Physiological Mechanism Of Exogenous EBR And NO Enhancing Salt And Drought Tolerance Of Ceratoides Arborescens

Ceratoides arborescens belongs to Ceratoides.It is a perennial and strong xerophytic semi-shrub and it often grows in arid areas.C.arborescens has rich nutrition,good palatability,and high feed value.It is an important forage grass in desert areas and has strong adaptability to salt,alkali and arid environments.Brassinolide（BRs）is a type of polyhydroxylated steroid plant hormones,which can induce plant tolerance to a variety of stresses;nitric oxide（NO）is an important signal transduction molecule in the organism.It plays a key role in many physiological processes such as plant growth,development and stress resistance regulation.This paper takes C.arborescens as the research object,and analyzes the changes in physiological and biochemical indexes of C.arborescens seedlings under different concentrations of neutral salt（Na Cl）,alkaline salt（9Na HCO₃:1Na₂CO₃）and drought（PEG-6000）.The physiological characteristics of C.arborescens in response to different environmental stresses by externally applying 2,4-epibrassinolide（EBR）and NO donor SNP to C.arborescens seedlings under salt and drought stress,and the growth indexes of the seedlings under the combined treatments were observed.The degree of membrane damage,while detecting changes in osmotic adjustment,photosynthesis,ion balance and antioxidant enzyme activity,comprehensive analysis of the physiological effects and regulatory mechanisms of EBR and NO in enhancing salt and drought tolerance of C.arborescens.The results of the study laid the foundation for clarifying the stress response mechanism of C.arborescens,and at the same time provided technical support for the use of this plant to improve the desert saline soil and the grassland resource environment.The main results are as follows:1.Detect the growth indicators of C.arborescens seedlings under different concentrations of neutral salt（Na Cl）,alkaline salt（9Na HCO₃:1Na₂CO₃）and PEG-6000 stresses,and found that the three stresses all lead to its fresh weight,root length,and relative content.The water volume and chlorophyll content decreased in different degrees,and the relative conductivity increased significantly.Among them,the alkaline salt treatment had a greater impact on the growth indicators of C.arborescens seedlings,indicating that the three stresses all caused the growth of C.arborescens seedlings.And membrane damage,in which the adverse effects of alkaline salt stress on plants are greater than drought and neutral salt stress.2.Detect the physiological and biochemical indexes of C.arborescens seedlings under three stress treatments.The results showed that antioxidant enzymes（SOD,POD,CAT,APX）activities and MDA,O^2-and H₂O₂contents were significantly higher under alkaline salt treatments with neutral salt and drought,and indicated that alkaline salt causes greater oxidative damage to C.arborescens.Analysis of photosynthetic characteristics showed that salt and drought stress have different effects on the photosynthesis of C.arborescens seedlings.Salt stress can cause the Ci value of C.arborescens increased first and then decreased,while Pn value decreased continuously.Under drought stress,Ci and Pn value of C.arborescens Leaves decreased continuously.3.Exogenous EBR pretreatment can increase the biomass of C.arborescens seedlings under stress,increase the activities of antioxidant enzymes POD,SOD,CAT,APX in the leaves and reduce the content of MDA,O^2-and H₂O₂to alleviate the stress caused by it oxidative damage;significantly increased the chlorophyll content,net photosynthetic rate Pn and stomatal conductance Gs of C.arborescens leaves under stress,indicating that EBR may increase the photosynthetic efficiency of plants by promoting the opening of stomata to induce C.arborescens plants to produce resistance to salt and drought stress.Exogenous EBR treatment significantly reduced the Na⁺content in the roots and leaves of C.arborescens seedlings under stress,increased Ca²⁺and Mg²⁺contents in the leaves,and decreased Na⁺/K⁺contents,indicating that exogenous EBR increased the antioxidant enzymes activity,ion homeostasis,photosynthetic efficiency,enhanced the survival ability of C.arborescens under stress.4.Low concentration of SNP can obviously promote the growth of C.arborescens seedlings,while high concentration of SNP will inhibit the growth of plants.Treatment of C.arborescens seedlings with 70μM SNP had the best effect.SNP pretreatment can significantly increase the growth indicators of C.arborescens seedlings under three stresses,such as fresh weight,root length,and relative leaf water content,and alleviate the stress’s growth inhibition and damage to the plant.Compared with single stress,the activities of antioxidant enzymes（SOD,POD,CAT,APX）and the contents of nonenzymatic antioxidants GSH,GSSH,osmotic adjustment substance pro and soluble sugar were significantly increased,while the accumulation of reactive oxygen species and the content of MDA were decreased,which indicated that exogenous NO increased the antioxidant and osmotic adjustment ability of plants;exogenous no significantly decreased the content of Na⁺in roots and leaves,The contents of K⁺,Ca²⁺and Mg²⁺in leaves were significantly increased,and the ratio of Na⁺/K⁺in cells was maintained at a low level;meanwhile,Pn,Tr and Gs in photosynthetic system were also significantly increased,which indicated that exogenous NO could improve the ion homeostasis and photosynthetic efficiency of C.arborescens seedlings under stress to a certain extent,and enhance the survival ability of plants under stress.