Seed inoculation of desert-plant growth-promoting rhizobacteria induce biochemical alterations and develop resistance against water stress in wheat.

Water shortage limits agricultural productivity, so strategies to get higher yields in dry agricultural systems is vital to circumvent the effect of climate change and land-shortage. The plant rhizosphere harbors beneficial bacteria able to confer biotic/abiotic tolerance along with a positive impact on plant growth. Herein, three bacterial strains, Proteus mirabilis R2, Pseudomonas balearica RF-2 and Cronobacter sakazakii RF-4 (accessions: LS975374, LS975373, LS975370, respectively) isolated from native desert-weeds were investigated for their response to improve wheat growth under drought stress. The bacteria showed drought tolerance up to 20% polyethylene glycol (PEG; -0.6 MPa), and salt (65-97 g l-1 ), 1-aminocyclopropane-1-carboxylate (ACC)-deaminase activity, P/Zn/K-solubilization, calcite degradation, IAA, and siderophore production. The plant growth-promoting rhizobacteria (PGPR) were evaluated on wheat under water stress. The P. balearica strain RF-2 primed seeds showed a maximum promptness index and germination index under PEG-stress, that is, 68% and 100%, respectively. Inoculation significantly improved plant growth, leaf area, and biomass under water stress. P. mirabilis R2 inoculated plant leaves showed the highest water contents as compared to the plants inoculated with other strains. C. sakazakii RF-4 inoculated plants showed minimum cell injury, electrolyte leakage, and maximum cell membrane stability at PEG stress. After 13 days exposure to drought, C. sakazakii RF-4 treated plants showed an overall higher expression of cytosolic ascorbate peroxidase (cAPX) and ribulose-bisphosphate carboxylase (rbcL) genes. The activity of stress-induced catalase and polyphenol oxidase was reduced, while that of peroxidase and superoxide dismutase increased after inoculation but the response was temporal. Taken together, this data explains that different PGPR (especially C. sakazakii RF-4) modulate differential responses in wheat that eventually leads towards drought tolerance, hence, it has the potential to enhance crop production in arid regions.

Plant survival under drought stress: Implications, adaptive responses, and integrated rhizosphere management strategy for stress mitigation.

In many regions of the world, the incidence and extent of drought spells are predicted to increase which will create considerable pressure on global agricultural yields. Most likely among all the abiotic stresses, drought has the strongest effect on soil biota and plants along with complex environmental effects on other ecological systems. Plants being sessile appears the least resilient where drought creates osmotic stress, limits nutrient mobility due to soil heterogeneity, and reduces nutrient access to plant roots. Drought tolerance is a complex quantitative trait controlled by many genes and is one of the difficult traits to study and characterize. Nevertheless, existing studies on drought have indicated the mechanisms of drought resistance in plants on the morphological, physiological, and molecular basis and strategies have been devised to cope with the drought stress such as mass screening, breeding, marker-assisted selection, exogenous application of hormones or osmoprotectants and or engineering for drought resistance. These strategies have largely ignored the role of the rhizosphere in the plant's drought response. Studies have shown that soil microbes have a substantial role in modulation of plant response towards biotic and abiotic stress including drought. This response is complex and involves alteration in host root system architecture through hormones, osmoregulation, signaling through reactive oxygen species (ROS), induction of systemic tolerance (IST), production of large chain extracellular polysaccharides (EPS), and transcriptional regulation of host stress response genes. This review focuses on the integrated rhizosphere management strategy for drought stress mitigation in plants with a special focus on rhizosphere management. This combinatorial approach may include rhizosphere engineering by addition of drought-tolerant bacteria, nanoparticles, liquid nano clay (LNC), nutrients, organic matter, along with plant-modification with next-generation genome editing tool (e.g., CRISPR/Cas9) for quickly addressing emerging challenges in agriculture. Furthermore, large volumes of rainwater and wastewater generated daily can be smartly recycled and reused for agriculture. Farmers and other stakeholders will get a proper knowledge-exchange and an ideal road map to utilize available technologies effectively and to translate the measures into successful plant-water stress management. The proposed approach is cost-effective, eco-friendly, user-friendly, and will impart long-lasting benefits on agriculture and ecosystem and reduce vulnerability to climate change.

The Development of Antibiotics Based on Nanostructured Manganese Oxide; Understanding Mechanism from Fundamental Aspects to Application.

The emergence of bacterial resistance to currently available antibiotics emphasized the urgent need for new antibacterial agents. Nanotechnology-based approaches are substantially contributing to the development of effective and better-formulated antibiotics. Here, we report the synthesis of stable manganese oxide nanostructures (MnO NS) by a facile, one-step, microwave-assisted method. Asprepared MnO NS were thoroughly characterized by atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM), dynamic light scattering (DLS), UV-Visible spectroscopy and X-ray powder diffraction (XRD). UV-Visible spectra give a sharp absorption peak at a maximum wavelength of 430 nm showed surface plasmon resonance (SPR). X-ray diffraction (XRD) profile demonstrated pure phase and crystalline nature of nanostructures. Morphological investigations by a scanning electron microscope showed good dispersity with spherical particles possessing a size range between 10-100 nm. Atomic force microscope data exhibited that the average size of MnO NS can be controlled between 25 nm to 150 nm by a three-fold increment in the amount of stabilizer (o-phenylenediamine). Antimicrobial activity of MnO NS on both gram-positive (Bacillus subtilis) and gram-negative (Escherichia coli) bacterial strains showed that prepared nanostructures were effective against microorganisms. Further, this antibacterial activity was found to be dependent on nanoparticles (NPs) size and bacterial species. These were more effective against Bacillus subtilis (B. subtilis) as compared to Escherichia coli (E. coli). Considering the results together, this study paves the way for the formulation of similar nanostructures as effective antibiotics to kill other pathogens by a more biocompatible platform. This is the first report to synthesize the MnO NS by green approach and its antibacterial application.