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. The use of ZnO NPs in this way can provide benefits to humans, but also has potential risks. ZnO NPs inevitably enter the environment during their production and use, which affects the ecological environment and crop growth. In order to investigate the phenotype, physiology, and gene expression of barley (Hordeum vulgare L.) seedlings under 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 stage through hydroponics. The results showed that the density of brown spots on the leaf surface increased with increasing ZnO NPs concentration. ZnO NPs stress inhibited the root growth of barley seedlings, and P21 was the most sensitive. Furthermore, ZnO NPs stress could stimulate plants to produce a large number of reactive oxygen species (ROS), resulting in an imbalance between the production and removal of ROS and membrane lipid peroxidation in plants. This imbalance inhibited the growth and development of the barley seedlings. With increasing ZnO NPs concentration, the activity of superoxide dismutase was gradually increased, the activity of catalase was progressively decreased, and the contents of malondialdehyde and proline were increased. Compared with the control, among six stress-related genes, the expression levels of five genes were downregulated and one gene was upregulated in the experimental group. This study preliminarily revealed the toxic effect of ZnO NPs on seedlings and the effect on the expression of stress-related resistance genes in different barley varieties.