Downstream Signalling from Molecular Hydrogen

Molecular hydrogen (H(2)) is now considered part of the suite of small molecules that can control cellular activity. As such, H(2) has been suggested to be used in the therapy of diseases in humans and in plant science to enhance the growth and productivity of plants. Treatments of plants may involve the creation of hydrogen-rich water (HRW), which can then be applied to the foliage or roots systems of the plants. However, the molecular action of H(2) remains elusive. It has been suggested that the presence of H(2) may act as an antioxidant or on the antioxidant capacity of cells, perhaps through the scavenging of hydroxyl radicals. H(2) may act through influencing heme oxygenase activity or through the interaction with reactive nitrogen species. However, controversy exists around all the mechanisms suggested. Here, the downstream mechanisms in which H(2) may be involved are critically reviewed, with a particular emphasis on the H(2) mitigation of stress responses. Hopefully, this review will provide insight that may inform future research in this area.