenite solutions were applied on the leaf of walnut, and the selenium levels in leaves,pericarp and kernel were determined at the ripening stage. The fruit quality, mineral nutrient content, antioxidantenzyme activity, and related genes’ expression were analyzed. The results showed that the three exogenousselenium increased the selenium levels in leaves, pericarp and kernel of walnut. They also significantly increasedfruit and kernel weights, and kernel linoleic acid, but markedly decreased kernel crude fat and saturated fatty acid.Selenium spraying promoted the absorption of mineral nutrients such as potassium and zinc, but inhibited theabsorption of calcium, and had no significant effect on iron and magnesium in the kernel. Three exogenousselenium increased the activities of superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase(APX), and catalase (CAT) significantly in the kernel. Except for sodium selenate treatment significantly reducedmalondialdehyde (MDA) content in the kernel, the other two selenium sources treatments had no significanteffect on MDA and hydrogen peroxide (H₂O₂) levels. They also increased the expression of JrCu/Zn-SOD, Jr2-CysPOD, JrCyt-APX and JrCAT in kernel, to different extents. These implies that, in the walnut fruit enlargementperiod, the foliar spraying selenium could increase the selenium content of walnut, affect the mineral nutrientabsorption, improve the antioxidant capacity and related genes’ expression, and reduce the degree of peroxide,and then improve the quality of fruit. Furthermore, yeast selenium showed the comprehensive effect of the best.