Ultrafine bubbles alleviated osmotic stress in soybean seedlings

Growth promotion through application of ultrafine bubbles (UFBs) was observed in several crop species grown under suboptimal conditions. In the current study, mitigation of osmotic stress through polyethylene glycol 6000 (PEG6000) was analyzed in soybean seedlings to assess the effects of UFB on plants under soil drought stress. In no-nutrient conditions, growth suppression due to osmotic stress was increasingly mitigated by UFB application as stress intensity increased. Shoot biomass of UFB-treated plants (at all examined PEG6000 concentrations) exceeded to that of the absolute control. Production of superoxide radicals (O-2(-)) under osmotic stress was 1.5-fold higher than that in the control, whereas that in UFB-treated plant showed a similar level as the absolute control. The reduction of O-2(-) through treatment with UFB may help mitigate osmotic stress. In conclusion, this study quantitatively showed that UFB was effective in reducing osmotic stress in soybean seedlings.