Effects Of Exogenous MeJA And BR On Tomato Seed Germination And Seedling Growth Under Drought Stress

With the warming of the global temperature,the problem of water shortage has seriously affected agricultural production and also had a serious impact on the physiological characteristics of crops.Tomato（Solanum lycopersicum）is an important crop in arid and semi-arid regions,and has a large demand for water..In the previous study,the application of BR and/or MeJA can alleviate the damage caused by drought stress to plants and have a regulatory effect on seed germination,and can significantly improve the drought resistance of crops and reduce crop yield loss caused by drought stress.Recently,there are few studies on the effects of BR and/or MeJA on tomato seed germination and seedling growth under drought stress.Therefore,in the present study,’Xinhong 49’was used to study the effects of BR and/or MeJA treatments on seed germination index and seedling growth and physiological indexes of tomato under drought stress,of which to explore the alleviation effects of exogenous BR and/or MeJA treatment on tomato and provide an simple method for tomato drought tolerance.The main results are as follows:1.Effects of exogenous hormone on tomato seed germination and young rootsTo study the effects of exogenous MeJA and/or BR on seed germination,different concentration gradients MeJA and/or BR were carried out to test the germination.The results showed that,compared with the control group,5×10^-5μmol·L^-1MeJA treatment was the optimal concentration for seed germination and5×10^-6μmol·L^-1MeJA can promote the root growth,but inhibit the growth of buds;with the BR treatment of 10^-5μmol·L^-1,the seed germination was the best and also significantly increased root and shoot growth.In addition,the hormone mixed treatment,the better concentration is MeJA 5×10^-4μmol·L^-1with+BR 10^-5μmol·L^-1,which had obvious effects on seed germination and promoted the root and bud length.Taken together,our results showed that single hormone treatment has better affect on seed germination,root growth and bud growth than dual hormone treatment.Therefore,MeJA and/or BR at appropriate concentrations can promote tomato seed germination.2.Effects of exogenous hormones on the growth and development and physiological response of tomato seedlings under drought stress（1）we chose the 300 mmol/L mannitol or 15%PEG-6000 to mimic drought stress.In the present study,the optimal concentration of exogenous hormone sprays was determined,which was 0.1μmol·L^-1BR or100μmol·L^-1of MeJA,respectively.Seedlings were sprayed with 0.1μmol·L^-1BR,100μmol·L^-1MeJA,or0.1μmol·L^-1BR+100μmol·L^-1MeJA after drought stress,respectively,followed by water control to make it sustainable drought treatment..Under drought stress,compared with untreated tomato plants,the treatment groups had lower water loss rate,significantly higher net photosynthetic rate,stomatal conductance and transpiration rate,better growth state and lighter leaf wilt.（2）The activity of POD was the highest at 24 h or 72 h after treatment under drought stress（300 mmol/L mannitol or 15%PEG-6000）after exogenous spraying of MeJA and was the highest at 24 h and 48 h,respectively by praying BR.Furthermore,the POD activity showed significant differently at 24 h while spraying BR+MeJA.Moreover,compared to the control,the activity of SOD and the content of CAT were also significantly increased.The experimental results showed that after drought stress,the activities of POD,CAT and SOD increased gradually with the passage of drought stress time,but the activities were further increased after hormone treatment.（3）Treatment with 300 mmol/L mannitol or 15%PEG-6000 inhibited the growth of seedlings,increased the accumulation level of reactive oxygen species,increased the contents of MDA,O₂^-and H₂O₂in leaves,and decreased the content of Pro,thereby making the seedlings resistant to drought weaken.However,exogenous hormone（BR and/or MeJA）treatment alleviated the inhibitory effect of stress on seedling growth.Compared with simple drought,the contents of O₂^-,H₂O₂and MDA were relatively reduced,while the osmotic adjustment substances proline,soluble sugar and betaine.The content was significantly increased in the late drought period to enhance the ability of seedlings to withstand drought.