Effects Of Exogenous 24-Epibrassinolide On Photosynthetic Characteristics Of Tea Plants Under Salt And Drought Stress

Tea plants[Camellia sinensis（L.）O.Kuntze]is an important raw material for the production and supply of non-alcoholic beverages in the world.It is a typical C3 plant and mainly used for picking young shoots.Compared with other crops,the net photosynthetic rate of tea plants is relatively low,and it varies with tea species,development stages and environmental conditions.Photosynthesis provides substrate and energy for the synthesis of primary metabolites,and secondary metabolites are obtained from the primary metabolites.The three major types of secondary metabolites,tea polyphenols,theanine and caffeine,are the three major quality components that affect the quality of tea.Therefore,tea plant photosynthesis not only affects its yield,but also has an inseparable relationship with its quality.In addition,with the intensification of global soil salinization and the frequent occurrence of extreme weather such as high temperature and drought,salt stress and drought stress have become important factors affecting the growth and development of tea plants,cultivation and promotion,as well as the yield and quality.24-Epibrassinolide（EBR）is a kind of sterol plant hormone,which is widely used in the research of plant growth,development and stress response,but the research reporting on the effect of exogenous application of EBR on the photosynthetic characteristics and salt and drought resistance of tea plants is less.In this paper,‘Zhongcha 108’was used as the test material.On the one hand,in order to explore the regulation mechanism of EBR on the photosynthetic characteristics of tea plants,the effects of spraying different concentrations of EBR(0.10,0.30,0.50mg·L^-1)on the chlorophyll content,stomata opening,photosynthetic gas exchange parameters and related genes of tea leaves was studied;on the other hand,by studing the effects of photosynthetic gas exchange parameters,chlorophyll fluorescence parameters,malondialdehyde（MDA）content,antioxidant enzyme activity and related antioxidant enzyme biosynthetic gene expression in tea leaves,explore the mitigation mechanism of EBR on tea plants under salt and drought stress.The main research results of this paper are as follows:1.The effects of spraying EBR with different concentrations(0.10,0.30,0.50mg·L^-1)on the chlorophyll content,stomatal aperture,photosynthetic gas exchange parameters and related gene expression of tea leaves were studied.The results show that spraying 0.10 and 0.30 mg·L^-1EBR on leaves significantly increased the chlorophyll content of tea leaves on the first day after treatment,which increased 38.89%and22.22%,respectively,compared with the control.On the third and fifth days after treatment,the stomatal aperture of tea leaves treated with 0.10 and 0.30 mg·L^-1EBR increased significantly.On the first and fifth days after treatment,spraying EBR significantly increased the net photosynthetic rate of tea leaves.At the same time,EBR treatment could significantly up-regulate the expressions of genes involved in BR biosynthesis,chlorophyll biosynthesis,and carbon assimilation.In conclusion,exogenous EBR can regulate the chlorophyll content and stomata opening of tea leaves by regulating the expression of related genes,thereby improving the photosynthesis capacity of tea plants.2.The effects of 0.10 mg·L^-1EBR treatment on the photosynthetic gas exchange parameters,chlorophyll fluorescence parameters,MDA content,antioxidant enzyme activity and related antioxidant enzyme biosynthesis genes in tea leaves under salt and drought stress were studied.The results showed that spraying EBR on foliage can significantly increase the net photosynthetic rate（P_n）,stomatal conductance（G_s）,and maximum photochemical efficiency（Fv/Fm）of tea leaves under salt and drought stress;in addition,EBR treatment can significantly reduce MDA content,regulate related genes to increase the activity of superoxide dismutase（SOD）,peroxidase（POD）,catalase（CAT）and ascorbate peroxidase（APX）of the tea plants.These results indicate that EBR relieves the inhibition of photosynthesis of tea leaves under salt and drought stress through non-stomatal factors,and effectively uses a variety of antioxidant pathways,alleviating the damage of salt and drought stress to tea plants.