Phenotype,Physiology, and Gene Expression of Barley Seedlings in Response to Nano Zinc Oxide Stress

In recent years, zinc oxide nanoparticles (ZnO NPs) have been widely used as zinc fertilizers and pesticides. Theuse of ZnO NPs in this way can provide benefits to humans, but also has potential risks. ZnO NPs inevitably enterthe environment during their production and use, which affects the ecological environment and crop growth. Inorder to investigate the phenotype, physiology, and gene expression of barley (Hordeum vulgare L.) seedlingsunder ZnO NPs stress, the barely cultivars ZJU3 (P21), Golden Promise (GP) and L23 were chosen for study.Different ZnO NPs concentrations were applied to compare the physiological and biochemical indexes of the barley seedlings and the responses of six stress-related genes, when seedlings were cultured to the two-leaf stagethrough hydroponics. The results showed that the density of brown spots on the leaf surface increased withincreasing ZnO NPs concentration. ZnO NPs stress inhibited the root growth of barley seedlings, and P21 wasthe most sensitive. Furthermore, ZnO NPs stress could stimulate plants to produce a large number of reactiveoxygen species (ROS), resulting in an imbalance between the production and removal of ROS and membranelipid peroxidation in plants. This imbalance inhibited the growth and development of the barley seedlings. Withincreasing ZnO NPs concentration, the activity of superoxide dismutase was gradually increased, the activity ofcatalase was progressively decreased, and the contents of malondialdehyde and proline were increased. Comparedwith the control, among six stress-related genes, the expression levels of five genes were downregulated and onegene was upregulated in the experimental group. This study preliminarily revealed the toxic effect of ZnO NPs onseedlings and the effect on the expression of stress-related resistance genes in different barley varieties.