The Physiological Response Of Rhododendron Delavayi Franch. To Regulating Drought Tolerance By Brassinosterid(BR)

Rhododendron is a ornamental cultivation flower with high-grade landscaping and has great market potential which is used as Lantern Festival flowers.However,drought stress is one of key environmental factors that restricts the application of Rhododendron in garden landscape.The early transcriptome sequencing revealed that the genes involved in the brassinosteroid(BR)metabolic pathway were highly enriched,and it was speculated that the BR metabolic pathway might play an important role in the drought response process of Rhododendron delavayi.In this experiment,R.delavayi was used as the experimental materials,which has good drought tolerances.Under drought stress,different concentrations of 2,4-Epibrassinolide were sprayed through the leaves of R.delavayi,in order to select the optimum BR concentration for improving the drought resistance of R.delavayi.On the basis of this,the effects of exogenous EBR treatment on photosynthetic capacity,antioxidant system and osmotic adjustment substances of R.delavayi were researched to explore the physiological mechanism of exogenous EBR regulating the adaptation of R.delavayi to drought.The main results were as follows:1.Under drought stress,with the increase of BR treatment concentration,the net photosynthetic rate(Pn),transpiration rate(Tr),stomatal conductance(Gs),intercellular CO2 concentration(Ci),maximum net photosynthetic rate(Pmax),light compensation point(LCP),light saturation point(LSP),PSII reaction center excitation energy capture efficiency(Fv'/Fm'),Actual photochemical efficiency(?PS?),the photochemical quenching(qP),Apparent electron transport rate(ETR),early morning leaf water potential and noon leaf water potential showed a gradual upward trend.What's more,there was no significant difference in maximum quantum efficiency of photosystem II(Fv/Fm)and chlorophyll content between treatments,and the content of malondialdehyde(MDA),and the activity of superoxide dismutase(SOD)were trend of decrease,the content of proline and soluble protein trend of decrease too.While the content of soluble sugar and Peroxidase activity(POD)gradually increased,but there was no significant difference between the treatments.It indicated that the application of exogenous BR could maintain a good water state and high photosynthetic capacity,and reduce the degree of membrane lipid peroxidation damage,which could improve the drought tolerance of the R.delavayi.In the test range,and that the effect of 5?g·L-1 on drought resistance was better.2.Under drought stress,The Pn,Gs,Tr,Pmax,LSP,AQE,Fv/Fm,Fv'/Fm',?PS?,NPQ,ETR and proline contents of BR plants treated with R.delavayi were higher than those of drought treatment.While MDA content,SOD enzyme activity,POD enzyme activity,soluble sugar content and soluble protein content were lower than those without BR under drought treatment.And during the experiment,there was little difference between the BR treatment and the normal water supply treatment.It indicated that the BR treatment mainly increased the PSII reaction center and the photosynthetic electron transport rate,but reduced the openness of the Pheat dissipation,and effectively improved the photosynthetic capacity of the R.delavayi,and increased the osmotic adjustment substance by reducing the degree of membrane lipid peroxidation.The content was effective to alleviate the adverse effects of drought and improve the drought-tolerance of R.delavayi.