Abstract
Bulk nanobubbles, measuring less than 200 nm in water, have shown their salient properties in promoting growth in various species of plants and orthodox seeds, and as potential drug-delivery carriers in medicine. Studies of recalcitrant seeds have reported markedly increased germination rates with gibberellin treatment; however, neither the mechanism promoting germination nor the implication for food safety is well elucidated. In our study, recalcitrant wasabi (Eutrema japonicum) seeds treated with bulk oxygen nanobubbles (BONB) containing K(+), Na(+), and Cl(-) (BONB-KNaCl) showed significantly accelerated germination. As germination progressed, 99% of K(+) ions in the BONB-KNaCl medium were absorbed by the seeds, whereas Ca(2+) ions were released. These results suggest that the germination mechanism involves the action of K(+) channels for migration of K(+) ions down their concentration gradient and Ca(2+) pumps for the movement of Ca(2+) ions, the first potential discovery in germination promotion in recalcitrant seeds using nutrient solutions with BONB-KNaCl.