Effects Of Hydrogen On Adventitious Root Development In Cucumber Under Cadmium Stress

Cadmium is a toxic heavy metal and one of the main sources of pollution.It is very easy to be absorbed and accumulated in plants.Accumulation of cadmium affects the absorption of mineral nutrients in plants,inhibits photosynthesis and the growth of plants,finnal causes death of plants.Hydrogen?H₂?is a colorless,odorless,tasteless gas molecule.Recent studies have shown that hydrogen can promote adventitious root formation in plants.However,it is still unclear what effects H₂ plays on adventitious root formation in cadmium-induced stresses.In order to elucidate the role of H₂ in cadmium toxicity,the functional mechanism of hydrogen under cadmium toxicity on adventitious root formation of cucumber were discussed in this1.Compared with the control,the number of adventitious roots of cucumber decreased significantly under cadmium stress.However,after co-treatment with hydrogen-rich water?HRW?,the number of adventitious roots increased significantly.The HRW treatment plus Cd had a dose-dependent effect on the formation of adventitious roots in cucumber,and the 50%HRW in combination with Cd had the greatest effect.2.By measuring the content of malondialdehyde?MDA?,relative conductivity,and lipoxygenase?LOX?,we verified that H₂ could inhabit the increase of membrane lipid peroxidation induced by cadmium stress and to keep the stability of plasma membrane.3.Compared with the control,the contents of reactive oxygen species?O₂^-and H₂O₂?and thiobarbituric acid?TBARS?were significantly increased under cadmium stress.However,after HRW co-treatment with Cd,the contents of reactive oxygen species and TBARS were reduced.It was suggested that H₂ could alleviate the reactive oxygen species damage caused by cadmium stress on adventitious root formation.4.In comparison with the control,the content of osmotic regulator?soluble sugar,soluble protein,proline?under cadmium stress decreased significantly.Nevertheless,the HRW co-treatment with Cd,resulted in a significant increase on osmotic adjustment substances.It also showed that H₂ could relieve cadmium damage on adventitious roots by increasing the content of osmotic adjustment substances.5.Cadmium stress significantly reduced the activity of rooting-related enzymes?POD,PPO,IAAO?compared with the control,while Cd was applied into HRW treatment causing a significantly increase on root-related enzyme activities.The result shows that H₂ could relieve cadmium damage by increasing the activity of root-related enzymes and promoting the occurrence of adventitious roots.6.The Ascorbate-Glutathione Circulatory System?AsA-GSH?is an important pathway for free radicals scavenging in plants.Compared with the control,the contents of AsA and GSH were significantly decreased under cadmium stress,HRW plus Cd treatment significantly increased the contents of AsA and GSH compared with Cd treatment.At the same time,the ratios of AsA/DHA and GSH/GSSH were also significantly enhanced.It was shown that H₂ increased the antioxidant capacity of cucumber explants and reinforced the content of reductive antioxidants under HRW Cd treatment.Compared with Cd treatment,the expression levels of the APX,MDHAR,DHAR,and GR genes and the corresponding enzyme activities of the cucumber explants under HRW treatment in combination with Cd were increased.These data demonstrated that the relieve effect of H₂ on adventitious root development under cadmium stress by regulating the AsA-GSH cycle.