Interactions Between a Plant Probiotic and Nanoparticles on Plant Responses Related to Drought Tolerance

Modulating plant-soil microcosm with green synthesized ZnONPs in arsenic contaminated soil

Biogenic nanoparticle (NP), derived from plant sources, is gaining prominence as a viable, cost-effective, sustainable, and biocompatible alternative for mitigating the extensive environmental impact of arsenic on the interplay between plant-soil system. Herein, the impact of green synthesized zinc oxide nanoparticles (ZnONPs) was assessed on Catharanthus roseus root system-associated enzymes and their possible impact on microbiome niches (rhizocompartments) and overall plant performance under arsenic (As) gradients. The application of ZnONPs at different concentrations successfully modified the arsenic uptake in various plant parts, with the root arsenic levels increasing 1.5 and 1.4-fold after 25 and 50 days, respectively, at medium concentration compared to the control. Moreover, ZnONPs gradients regulated the various soil enzyme activities. Notably, urease and catalase activities showed an increase when exposed to low concentrations of ZnONPs, whereas saccharase and acid phosphatase displayed the opposite pattern, showing increased activities under medium concentration which possibly in turn influence the plant root system associated microflora. The use of nonmetric multidimensional scaling ordination revealed a significant differentiation (with a significance level of p < 0.05) in the structure of both bacterial and fungal communities under different treatment conditions across root associated niches. Bacterial and fungal phyla level analysis showed that Proteobacteria and Basidiomycota displayed a significant increase in relative abundance under medium ZnONPs concentration, as opposed to low and high concentrations, respectively. Similarly, in depth genera level analysis revealed that Burkholderia, Halomonas, Thelephora and Sebacina exhibited a notably high relative abundance in both the rhizosphere and rhizoplane (the former refers to the soil region influenced by root exudates, while the latter is the root surface itself) under medium concentrations of ZnONPs, respectively. These adjustments to the plant root-associated microcosm likely play a role in protecting the plant from oxidative stress by regulating the plant's antioxidant system and overall biomass.

Changes in Metal-Chelating Metabolites Induced by Drought and a Root Microbiome in Wheat

The essential metals Cu, Zn, and Fe are involved in many activities required for normal and stress responses in plants and their microbiomes. This paper focuses on how drought and microbial root colonization influence shoot and rhizosphere metabolites with metal-chelation properties. Wheat seedlings, with and without a pseudomonad microbiome, were grown with normal watering or under water-deficit conditions. At harvest, metal-chelating metabolites (amino acids, low molecular weight organic acids (LMWOAs), phenolic acids, and the wheat siderophore) were assessed in shoots and rhizosphere solutions. Shoots accumulated amino acids with drought, but metabolites changed little due to microbial colonization, whereas the active microbiome generally reduced the metabolites in the rhizosphere solutions, a possible factor in the biocontrol of pathogen growth. Geochemical modeling with the rhizosphere metabolites predicted Fe formed Fe-Ca-gluconates, Zn was mainly present as ions, and Cu was chelated with the siderophore 2'-deoxymugineic acid, LMWOAs, and amino acids. Thus, changes in shoot and rhizosphere metabolites caused by drought and microbial root colonization have potential impacts on plant vigor and metal bioavailability.

Plant Nutrition: An Effective Way to Alleviate Abiotic Stress in Agricultural Crops

By the year 2050, the world’s population is predicted to have grown to around 9–10 billion people. The food demand in many countries continues to increase with population growth. Various abiotic stresses such as temperature, soil salinity and moisture all have an impact on plant growth and development at all levels of plant growth, including the overall plant, tissue cell, and even sub-cellular level. These abiotic stresses directly harm plants by causing protein denaturation and aggregation as well as increased fluidity of membrane lipids. In addition to direct effects, indirect damage also includes protein synthesis inhibition, protein breakdown, and membranous loss in chloroplasts and mitochondria. Abiotic stress during the reproductive stage results in flower drop, pollen sterility, pollen tube deformation, ovule abortion, and reduced yield. Plant nutrition is one of the most effective ways of reducing abiotic stress in agricultural crops. In this paper, we have discussed the effectiveness of different nutrients for alleviating abiotic stress. The roles of primary nutrients (nitrogen, phosphorous and potassium), secondary nutrients (calcium, magnesium and sulphur), micronutrients (zinc, boron, iron and copper), and beneficial nutrients (cobalt, selenium and silicon) in alleviating abiotic stress in crop plants are discussed.

