Ros Mediating Ethylene And Auxin Regulating The Adventitious Roots Of Cucumber Under Waterlogging(Cucumis Sativus.L)

Cucumber is one kind of the most important vegetable in China.The cultivation area of cucumber in China was 116.44 hectares,and with annual production of 5431.59 million tons in 2013.As global warming and flood disasters occurred frequently,waterlogging has become one of the most frequent and extensive abiotic stresses that negatively influence crop growth and productivity,and in some case resulting in plant death.Cucumber is easily affected by heavy rain because of its shallow-rootedness,less developed aerenchyma,weak absorption ability and poor regeneration ability.However,the adventitious root can be formed in cucumber plants under waterlogging condition which can replace some function of taproot,for lightening the damage caused by waterlogging.The mechanisms regulating the adventitious root formation is unclear now.In present research,the waterlogging resistant cultivar of cucumber "Zaoer-N"was applied.The role of ROS,ethylene and auxin in the adventitious root formation under waterlogging were analyzed,and the possible mechanism that regulated the adventitious root formation were discussed.The main results were as follows:(1)ROS was accumulated in the hypocotyl of cucumber under waterlogging condition.The adventitious roots formation was promoted by H2O2 treatment,inhibited by DMTU treatment.In addition,we found that the expression level of Csrbohl and Csrboh3 were up-regulated by waterlogging,which indicated that ROS was involved in the adventitious root formation under waterlogging condition.(2)The content of ethylene was increased in the hypocotyl of cucumber under waterlogging condition.The adventitious roots formation was promoted by ACC treatment,and inhibited by 1-MCP treatment.The gene expression of Csacs4,Csacs7,Csaco1,Csaco3,and Csaco9 was up-regulated under waterlogging condition.Our results suggested that ethylene was one of regulators in the adventitious root formation under waterlogging condition.(3)Auxin level in the hypocotyl of cucumber was increased after waterlogging treatment.The adventitious roots formation was promoted by NAA treatment,and inhibited by NPA treatment,which indicated the important role of auxin in the induction of adventitious root formation.(4)For elucidating the mutual roles of ROS,ethylene and auxin in the formation of adventitious root,the ROS,ethylene and auxin levels were analyzed under H2O2,ACC and NAA treatment.The results showed that ROS was accumulated under waterlogging condition combined with ACC and NAA treatment,respectively.However,the ethylene and auxin content were not affected by H2O2 treatment,suggesting that ROS was in the downstream of signal transduction of ethylene and auxin during adventitious root formation.The auxin content was increased under waterlogging condition combined ACC treatment,and ethylene level was increased by waterlogging combined with NAA treatment.In a total,results indicated ethylene and auxin can affect each other,and finally promoted the ROS activity to form the root primordium.