Effects Of Volatile Organic Compounds Produced By Plant Growth Promoting Rhizobacteria On Plant Growth Under Saline-alkali Stress

Saline-alkali stress is an important factor hindering the development of global agriculture.The gradual expansion of the saline-alkali land area greatly impacts the sustainable development of agriculture.Therefore,it is particularly important to improve the saline-alkali environment for plant growth.At present,the interaction between plant growth promoting rhizobacteria(PGPR)with plants is considered to be an effective method to improve salinity resistance.PGPR promotes the growth and the ability to resist stress in plants.Among them,the release of volatile organic compounds is one of the growth-promoting mechanisms.Revealing volatile organic compounds with a growth promoting effect not only has important theoretical value but also has important practical significance for the development and utilization of PGPR preparations.To study the effect of volatile organic compounds produced by four plant growth promoting rhizobacteria 1-9,S₂5-12,POD₃25,and PLD₁2-1 on plant growth,Firstly,the growth promoting effect of volatile organic compounds was verified by the adsorption of activated carbon.The results showed that after the addition of activated carbon,the growth-promoting effect of VOCs produced by the strain was decreased,indicating that VOCs was the main factor that promoted the growth of plants under saline-alkali conditions.Different bacterial liquid were added dropwise to measure the root length and fresh weight.It was found that strain 1-9 and PLD₁2-1 had the best growth promotion effect at 15?L;the strain POD₃25 had the best growth promotion effect at 20?L and the strain S₂5-12had the best growth promotion effect at 25?L,indicating that the growth promoting effect of VOC_Sproduced by the strain on plants is related to the amount of bacterial liquid.The VOCs produced by four plant growth promoting rhizobacteria promoted the development of Arabidopsis root meristem under saline-alkali conditions.To explore the growth-promoting mechanism of VOCs produced by the four strains,we isolated and cultured CYCB1;1::GUS with the strains to observe their expression levels.It was found that the VOCs produced by the four strains promoted the expression of CYCB1;1::GUS under saline-alkali conditions.The results showed that the VOCs produced by the four strains promoted cell division was one of the main factors to promote the development of plant roots;When the strains and auxin signal transduction mutant tir 1-1,cytokinin signal transduction mutant arr 1.10,ethylene signal transduction mutant ein 2-5 and ethylene synthesis mutant acs 5-1 were cultured separately,we found that under saline-alkali conditions,the VOC_Sproduced by the four strains all promoted their growth to varying degrees,which means that the growth-promoting effect of VOCs on plants is not through the auxin signal transduction pathway,cytokinin signal transduction pathway,and ethylene pathway.Nonetheless,the increased expression of CYCB1;1::GUS suggested that the salinity tolerance of plants may be promoted by other cytokinin pathways or other means.In order to study the effect of VOCs produced by four plant growth promoting rhizobacteria on other plants,after isolating and culturing potato tissue culture seedlings and strains,it was found that the root development of potato tissue culture seedlings under alkali stress was also promoted without contact between the strains and potatoes.This shows that the VOCs produced by the strain can promote the growth and development of potato tissue culture seedlings.The VOCs produced by four plant growth promoting rhizobacteria under saline-alkali conditions were analyzed by SPME-GC-MS.The results showed that most of these substances were compounds such as ketones,esters,acids,ketones,and olefins.Growth promotion effect on Arabidopsis thaliana under saline-alkali conditions on two single substances 2-heptanone and 3-methyl-1-butanol,both of which have no obvious growth promotion effect.In conclusion,the VOCs produced by four plant growth promoting rhizobacteria can promote the development of Arabidopsis roots by promoting the development of root meristem and cell division under saline conditions.However,this promoting effect does not depend on the auxin signal transduction pathway,cytokinin signal transduction pathway,and ethylene pathway.This study lays the foundation for the better application of plant rhizosphere bacteria to actual production.