Insights into the Roles of Melatonin in Alleviating Heavy Metal Toxicity in Crop Plants

Alleviating heavy metal pollution in farmland soil, and heavy metal toxicity in plants is the focus of global agricultural environmental research. Melatonin is a kind of indoleamine compound that wide exists in organisms; it is currently known as an endogenous free radical scavenger with the strongest antioxidant effect. As a new plant growth regulator and signaling molecule, melatonin plays an important role in plant resistance to biotic or abiotic stress. Recent studies indicate that melatonin can effectively alleviate heavy metal toxicity in crop plants, which provides a new strategy to minimize heavy metal pollution in crop plants. This study summarizes the research progress on the role of melatonin in alleviating heavy metal toxicity in crop plants and the related physiological and ecological mechanisms such as reducing the concentration of heavy metals in the rhizosphere, fixing and regionally isolating of heavy metals, maintaining the mineral element balance, enhancing the antioxidant defense system and interacting with hormonal signaling. Furthermore, future prospects for the mechanism of melatonin in regulating heavy metal toxicity, the pathway regulating synthesis and catabolism, and the interaction mechanism of melatonin signaling and other phytohormones are presented in this paper, with the goal of providing a theoretical basis for controlling heavy metal ion accumulation in crop plants grown in contaminated soil.     

Signaling responses in plants to heavy metal stress

Heavy metal toxicity is one of the major abiotic stresses leading to hazardous health effects in animals and plants. Because of their high reactivity they can directly influence growth, senescence and energy synthesis processes. In this review a new indirect mechanism of heavy metal action is proposed. This mechanism is connected with the generation of reactive oxygen species (especially H₂O₂) and jasmonate and ethylene signaling pathways and shows that toxicity symptoms observed in plants may result from direct heavy metal influence as well as the activity of some signaling molecules induced by the stress action.     

Plant growth promoting rhizobacteria for sustainable agricultural practices with special reference to biotic and abiotic stresses

The most common, devastating problem in agriculture is plant (pathogenic) diseases and abiotic conditions which have a profound effect on growth and yield of the plant resulting in heavy losses. In order to prevent losses, different chemicals are used indiscriminately, which in turn lead to environmental pollution due to their persistence and toxicity yet employed to meet consumer demand. To fight ever increasing demand and indiscriminate use of chemical agents along with their devastating after effects in agriculture, we need less invasive, eco-friendly and most importantly sustainable practices. Plant growth promoting rhizobacteria (PGPR) influence different physiological activities of the plant through various mechanisms (metabolites, antibiotics, Induced Systemic Resistance and enzymes) and impart protection from pathogens as well as environmental stress factors. But, current applications are limited in this regard as mechanisms involved, field applications variance and lack of farmer awareness contributing majorly. Current review tries to provide comprehensive knowledge on the PGPR’s applications as plant protectant against pathogens & abiotic factors leading to sustainable agricultural practices.     

一氧化氮对植物重金属胁迫抗性的影响研究进展

一氧化氮(NO)作为一种重要的信号分子,在调节植物重金属胁迫抗性方面上起着非常重要的作用。综述了NO在植物体内的产生途径,重金属胁迫下植物体内内源NO含量的变化以及外源NO与内源NO对植物重金属胁迫抗性的影响。大量研究表明外源NO能够增强植物对重金属胁迫的抗性,一方面是通过增强植物细胞的抗氧化系统或直接清除活性氧,另一方面是通过影响植物对重金属的吸收以及重金属在植物细胞内的分布。然而内源NO在调节植物重金属胁迫抗性上的功能角色仍存在争议。有些研究表明内源NO是有益的,能够缓解重金属胁迫诱导的毒性;但是也有证据表明内源NO是有害的,能够通过促进植物对重金属的吸收以及对植物螯合素进行S-亚硝基化弱化其解毒功能,从而参与重金属诱导的毒害反应和细胞凋亡过程。     

纳米氧化锌和接种丛枝菌根真菌对大豆生长及营养吸收的影响

纳米氧化锌是应用最广的人工纳米颗粒(nanoparticles,NPs)之一,具有一定生物毒性。丛枝菌根(arbuscular mycorrhizal,AM)真菌能与陆地上80%以上的高等植物形成丛枝菌根共生体,并能改善宿主植物矿质营养,提高其抗逆性。然而纳米ZnO与丛枝菌根的关系尚不清楚。通过温室沙培盆栽试验,研究了施加不同水平纳米ZnO(0、500、1000、2000、3000 mg/kg)和接种AM真菌Acaulospora mellea对大豆生长及营养状况的影响。结果表明,3000 mg/kg的纳米ZnO显著抑制大豆植株生长,表现出植物毒性,在其他水平时没有显著影响。纳米ZnO在施加水平500、1000 mg/kg时没有抑制AM真菌对大豆根系的侵染,但是高施加水平(2000 mg/kg)时对AM真菌产生毒害,几乎完全抑制大豆根系菌根侵染。接种AM真菌仅在500 mg/kg纳米ZnO时显著促进大豆生长,增加大豆植株对P、K、N的吸收,降低根系Zn含量。纳米ZnO可能会持续释放锌离子,并抑制大豆根系对矿质营养元素的吸收,从而产生生物毒性,而AM真菌与大豆根系的共生可起到有益作用。     

耐非生物胁迫转基因水稻的培育——现在和未来

环境胁迫严重降低了作物产量,日益减少的耕地和膨胀的人口对世界粮食安全造成了威胁。长期以来,改善作物的抗逆性一直是农业生产的主要目标。水稻是重要的粮食作物之一,培育具有抗逆性的水稻品种对全球的粮食生产将产生重要影响。在改善水稻的抗逆性方面,转基因比传统方法更有发展潜力。近年来,已有许多抗逆相关基因转入水稻并获得了一些提高抗逆性的转基因植株,文章重点讨论了耐非生物胁迫转基因水稻的研究进展。     

