Physiological mechanisms of zinc oxide nanoparticles alleviating aluminum stress in soybean

Objective This study evaluated the effects of different zinc oxide nanoparticles (ZnO NPs) contents on the growth and physiological characteristics of Glycine max (Linn.) Merr. under aluminum (Al) stress, aiming to provide some reference for the application of metal nanomaterials in agriculture.

Method In a pot experiment, Al resistant cultivar ‘Huachun 2’ and Al sensitive cultivar ‘Huachun 6’ were selected and treated with ZnO NPs in various dosages of (0, 25, 50, 100 and 150 mg/kg) under 0.3 g/kg Al stress conditions, to investigate the effects of ZnO NPs on soybean physiological indicators (fresh weight, root length and chlorophyll content), total superoxide dismutase (T-SOD) activity and malondialdehyde (MDA) concentration.

Result Al stress significantly reduced the fresh weight and root length of ‘Huachun 6’, and increased its MDA concentration. For ‘Huachun 2’, a significant increase in its chlorophyll a and chlorophyll b content was observed, while there was no significant effect on other indicators. Application of ZnO NPs under no Al stress conditions increased the fresh weight, root length and SOD activity of both ‘Huachun 6’ and ‘Huachun 2’. When ZnO NPs were applied at various dosages under Al stress, ‘Huachun 6’ gained 13.2%−100.4% in fresh weight and 7.8%−35.8% in root length, respectively, while ‘Huachun 2’ reached its highest fresh weight at 150 mg/kg ZnO NPs. The chlorophyll a content of both ‘Huachun 6’ and ‘Huachun 2’ reached the highest value under 25 mg/kg ZnO NPs treatment under Al stress. Different levels of ZnO NPs had no significant effect on the chlorophyll b content of ‘Huachun 6’ and significantly reduced the chlorophyll b content of ‘Huachun 2’, reaching the lowest value (3.5 mg/g) at 100 mg/kg ZnO NPs. As ZnO NPs content increased, the T-SOD activity of ‘Huachun 6’ increased, and that of ‘Huachun 2’ reached the peak (820 U/g) at 50 mg/kg ZnO NPs, and then showed a decreasing trend. The minimum MDA concentration of ‘Huachun 6’ and ‘Huachun 2’ occurred at 25 and 50 mg/kg of ZnO NPs treatment, respectively.

Conclusion Al stress severely affects the growth and development of soybean, while the application of ZnO NPs, to some extent, can alleviate the negative effects of Al stress on soybean, and improve the growth and development of the plants.