Effects Of Drought And Exogenous H₂O₂ Feeding To Roots On Reactive Oxygen Species Metabolism In Robinia Pseudoacacia

The study about reactive oxygen species?ROS?involved with the signal transduction of plants has been the focus of researches in recent years.Previous experiments have affirmed that ROS could participate in induced regulation of stomatal conductance as signaling substances,yet,whether drought-induced ROS in roots could transmit above ground as a rootsourced signal and participate in the regulation of drought-induced stomatal closure remained obscure.Robinia pseudoacacia were taken as experimental material,using water-controlled potting and exogenous hydrogen peroxide?H₂O₂?feeding to the roots as treatment methods,the levels and distribution of both H₂O₂ and superoxide anion?O2-?,activities of antioxidant enzymes in leaves,the roots and the xylem and phloem sap under non-limiting soil water availability,medium water deficit,and severe water deficit,and the levels and distribution of H₂O₂ and activities of antioxidant enzymes in leaves and roots were investigated.The results showed that:?1?With decreasing water contents,H₂O₂ contents in leaves and H₂O₂ distribution in leaves veins saw a significant increase,H₂O₂ contents in coarse and fine roots showed the same trends of increase but not significant;O2-contents in leaves and roots also increased yet only showed significance under severe water deficit.Therefore,leaves were the organ where H₂O₂ accumulated and roots were the organ where O2-accumulated.The O2-levels were far lower than the H₂O₂ levels in R.pseudoacacia.Meanwhile,the levels of H₂O₂ and O2-in stem xylem sap significantly increased,but they were not affected by water deficit significantly.?2?Drought treatment could elevate the activities of CAT and POD in leaves and CAT in fine roots,but there were no significant changes under severe water deficit;the POD activity in roots significantly dropped with the extent of water deficit;and SOD activities in leaves and roots showed non-significant increase with the intensifying extent of water deficit.?3?By exogenous H₂O₂ fed to the roots,the H₂O₂ levels in leaves and the roots were increased with the increasing concentration of exogenous H₂O₂ treatment,and H₂O₂ distribution in leaves veins saw an increase too.With the increasing concentration of exogenous H₂O₂ treatment,the activities of SOD,CAT and POD in roots all significantly decreased,and the CAT activity in leaves increased gradually;under treatment of low H₂O₂ concentration,SOD and POD activities in leaves significantly increased compared with which in control groups.In conclusion,with increasing water deficit,the levels of H₂O₂ and O2-in leaves and the roots in R.pseudoacacia increased significantly;H₂O₂ could transport with stem xylem sap from underground organ to above ground and accumulate in leaves veins,and H₂O₂ which contact with roots could do the same;soil water deficit and exogenous H₂O₂ fed to the roots both could elevate activities of antioxidant enzymes in R.pseudoacacia.The researcher speculated that there is a certain level of H₂O₂ in stem xylem sap of R.pseudoacacia,and the H₂O₂ concentration could be affected by soil drought and exogenous H₂O₂ treatment on roots,and the antioxidant enzymes in leaves also changed.This result would contribute to further discussion and explanation on the question that whether the ROS burst induced by drought could participates as a root-sourced signal in stomatal closure.