Assessing the role of ACC deaminase-producing bacteria in alleviating salinity stress and enhancing zinc uptake in plants by altering the root architecture of French bean (Phaseolus vulgaris) plants

Main ConclusionThe consortium inoculation with strains R1 and R4 modified the root system to boost seedling growth, increase the zinc content of French bean pods, and reduce salinity stress.The present study demonstrated the effect of two 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase-producing plant growth-promoting rhizobacteria (Pantoea agglomerans R1 and Pseudomonas fragi R4) alone and consortia on the root system development, French bean growth, and zinc content as well as salinity stress tolerance. Both the strains were characterized for ACC utilization activity (426.23 and 380.54 nmol alpha-ketobutyrate mg protein(-1) h(-1)), indole acetic acid (IAA) production, phosphate solubilization, ammonia, hydrogen cyanide (HCN), and siderophore production. The strains exhibited zinc solubilization in both plate and broth assays with zinc oxide and zinc carbonate as zinc sources as validated by atomic absorption spectroscopy (AAS). Single or combined inoculations with the selected strains significantly modulated the architectural and morphological traits of the root system of French bean plants. Furthermore, the application of R1and R4 consortia has enhanced zinc content in roots (60.83 mg kg(-1)), shoots (15.41 mg kg(-1)), and pods (30.04 mg kg(-1)) of French bean plants grown in ZnCO3 amended soil. In another set of pot experiments, the consortium bacterization has significantly enhanced length as well as fresh and dry biomass of roots and shoots of the French bean plant under saline stress conditions. Additionally, inoculation with ACC-degrading rhizobacterial strains has increased chlorophyll and carotenoid contents, osmoprotectant content, and antioxidative enzyme (catalase and peroxidase) activity in comparison to their counterparts exposed to salt treatments only. Current findings suggested ACC deaminase-producing rhizobacterial strains hold the potential to improve root architecture which in turn promotes plant growth under salt-stressed conditions as well as enhances micronutrient concentration in host plants.