Physiological And Molecular Mechanisms Of ?-naphthylacetic Acid Regulating Cold Resistance Of Brassica Campestris L.

The growth and development of plants are affected by unpredictable biotic and abiotic stresses.In order to survive in a changing environment,plants must evolve a powerful adaptive mechanism.Reactive oxygen species and plant hormones are important factors for plants to respond to biotic and abiotic stresses,the interaction of reactive oxygen species with plant hormone pathways enhances plant adaptation to adverse environments.In abiotic stresses,low temperature stress is one of the main stress conditions that limit crop yield.Low temperature will seriously affect the growth,development and geographical distribution of plants,and greatly reduce crop yield and quality.Compared with other plant hormones,auxin plays an important role in regulating the growth and development of plants.However,there are few reports on the role of exogenous auxins in response to low temperatures,some studies have pointed out that plants grow at low temperatures,there may be some connection with the auxin response.In this experiment,auxin-like synthetic agent ?-naphthylacetic acid was used to simulate auxin,and Brassica campestris L.was used as the research material,histochemical staining,plant physiological and biochemical and molecular biology techniques were combined,the effects of exogenous NAA on the distribution of reactive oxygen species,antioxidant enzyme activities and osmoregulatory substances content in Brassica campestris L.under low temperature stress were studied,as well as the NADPH oxidase gene,antioxidant enzyme gene,cold resistance transcription factor and MAP kinase gene,the main conclusions are as follows:1.The method of histochemical staining was used to observe the root tips of Brassica campestris L..The results showed that the distribution of ROS in Brassica campestris L.roots was different under different treatments,compared with the control,the accumulation of ROS in root tips increased significantly under low temperature stress,and the most widely distributed ROS,and the addition of exogenous NAA at the same time of low temperature stress can reduce the accumulation of ROS,indicated that exogenous NAA adapted to the low temperature environment by regulating the changes of Brassica campestris L.ROS.In addition,low temperature stress caused plasma membrane damage in Brassica campestris L.roots,and the addition of appropriate concentration of exogenous NAA at the same time under low temperature stress alleviated the damage of plasma membrane in Brassica campestris L.roots.2.The contents of free proline and soluble sugar in Brassica campestris L.leaves increased under low temperature stress,compared with low temperature alone,the content of both proline and soluble sugar increased significantly after exogenous NAA and low temperature combined treatment,indicated that Brassica campestris L.can be enhanced by exogenous NAA,adjusted the content of substances to withstand the low temperature environment.Under low temperature stress,the chlorophyll content of Brassica campestris L.leaves decreased,added exogenous NAA at the same time caused the increase of chlorophyll content.Low temperature stress induced the accumulation of MDA,and the combination of exogenous NAA and low temperature stress reduced the accumulation of MDA,indicated that the membrane lipid peroxidation damage degree of Brassica campestris L.leaves was reduced.3.NADPH oxidase gene(Rboh A-Rboh G),antioxidant enzyme genes(CAT,SOD,APX and GR),cold-resistant transcription factor(ICE1 and CBF)and MAP kinase genes(MPK3,MPK4 and MPK6)were induced by low temperature,compared with low temperature stress alone,exogenous NAA increased the transcription level of the above genes under low temperature stress,indicated that these genes played an important role in Brassica campestris L.resistance to low temperature stress,in the composite treatment of exogenous NAA and low temperature stress respectively added DPI(NADPH oxidase inhibitors),DMTU(H2O2 scavenger),U0126(MAPKK-specific blocker)and Tungstate(nitrate reductase inhibitors),the expression levels of these genes have declined to varying degrees compared to the composite treatment,indicateed that NADPH oxidase,H2O2,MAP kinase signal pathway and NO are involved in the regulation of cold stress by exogenous NAA,respectively.