Microbial Siderophores in Rhizophere Interactions in Heavy Metal-Containing Environments

Heavy metals may affect microbial and plant physiological processes in two ways: (i) an excess of the metals induces elevated levels of reactive oxygen species (ROS), and ROS-induced oxidative stress, in turn, affects microbial and plant cellular and metabolic processes and hence, their growth. (ii) Metals interfere with iron acquisition, which, together with pH-induced insolubility, enhances iron deficiency symptoms in microbes and plants. Iron being essential, microbes and plants have evolved strategies for its acquisition. Basically, most microbes and graminaceous plants elicit low-molecular-weight, high-affinity, iron-scavenging compounds, siderophores. In contrast, dicotyledonous and non-grass monocotyledonous plants elaborate an increased iron reductase activity, coupled with release of phenolics and extrusion of protons. However, such plants can benefit from siderophore production by associated microbes. Despite their preference for iron, siderophores bind other metals, albeit with reduced affinity. Binding of siderophores to metals dramatically alters free metal concentrations and can, thus, play a bioprotective role in microbes and plants. Therefore, mechanisms that reduce the bioavailability of toxic metals in the environment for microbes, as well as provide plants with improved access to metals determine eco-toxicologically relevant metal concentrations in the soil, and their influence in microbe-assisted phytoremediation. The objective of the study was, therefore, to study the role of siderophores produced by Streptomyces spp in metal-induced microbial and plant rhizosphere processes and to evaluate their application in chelator-assisted phytoremediation of metal pollution

Fortification of micronutrients for efficient agronomic production: a review

International audienceAbstractMicronutrients are essential mineral elements required for both plant and human development. However, micronutrients are often lacking in soils, crop, and food. Micronutrients are therefore used as fertilizer to increase crop productivity, especially when the application of conventional NPK fertilizers is not efficient. Here, we review the application of micronutrients in crop production. Reports show that micronutrients enhance crop nutritional quality, crop yield, biomass production, and resiliency to drought, pest, and diseases. These positive effects range from 10 to 70 %, dependent on the micronutrient, and occur with or without NPK fertilization. We discuss the uptake by plants of micronutrients as nanosize particulate materials, relative to conventional uptake of ionic nutrients. We also show that packaging of micronutrients as nanoparticles could have more profound effects on crop responses and fertilizer use efficiency, compared to conventional salts or bulk oxides

Unlocking the multiple public good services from balanced fertilizers

Fertilizers produce over half of the world’s food and permit less encroachment into pristine lands. Yet, the low uptake efficiency by crop plants causes nutrient losses that drive global change. Mitigating measures have been insufficient to address the problems, and policy interventions, NGO involvement, and R&D investments have been too insignificant to transform the fertilizer sector. Here, we discuss the contribution of balanced mineral fertilizers to increasing the nutritional value of crop produce to improve human nutrition and health; healthier plants to reduce biocide use; plant robustness to enhance tolerance to abiotic stresses; and increased metabolite production to improve taste and shelf-life. We reflect on raising awareness about these multiple fertilizer-based public good services for realizing several Sustainable Development Goals which can be achieved through a comprehensive nutrient assessment to catalyze transformation in research, policy and industry

Revisiting fertilisers and fertilisation strategies for improved nutrient uptake by plants

Meeting human needs within the ecological limits of our planet calls for continuous reflection on, and redesigning of, agricultural technologies and practices. Such technologies include fertilisers, the discovery and use of which have been one of the key factors for increasing crop yield, agricultural productivity and food security. Fertiliser use comes, however, at an environmental cost, and fertilisers have also not been a very economically effective production factor to lift many poor farmers out of poverty, especially in African countries where application on poor soils of unbalanced compositions of nutrients in fertilisers has shown limited impact on yield increase. Agronomic practices to apply existing mineral fertilisers, primarily containing N, P and K, at the right time, the right place, in the right amount, and of the right composition can improve the use efficiency of fertilisers. However, the overall progress to reduce the negative side effects is inadequate for the desired transformation toward sustainable agriculture in poor countries. Globally, there have been no fundamental reflections about the role and functioning of mineral fertilisers over the past 5 decades or more, and compared to other sectors, dismal investments have been made in mineral fertiliser research and development (R&D). In this paper, we reflect on current fertilisers and propose a more deliberate adoption of knowledge of plant physiological processes—including the diversity of mineral nutrient uptake mechanisms, their translocation and metabolism—as an entry point in identifying the physicochemical “packaging” of nutrients, their composition, amount and timing of application to meet plant physiological needs for improved instantaneous uptake. In addition to delivery through the root, we suggest that efforts be redoubled with several other uptake avenues, which as of now are at best haphazard, for the delivery of nutrients to the plant, including above ground parts and seed coating. Furthermore, ecological processes, including nutrient-specific interactions in plant and soil, plant-microorganism symbiosis, and nanotechnology, have to be exploited to enhance nutrient uptake. It is hoped that concerted R&D efforts will be pursued to achieve these strategies

Time dependent release of microplastics from disposable face masks poses cyto-genotoxic risks in Allium cepa

The use of disposable face masks (DFMs) increased during the COVID-19 pandemic and has become a threat to the environment due to the release of microplastics (MPs). Although many reports have characterized and explored the release of MPs from DFMs and their effects in aquatic ecosystems, there is a lack of investigation into the effects in terrestrial plants. This report aims to fill this research gap by characterizing whole mask leachates (WMLs) collected at different time points and examining their toxicity on Allium cepa, a terrestrial model plant. Various analytical techniques including FE-SEM, FT-IR, and Raman spectroscopy were used to identify MPs in WMLs. The MPs are composed of polypropylene mostly and the concentration of smaller-sized MPs increased with leachate release time. The WMLs showed a MP concentration-dependent cytogenotoxic effect (72 %, 50 %, and 31 %, on 1, 5, and 11-day WMLs, respectively) on A. cepa root cells due to elevated oxidative stress (19 %, 45 %, and 70 %, on 1, 5, and 11-day WMLs, respectively). Heavy metal content of the WMLs was negligible and, thus, not a significant contributor to toxicity in the plant. Overall, this report highlights the fate of DFMs in the environment and their biological impacts in a model plant

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doctor rerum naturalium (Dr. rer. nat.

