Green Synthesized Titanium Oxide Nanoparticles Promote Salt Tolerance in Soybean

Soybean is rich in protein and functional ingredients, which are in high demand as a food material; however, it is vulnerable to environmental stress. On the other hand, the application of chemically synthesized titanium oxide nanoparticles (TiO₂ NPs) promoted soybean growth even under salt stress. To further enhance the growth-promoting effect of TiO₂ NPs on soybeans, they were biologically synthesized using orange peel extract. Root elongation of soybeans suppressed by salt stress was restored to the control level by treatment with green synthesized (GS)-TiO₂ NPs. To clarify the promoting mechanism in soybean of GS-TiO₂ NPs under salt stress, immunoblot analysis was performed. The abundance of vacuolar H⁺-ATPase decreased in roots by salt stress was recovered with GS-TiO₂ NPs. In contrast, the abundance of glutathione reductase increased in roots and hypocotyls by salt stress was recovered with GS-TiO₂ NPs. Furthermore, hydrogen peroxide production increased in roots with salt stress that was restored by treatment with GS-TiO₂ NPs. These results suggest that GS-TiO₂ NPs may restore soybean growth by detoxifying hydrogen peroxide, which increases under salt stress, with upregulating reactive oxygen species scavenging systems.