Downstream signalling from molecular hydrogen

Molecular hydrogen (H2) is now considered to be a part of the suite of small molecules which can control cellular activity. As such it has been suggested to be used in the therapy of diseases in humans but also to be used 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 H2 re-mains quite elusive. It has been suggested that the presence of H2 may act as an antioxidant, or, on the antioxidant capacity of cells, perhaps through the scavenging of hydroxyl radicals. Further more, H2 may act through an influence on heme oxygenase activity, or through the interaction with reactive nitrogen species. However, there is controversy around all the mechanisms suggested. Here, the downstream mechanisms in which H2 may be involved are critically re-viewed, with a particular emphasis on H2 mitigation of stress responses. Hopefully, this review will give an insight which may inform future research in this area