The Physiological And Molecular Mechanisms Of Salt Tolerance Regulation In Grape Seedlings By Strigolactones

Soil salinization is a global problem that limits the safe cultivation of crops.Currently,approximately 33%of irrigated farmland across the world has been adversely affected by salinization.As an important economic specialty crop in my country,grapes have been widely cultivated for its strong adaptability and high economic benefits.However,unfavorable natural conditions and unreasonable irrigation methods have resulted in the growing issue of soil salinization in grape-growing regions across our country.This has significantly hindered the development of the grape industry.Therefore,studying how to enhance the salt tolerance of grapes is of strategic importance.Strigolactones are a new phytohormone that participates in various biological processes in plants.They have been extensively studied for their ability to enhance plant stress resistance.However,it remains unclear whether exogenous strigolactones can alleviate salt stress damage in grape seedlings and what specific mechanism they employ to achieve this.In this study,the’Merlot’grape was sprayed the synthetic analogue of strigolactones(rac-GR24)to explore the effect of exogenous strigolactones on the physiological and biochemical characteristics of grape seedlings under salt stress,and then to analysis the action mechanism of strigolactones in alleviating the effects of salt stress in grapes,in order to provide the theoretical basis and technical support for grape cultivation on saline soils.The main results of the study are as follows.(1)The exogenous GR24 treatment alleviated the inhibitory effects of salt stress on the growth and development of grape seedlings.Salt stress results in yellowing and wilting of grape leaves,as well as stunted growth.Exogenous GR24 treatment significantly promoted the growth of grape seedlings under salt stress,with the most significant effect after 1μmol/L GR24treatment,increasing plant height and biomass by 32%and 60%,respectively,compared to the salt treatment alone.Furthermore,the root system of the grape seedlings showed greater development after exogenous GR24 treatment,with root length and vigor increasing by 43.1%and 66%,respectively,which significantly alleviated the growth inhibition caused by salt stress.(2)Exogenous GR24 treatment significantly increased the photosynthetic ability of grape seedlings under salt stress.When subjected to salt stress,grape seedlings experienced a significant reduction in their photosynthetic pigment content and photosynthetic parameters.However,the treatment of exogenous GR24 resulted in a notable increase of 18%,35%and 22%in chlorophyll a,chlorophyll b,and total chlorophyll content,respectively,as compared to the salt treatment alone.Moreover,exogenous GR24 also significantly improved the photosynthetic indicators and maximum photochemical efficiency,indicating that exogenous GR24 enhanced photosynthetic capacity of grape seedlings by alleviating the damage to the photosynthetic system caused by salt stress.(3)Exogenous GR24 treatment enhanced the antioxidant activity of grape seedlings under salt stress.Exogenous application of GR24 under salt stress enhanced the activity of antioxidant enzymes and the content of non-enzymatic antioxidants in grape seedlings,reducing the content of hydrogen peroxide and superoxide anion in seedlings by 33%and 80%compared to salt treatment alone,thus alleviating oxidative damage caused by salt stress,decreasing the malondialdehyde content and relative conductivity of leaves,and ensuring the stability of cell membranes.(4)Exogenous GR24 treatment promotes ion transport by increasing the expression activity of the H~+-ATPase and H~+-PPase proton pumps in the vesicle membrane,and by maintaining high levels of SOS1 and NHX expression and inducing SKOR gene expression,thereby reducing cytoplasmic Na~+accumulation and maintaining a stable Na~+/K~+ratio.(5)Based on transcriptome sequencing analysis,the key differential genes for exogenous GR24 regulation of salt tolerance in grape seedlings were mainly enriched in the phytohormone signaling,photosynthesis-antennae protein and calcium signaling pathways,and most of the differential genes were induced by exogenous GR24 and up-regulated in expression.(6)VvMAX2 is a key regulatory gene of strigolactones for improving salt tolerance in grape seedlings.Exogenous application of GR24 under salt stress induced Vv MAX2 gene expression at a high level and overexpression of Vv MAX2 improves resistance to salt stress and osmotic stress in Arabidopsis.(7)VvMAX2 can interact with VSK3,VSK9 and VSK11 proteins,and the expression patterns of Vv MAX2 and VSK3,VSK9 and VSK11 are highly similar.They are mainly expressed in leaves,and the expression levels can be induced by salt stress,suggesting that Vv MAX2 can function synergistically with VSK3,VSK9 and VSK11 proteins for salinity tolerance in grape seedlings.It is suggested that exogenous strigolactones can effectively improve the tolerance of grapevine seedlings under salt stress.It regulates the morphological construction and the biochemical processes of grapevine seedlings by regulating key genes and major signalling pathways,thereby alleviating the negative effects of salt stress on grapevine seedlings and enhancing the growth and development of seedlings under salt stress.In this study,the functional characteristic of strigolactones to enhance salt stress resistance in grape seedlings was comprehensively revealed,and its specific action mechanism was analyzed,providing new ideas for resistant cultivation and breeding of grapes.