Seed Endophyte bacteria enhance drought stress tolerance in Hordeum vulgare by regulating, physiological characteristics, antioxidants and minerals uptake

Growth stimulating bacteria help remediate dry arid soil and plant stress. Here, <i>Pseudomonas</i> sp. and <i>Pantoea</i> sp. we used to study the stress ecology of <i>Hordeum vulgare</i> and the environmental impact of water deficit on soil characteristics, growth, photosynthesis apparatus, mineral acquisition and antioxidiant defense. Plants inoculated with <i>Pseudomonas</i> or <i>Pantoea</i> had significantly higher (about 2 folds) soil carbon flux (soil respiration), chlorophyll levels (18%), net photosynthetic rate (33% in <i>Pantoea</i> and 54% in <i>Pseudomonas</i>), (44%) stomatal conductance than uninoculated plants in stressed conditions. Both bacterial strains improved leaf growth (23-29%) and root development under well-watered conditions but reduced around (25%) root biomass under drought. Plants inoculated with <i>Pseudomonas</i> or <i>Pantoea</i> under drought also increased of about 27% leaf respiration and transpiration (48%) but decreased water use efficiency, photoinhibition (91%), and the risk of oxidative stress (ETR/A) (49%). Drought stress increased most of the studied antioxidant enzymatic activities in the plants inoculated with <i>Pseudomonas</i> or <i>Pantoea</i>, which reduce the membrane damage and protect plants form oxidative defenses. Drought stress increased K⁺ acquisition around 50% in both shoots inoculated with <i>Pseudomonas</i> or <i>Pantoea</i> relative to non-stressed plants. Plants inoculated with <i>Pseudomonas</i> or <i>Pantoea</i> increased shoot Na⁺ while root Na⁺ only increased in plants inoculated with <i>Pseudomonas</i> in stressed conditions. Drought stress increased shoot Mg²⁺ in plants inoculated with <i>Pseudomonas</i> or <i>Pantoea</i> but did not affect Ca²⁺ relative to non-stressed plants. Drought stress increased about 70% K⁺/Na⁺ ratio only in plants inoculated with <i>Pseudomonas</i> relative to non-stressed plants. Our results indicate that inoculating barley with the studied bacterial strains increases plant biomass and can therefore play a role in the environmental remediation of drylands for food production.