Effects of Manganese Nanoparticle Exposure on Nutrient Acquisition in Wheat (Triticum aestivum L.)

Nanoparticles are used in a variety of products, including fertilizer-nutrients and agro-pesticides. However, due to heightened reactivity of nano-scale materials, the effects of nanoparticle nutrients on crops can be more dramatic when compared to non nano-scale nutrients. This study evaluated the effect of nano manganese-(Mn) on wheat yield and nutrient acquisition, relative to bulk and ionic-Mn. Wheat was exposed to the Mn types in soil (6 mg/kg/plant), and nano-Mn was repeated in foliar application. Plant growth, grain yield, nutrient acquisition, and residual soil nutrients were assessed. When compared to the control, all Mn types significantly (p < 0.05) reduced shoot N by 9–18%. However, nano-Mn in soil exhibited other subtle effects on nutrient acquisition that were different from ionic or bulk-Mn, including reductions in shoot Mn (25%), P (33%), and K (7%) contents, and increase (30%) in soil residual nitrate-N. Despite lowering shoot Mn, nano-Mn resulted in a higher grain Mn translocation efficiency (22%), as compared to salt-Mn (20%), bulk-Mn (21%), and control (16%). When compared to soil, foliar exposure to nano-Mn exhibited significant differences: greater shoot (37%) and grain (12%) Mn contents; less (40%) soil nitrate-N; and, more soil (17%) and shoot (43%) P. These findings indicate that exposure to nano-scale Mn in soil could affect plants in subtle ways, differing from bulk or ionic-Mn, suggesting caution in its use in agriculture. Applying nano Mn as a foliar treatment could enable greater control on plant responses

Compliance Testing of Hemp (<i>Cannabis sativa</i> L.) Cultivars for Total Delta-9 THC and Total CBD Using Gas Chromatography with Flame Ionization Detection

The United States Agriculture Improvement Act passed in December of 2018 legalized the growing of Cannabis sativa containing not more than 0.3% total Delta-9 tetrahydrocannabinol (THC) in the country. While Cannabis sativa has been cultivated for hundreds of years, the illegal status of the plant in the United States, and elsewhere, has hindered the development of plant cultivars that meet this legal definition. To assess sampling strategies, and conformance to the THC limit, 14 cultivars of hemp were grown and tested by using gas chromatography with flame ionization detection for total delta-9 THC and total cannabidiol (CBD) during 2020, 2021 and 2022. Each year, samples of fresh plant material were collected from each cultivar weekly, beginning in mid-August and ending in late October, to examine the rate of increase in THC and CBD for different cultivars and select individual plants. The sampling demonstrated that both CBD and THC increase rapidly over a 1–2-week time frame with maximum concentrations (about 16% and 0.6%, respectively) around late September to early October. The testing of individual plants on the same day for select cultivars showed that while the ratio of CBD to THC remains constant (about 20:1 in compliant hemp) during the growing season, the individual plants are highly variable in concentration. Whereas previous studies have shown cultivar-dependent variability in THC production, this study demonstrated a novel plant-to-plant variability in the levels of THC within the same hemp cultivar. Understanding variability within and between hemp cultivars is useful to determine field sampling strategies and to assess the risk of crop embargoes to growers by compliance regulators

Effect of complexing ligands on the surface adsorption, internalization, and bioresponse of copper and cadmium in a soil bacterium, Pseudomonas putida

Environmental quality criteria for metals toxic to soil and water organisms, using the free ion activity model or the biotic ligand model, are based on the concept that the major form of the metal available to the organism is the free metal ion, yet various metal complexes are bioavailable to a variety of soil and water organisms. We test here whether neutral copper or cadmium sulfates, negatively-charged copper or cadmium citrates and positively-charged copper acetate and cadmium chloride are bioavailable to a soil bacterium, Pseudomonas putida. Adsorption onto the cell surface and uptake into the periplasm and cytoplasm of this Gram-negative root colonizing bacterium was studied by adding a single concentration of Cu or Cd and varying the concentration of the ligands to complex 10-100% of the metal. Metal association from the complexes on and within the cell was defined using selective extraction procedures and compared with free ion controls using the Langmuir isotherm. Cellular responses also were assessed using a P. putida biosensor. Both uptake and bioresponse methodologies showed that P. putida was sensitive to the metal complexes. In particular, the bioresponse to Cu and Cd supplied as a citrate complex occurred with activities of free metal ions two orders of magnitude lower than for the control. We concluded that the tested metal complexes for Cu and Cd are taken up into the cell, where they trigger a bioresponse. We also discuss the implications of these findings on interactions between soil and water organisms and nanoparticles that release metal ions. © 2012 Elsevier Ltd