The Alleviation Effect Of Exogenous Melatonin And 2,4-Epibrassinolide On Saline-alkali Stress Of Rosa Multiflora Insignis

The increasing soil salinization seriously threatens the growth of plants and limits the production and garden application of rose in saline-alkali areas.Rosa multiflora is the most commonly used rootstock in rose production.Improving the saline-alkali tolerance of Rosa multiflora can easily and efficiently improve the saline-alkali tolerance of grafted seedlings of different rose varieties,thereby expanding the cultivation and application range of rose.Studies have shown that the application of exogenous substances can improve the saline-alkali tolerance of plants,but what substances and what concentration can improve the saline-alkali tolerance of Rosa multiflora and the mechanism of improving the saline-alkali tolerance are unknown.In this study,the 2-year-old cutting seedlings of Rosa multiflora,an excellent rose rootstock,were used as experimental materials.The seedlings of Rosa multiflora were treated with different concentrations of melatonin and 2,4-epibrassinolide（spraying method and root irrigation method）,and the appropriate exogenous substance treatment methods were screened by plant phenotypic changes.On this basis,the physiological and biochemical processes of growth phenotype,photosynthesis,plasma membrane permeability,antioxidant enzyme activity and osmotic regulation of Rosa multiflora were investigated.The effects of MT and EBR on plant growth and physiological response under saline-alkaline stress with0.5%saline-alkaline content in Rosa multiflora soil were analyzed.The alleviation effect and physiological mechanism of exogenous melatonin and 2,4-epibrassinolide on Rosa multiflora were clarified,and the most suitable concentration for improving saline-alkaline tolerance of Rosa multiflora was screened out.The main results are as follows:1.Screening of the best exogenous substance treatment method:By comparing the apparent morphology of plant leaves treated with MT and EBR solution by spraying method or root-irrigation method,350μmol·L^-1MT,0.05 mg·L^-1EBR and 0.6 mg·L^-1EBR were applied.There was no significant difference in leaf morphological growth between the two treatment methods,while the other six concentrations of plant phenotype showed that the number of leaf expansion,plant growth rate and luxuriant degree of root-irrigation method were significantly better than those of spraying method.2.The effects of exogenous melatonin and 2,4-epibrassinolide on the apparent damage of Rosa multiflora under saline-alkali stress:350,250 and 150μmol·L^-1MT could alleviate the saline-alkali stress of Rosa multiflora to varying degrees,which was significantly different from that of saline-alkali,and the phenomenon of chlorosis and yellowing of leaves decreased.0.1 mg·L^-1EBR,0.2 mg·L^-1EBR,0.4 mg·L^-1EBR can also alleviate saline-alkali stress,improve the relative growth of plants in different degrees,and inhibit the curling and yellowing of leaves.3.Effects of exogenous melatonin and 2,4-epibrassinolide on photosynthesis of Rosa multiflora under saline-alkali stress:Exogenous application of four concentrations of MT solution increased P_n,T_rand G_sof Rosa multiflora leaves,and slowed down the increase of C_iin leaves.With the decrease of MT concentration,P_n,T_rand G_sof leaves increased first and then decreased,while C_idecreased first and then increased,and reached the maximum and minimum values at 250μmol·L^-1MT.Exogenous application of five concentrations of EBR solution,the P_n,T_rand G_sof leaves increased first and then decreased with the increase of EBR concentration,and C_idecreased first and then increased,and reached the maximum and minimum values at 0.2 mg·L^-1EBR.4.Effects of exogenous melatonin and 2,4-epibrassinolide on physiological indexes of Rosa multiflora under saline-alkali stress:when the stress time was the same,the relative conductivity and MDA content of exogenous MT with different concentrations decreased first and then increased with the decrease of concentration,and its antioxidant enzyme activity and osmotic adjustment substances increased first and then decreased with the decrease of MT concentration.The relative conductivity and MDA content of exogenous EBR with different concentrations decreased first and then increased with the increase of concentration,and the antioxidant enzyme activity and osmotic adjustment substances increased first and then decreased with the increase of EBR concentration.5.In this experiment,after applying different concentrations of MT or EBR under saline-alkali stress,9 physiological and biochemical indexes were increased or decreased to varying degrees compared with the control,indicating that there were some differences in the ability of MT and EBR to alleviate saline-alkali.Through membership function analysis and comparison of comprehensive scores,it can be concluded that the order of exogenous substances to alleviate saline-alkaline is 0.2 mg·L^-1EBR>250μmol·L^-1MT>350μmol·L^-1MT>0.4 mg·L^-1EBR>150μmol·L^-1MT>0.1 mg·L^-1EBR>50μmol·L^-1MT>0.05mg·L^-1EBR>0.6 mg·L^-1EBR.