Mechanism Of Brassinosteroids In Improving Resistance To Botrytis Cinerea And Drought In Tomato And Study On The Changes In Chlorophyll Fluorescence Characteristics Induced By Different Stresses

Agriculture is the basis for economic and social development.The safe production and stable supply of agricultural products are related to the national economy and people’s livelihood.As an important part of agriculture,the vegetable industry in facilities has made an irreplaceable contribution to stabilizing the supply of agricultural products and improving the economic benefits of agriculture.However,there are still many problems in the production of facility vegetables in our country,facing many threats from biotic and abiotic stresses.In this paper,tomato（Solanum lycopersicum L.）was used as experimental material,B.c（Botrytis cinerea）as a representative of biotic stress,and drought stress as a representative of abiotic stress.The effects of endogenous brassinosteroids on defense against B.c and drought stress in tomato were studied,and the related mechanisms were described.At the same time,the effects of different stresses on chlorophyll fluorescence parameters were studied,and an attempt was made to establish a method for rapid diagnosis of the physiological status of greenhouse crops based on chlorophyll fluorescence technology.This article provides new ideas for improving the ability of crop plants to withstand stress as well as developing facility production monitoring system.The specific results of this paper are as follows:The specific results of this paper are as follows:1.Endogenous BR positively regulate the resistance to B.c and does not depend on the ethylene pathway in tomato plants.High level of endogenous BR material DWF-OE increased resistance to B.c;conversely,low level of endogenous BR mutant d^{^im}increased susceptibility to B.c.High level of endogenous BR promote the synthesis and release of ethylene.In the case of normal endogenous BR level,ethylene receptor deficiency reduced tomato resistance to B.c.In the case of normal endogenous BR level,ethylene receptor deficiency will reduce tomato resistance to B.c.However,in the case of increased endogenous BR level,tomatoes showed no significant difference in resistance to B.c regardless of absence of ethylene receptors.This shows that both BR and ethylene can positively regulate tomato resistance to B.c,and that BR improves the resistance of tomatoes to B.c independently of ethylene.In addition,the loss of BZR1,a transcription factor downstream of BR,increased tomato susceptibility to B.c.In conclusion,BR enhances the resistance of B.c to tomato through an ethylene-independent pathway,which may depend on BZR1.2.Endogenous BR can positively regulate the drought resistance of tomato and the main mechanisms are as follows:endogenous BR effectively reduce the stomatal aperture of tomato leaves,thus reducing the water loss caused by the transpiration pull,increasing the drought tolerance of tomato,rather than by reducing stomatal density and increasing root development.Endogenous BR was able to induce up-regulation of RBOH1 gene expression and increase of H₂O₂ content under control and drought stress conditions,and the accumulation of reactive oxygen species（ROS）was detected at the early stage of drought stress（48 h）,thus increasing the resistance of tomato to drought stress.Endogenous BR increased ABA content in tomato leaves by regulating ABA synthesis genes NCED1 and ABA degradation genes CYP707A1 and CYP707A2.Specifically,BR increased ABA content by inhibiting ABA-degrading genes CYP707A1 and CYP707A2 under normal water supply and positively regulating the ABA synthesis gene NCED1 in the case of water deficit.The above results indicated that endogenous BR may promote the accumulation of ROS by increasing the content of ABA,resulting in the decrease of stomatal opening and eventually increase the drought tolerance of tomato.3.Perturbation of plant metabolism caused by environmental stresses will cause the change of chlorophyll fluorescence characteristic value.In this paper,the fast continuous detection mode of Dual-PAM-100 Fluorescence Instrument was used to measure the fluorescence value and the corresponding time of the leaf,and the value of the variable“f”was calculated according to a custom formula.With time as the X-axle,and the value of“f”as the Y-axle the Origin software is used for plotting and fitting the curve to obtain the initial slope k₀.The actual photochemical efficiency of photosystem II of leaves,Y（II）,was measured using a Plant Fluorescence Imager.Taking k₀ as the X-axle and Y（II）as the Y-axle to make the scatter plot of the chlorophyll fluorescence vs time.According to the result of clustering analysis,the scatter is divided into several regions.The results showed that Y（II）of tomato plants exposed to different types of stress were all lower than 0.4,but Y（II）of control plants were all higher than 0.4.The chlorophyll fluorescence characteristics of plants exposed to different types of stress were classified into three groups,and the values of k₀ of the three groups are different with each other.Specifically,the values of k₀ under drought stress were all less than 2.5,and the values of k₀ under disease,high temperature and low light stress ranged from3.0 to 5.0,while the values of k₀ under nutrients deficiency were all above 5.0.It can be seen that different stress-induced chlorophyll fluorescence characteristics are not exactly the same.