Abstract
Microbial inoculation in drought challenged rice triggered multipronged steps at enzymatic, non-enzymatic and gene expression level. These multifarious modulations in plants were related to stress tolerance mechanisms. Drought suppressed growth of rice plants but inoculation with Trichoderma, Pseudomonas and their combination minimized the impact of watering regime. Induced PAL gene expression and enzyme activity due to microbial inoculation led to increased accumulation of polyphenolics in plants. Enhanced antioxidant concentration of polyphenolics from microbe inoculated and drought challenged plants showed substantially high values of DPPH, ABTS, Fe-ion reducing power and Fe-ion chelation activity, which established the role of polyphenolic extract as free radical scavengers. Activation of superoxide dismutase that catalyzes superoxide (O2−) and leads to the accumulation of H2O2 was linked with the hypersensitive cell death response in leaves. Microbial inoculation in plants enhanced activity of peroxidase, ascorbate peroxidase, glutathione peroxidase and glutathione reductase enzymes. This has further contributed in reducing ROS burden in plants. Genes of key metabolic pathways including phenylpropanoid (PAL), superoxide dismutation (SODs), H2O2 peroxidation (APX, PO) and oxidative defense response (CAT) were over-expressed due to microbial inoculation. Enhanced expression of OSPiP linked to less-water permeability, drought-adaptation gene DHN and dehydration related stress inducible DREB gene in rice inoculated with microbial inoculants after drought challenge was also reported. The impact of Pseudomonas on gene expression was consistently remained the most prominent. These findings suggested that microbial inoculation directly caused over-expression of genes linked with defense processes in plants challenged with drought stress. Enhanced enzymatic and non-enzymatic antioxidant reactions that helped in minimizing antioxidative load, were the repercussions of enhanced gene expression in microbe inoculated plants. These mechanisms contributed strongly towards stress mitigation. The study demonstrated that microbial inoculants were successful in improving intrinsic biochemical and molecular capabilities of rice plants under stress. Results encouraged us to advocate that the practice of growing plants with microbial inoculants may find strategic place in raising crops under abiotic stressed environments.
Highlights
Microbial inoculation in drought challenged rice triggered multipronged steps at enzymatic, nonenzymatic and gene expression level
We examined elicitation of superoxide dismutation (SODs), PO, Ascorbate peroxidase (APX), catalase, Glutathione reductase (GR) and Guaiacol peroxidase (GPX) as key inducible enzymes in drought stressed plants subsequently inoculated with microbial species
The results strongly suggested that microbial inoculation had a positive role in the over-expression of the genes linked with the peroxidation of H2O2 in the plants challenged with the drought
Summary
Microbial inoculation in drought challenged rice triggered multipronged steps at enzymatic, nonenzymatic and gene expression level. Increased production of antioxidative enzymes like SOD, POD, CAT, GPX and GST9 and the accumulation of antioxidant compounds such as carotenoids[10] and phenylpropanoids[11] successfully help plants reduce their load of ROS within the cells These processes cumulatively help plants mitigate burden of oxidative mechanisms while maintaining their growth and development under stressful conditions. The most natural inhabitants of the soils and the rhizosphere, the specific ecological niche associated with the root vicinity, tremendously influence plant growth and productivity[17,18] Their interaction with the plant root system constitutes the most complex and intricate biological phenomenon that helps plant activate their adaptive capabilities against drought stress through induced defense mechanisms[19,20]. The observations warrant microbial inoculation as an efficient stress mitigation strategy for rice crop challenged with drought stress in the fields
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