Oxidative Capacity of Nanobubbles and Its Effect on Seed Germination

Nanobubbles (NBs) have been reported to be effective at accelerating the metabolism of living organisms, but the mechanism is not yet well understood. In this study, the production of reactive oxygen species (ROS) by NBs and its effect on seed germinations were investigated. The fluorescence response of APF to NB water was measured. It changed depending on the NB number density which decreased with storage time. This indicated that NBs could produce ROS and the amount of ROS had positive correlation with the NB number density. The fluorescence intensity of APF increases linearly with the concentration of H₂O₂ in the range of 0-1 mM. Just after the NB generation, the oxidative capacities represented by amount of ROS of oxygen NB water and gas-mixture (air + nitrogen) NB water were estimated to be equivalent to 0.5 and 0.3 mM H₂O₂ respectively. The seed germination tests were performed in the NB water, distilled water and H₂O₂ solutions. The germination rate at each observation times of seeds submerged in gas-mixture NB water and 0.3 mM H₂O₂ solutions were both higher than those submerged in distilled water. The amounts of superoxide radicals in the seeds were detected using NBT staining. The results of absorbance data proved that the amounts of O₂^•- in seeds submerged in gas-mixture NB water and in 0.3 mM H₂O₂ solution were similar and significantly higher than those in the distilled water. These results indicated that moderate level of exogenous ROS produced by NB water played an important role in seed germination.