Absence of Nanoparticle-Induced Drought Tolerance in Nutrient Sufficient Wheat Seedlings

Strategies to reduce crop losses due to drought are needed as climate variability affects agricultural productivity. Wheat (Triticum aestivum var. Juniper) growth in a nutrient-sufficient, solid growth matrix containing varied doses of CuO, ZnO, and SiO₂ nanoparticles (NPs) was used to evaluate NP mitigation of drought stress. NP amendments were at fertilizer levels, with maxima of 30 Cu, 20 Zn, and 200 Si (mg metal/kg matrix). Seeds of this drought-tolerant cultivar were inoculated with Pseudomonas chlororaphis O6 (PcO6) to provide a protective root microbiome. An 8 day drought imposed on 14 day-old wheat seedlings decreased shoot and root mass, shoot water content, and the quantum yield of photosystem II when compared to watered plants. PcO6 root colonization was not impaired by drought or NPs. A dose-dependent increase in the Cu, Zn, and Si from the NPs was observed from analysis of the rhizosphere solution, and this process was not affected by drought. Consequently, fertilizer concentrations of the NPs did not further improve drought tolerance in wheat seedlings under the growth conditions of adequate mineral nutrition and the presence of a beneficial microbiome. These findings suggest that potential NP benefits in promoting plant drought tolerance occur only under certain environmental conditions.

Zinc oxide nanoparticles: potential effects on soil properties, crop production, food processing, and food quality

The use of zinc oxide nanoparticles (ZnO NPs) is expected to increase soil fertility, crop productivity, and food quality. However, the potential effects of ZnO NP utilization should be deeply understood. This review highlights the behavior of ZnO NPs in soil and their interactions with the soil components. The review discusses the potential effects of ZnO NPs on plants and their mechanisms of action on plants and how these mechanisms are related to their physicochemical properties. The impact of current applications of ZnO NPs in the food industry is also discussed. Based on the literature reviewed, soil properties play a vital role in dispersing, aggregation, stability, bioavailability, and transport of ZnO NPs and their release into the soil. The transfer of ZnO NPs into the soil can affect the soil components, and subsequently, the structure of plants. The toxic effects of ZnO NPs on plants and microbes are caused by various mechanisms, mainly through the generation of reactive oxygen species, lysosomal destabilization, DNA damage, and the reduction of oxidative stress through direct penetration/liberation of Zn2+ ions in plant/microbe cells. The integration of ZnO NPs in food processing improves the properties of the relative ZnO NP-based nano-sensing, active packing, and food/feed bioactive ingredients delivery systems, leading to better food quality and safety. The unregulated/unsafe discharge concentrations of ZnO NPs into the soil, edible plant tissues, and processed foods raise environmental/safety concerns and adverse effects. Therefore, the safety issues related to ZnO NP applications in the soil, plants, and food are also discussed.

Abiotic stressors impact outer membrane vesicle composition in a beneficial rhizobacterium: Raman spectroscopy characterization

Outer membrane vesicles (OMVs) produced by Gram-negative bacteria have roles in cell-to-cell signaling, biofilm formation, and stress responses. Here, the effects of abiotic stressors on OMV contents and composition from biofilm cells of the plant health-promoting bacterium Pseudomonas chlororaphis O6 (PcO6) are examined. Two stressors relevant to this root-colonizing bacterium were examined: CuO nanoparticles (NPs)-a potential fertilizer and fungicide- and H₂O₂-released from roots during plant stress responses. Atomic force microscopy revealed 40–300 nm diameter OMVs from control and stressed biofilm cells. Raman spectroscopy with linear discriminant analysis (LDA) was used to identify changes in chemical profiles of PcO6 cells and resultant OMVs according to the cellular stressor with 84.7% and 83.3% accuracies, respectively. All OMVs had higher relative concentrations of proteins, lipids, and nucleic acids than PcO6 cells. The nucleic acid concentration in OMVs exhibited a cellular stressor-dependent increase: CuO NP-induced OMVs > H₂O₂-induced OMVs > control OMVs. Biochemical assays confirmed the presence of lipopolysaccharides, nucleic acids, and protein in OMVs; however, these assays did not discriminate OMV composition according to the cellular stressor. These results demonstrate the sensitivity of Raman spectroscopy using LDA to characterize and distinguish cellular stress effects on OMVs composition and contents.

Insights into plant-beneficial traits of probiotic Pseudomonas chlororaphis isolates

Pseudomonas chlororaphisisolates have been studied intensively for their beneficial traits.P. chlororaphisspecies function as probiotics in plants and fish, offering plants protection against microbes, nematodes and insects. In this review, we discuss the classification ofP. chlororaphisisolates within four subspecies; the shared traits include the production of coloured antimicrobial phenazines, high sequence identity between housekeeping genes and similar cellular fatty acid composition. The direct antimicrobial, insecticidal and nematocidal effects ofP. chlororaphisisolates are correlated with known metabolites. Other metabolites prime the plants for stress tolerance and participate in microbial cell signalling events and biofilm formation among other things. Formulations ofP. chlororaphisisolates and their metabolites are currently being commercialized for agricultural use.