Molecular Hydrogen Is Involved in Phytohormone Signaling and Stress Responses in Plants

Molecular hydrogen (H(2)) metabolism in bacteria and algae has been well studied from an industrial perspective because H(2) is viewed as a potential future energy source. A number of clinical trials have recently reported that H(2) is a therapeutic antioxidant and signaling molecule. Although H(2) metabolism in higher plants was reported in some early studies, its biological effects remain unclear. In this report, the biological effects of H(2) and its involvement in plant hormone signaling pathways and stress responses were determined. Antioxidant enzyme activity was found to be increased and the transcription of corresponding genes altered when the effects of H(2) on the germination of mung bean seeds treated with phytohormones was investigated. In addition, upregulation of several phytohormone receptor genes and genes that encode a few key factors involved in plant signaling pathways was detected in rice seedlings treated with HW. The transcription of putative rice hydrogenase genes, hydrogenase activity, and endogenous H(2) production were also determined. H(2) production was found to be induced by abscisic acid, ethylene, and jasmonate acid, salt, and drought stress and was consistent with hydrogenase activity and the expression of putative hydrogenase genes in rice seedlings. Together, these results suggest that H(2) may have an effect on rice stress tolerance by modulating the output of hormone signaling pathways.