Current applications of nanotechnology to develop plant growth inducer agents as an innovation strategy

Abstract

Nanotechnology has been proposed as an important tool and strategy for applying new products in agriculture at the nanometer scale in order to improve the food crop at sustainability and productivity levels for contributing with the agriculture security. Nanoparticles (NPs) have been planted as an intelligent material with a large contact surface per unit mass respect to bulk-products, allowing its effect to be exerted with greater efficiency in a specific point on a plant target. Currently, NPs have been studied to be applied to various species of monocotyledonous and dicotyledonous plants. Some NPs properties such as concentration, shape, size, composition and surface functionality have the ability to regulate the NPs growth effects on the plant during germination and seedling stages under controlled and field conditions. Furthermore, several studies have tried to explain the mechanism of uptake, translocation and accumulation of NPs inside the plant at the organ and cell level, but further studies are needed to determine specific mechanisms and exact action. Nevertheless, evaluation of the toxicity effects of NPs on physiological indexes of the plant is needed to determine the effective dose without producing adverse effects on the plant and food chain. It is noteworthy that studies have indicated that nanoparticles, regardless of their nature, can be efficient inducers of plant growth. However, a series of laboratory tests are required to optimize their application conditions and their specific physiological impact on plants. In this review, we summarize the knowledge about NPs application to induce plant growth to direct future studies in order to propose NPs for technological innovation.     

Assessing the Potential Role of Zinc Oxide Nanoparticles for Mitigating Cadmium Toxicity in Capsicum annuum L. Under In Vitro Conditions

Journal of Plant Growth Regulation - The application of metal and metal-oxide nanoparticles (NPs) in agriculture to mitigate the abiotic environmental stress factors and pollutants has gained...     

Toxicity impacts of chemically and biologically synthesized CuO nanoparticles on cell suspension cultures of <Emphasis Type="Italic">Nicotiana tabacum</Emphasis>

Nanotechnology has quite a lot of applications in various fields of industrial sectors like food and agriculture. Although nanotechnology can improve the quality of life, its possible associated risks should be assessed. Here copper oxide nanoparticles (CuO NPs) were synthesized by chemical (polymer pyrolysis) and biological (green) methods with an average size of 30 and 44 nm, respectively. Afterwards, a cell biology approach was applied to evaluate the toxic effects of chemically and biologically synthesized CuO nanoparticles on tobacco cell suspension cultures. Both types of CuO nanoparticles significantly dropped the viability of the cells in a dose and time dependent manner. Accordingly, tobacco cells were found to increase the activity of antioxidant enzymes after 48 h of exposure to nanoparticles. The production of reactive oxygen species (ROS) and malondialdehyde (MDA) in a dose dependent manner was also observed. Assessment of the toxicity of CuO NPs revealed that chemically synthesized NPs were more toxic than biologically synthesized ones. It can be concluded that the organic components of the plant extract as capping agents that remain on the surface of green synthesized CuO NPs may reduce their toxicity effects.     

Unraveling the role of fungal symbionts in plant abiotic stress tolerance

Fungal symbionts have been found to be associated with every plant studied in the natural ecosystem, where they colonize and reside entirely or partially in the internal tissues of their host plant. Fungal endophytes can express/form a range of different lifestyle/relationships with different host including symbiotic, mutualistic, commensalistic and parasitic in response to host genotype and environmental factors. In mutualistic association fungal endophyte can enhance growth, increase reproductive success and confer biotic and abiotic stress tolerance to its host plant. Since abiotic stress such as, drought, high soil salinity, heat, cold, oxidative stress and heavy metal toxicity is the common adverse environmental conditions that affect and limit crop productivity worldwide. It may be a promising alternative strategy to exploit fungal endophytes to overcome the limitations to crop production brought by abiotic stress. There is an increasing interest in developing the potential biotechnological applications of fungal endophytes for improving plant stress tolerance and sustainable production of food crops. Here we have described the fungal symbioses, fungal symbionts and their role in abiotic stress tolerance. A putative mechanism of stress tolerance by symbionts has also been covered.Key words: abiotic stress, endophytes, fungal symbiont, mycorrhizal fungus, Piriformospora indica, stress tolerance, symbiosis     

Mitochondrial calcium transport and permeability transition as rational targets for plant protection

The mitochondrial permeability transition (MPT) is a death-inducing mechanism that collapses electrochemical gradients across inner mitochondrial membranes. Several studies in model plants have detailed potential MPT-dependent cell death upon abiotic stress in response to heat shock, ultraviolet radiation, heavy metal toxicity and waterlogging. However, the molecular specifics of the MPT and its possible role on plant cell death remain controversial. This review addresses previous and recent developments on the role(s) of the MPT in plants. Considering these advances, MPT targeting can constitute a plausible strategy to ameliorate cell death in plants upon abiotic stress.     

Managing heavy metal toxicity stress in plants: Biological and biotechnological tools

The maintenance of ion homeostasis in plant cells is a fundamental physiological requirement for sustainable plant growth, development and production. Plants exposed to high concentrations of heavy metals must respond in order to avoid the deleterious effects of heavy metal toxicity at the structural, physiological and molecular levels. Plant strategies for coping with heavy metal toxicity are genotype-specific and, at least to some extent, modulated by environmental conditions. There is considerable interest in the mechanisms underpinning plant metal tolerance, a complex process that enables plants to survive metal ion stress and adapt to maintain growth and development without exhibiting symptoms of toxicity. This review briefly summarizes some recent cell biological, molecular and proteomic findings concerning the responses of plant roots to heavy metal ions in the rhizosphere, metal ion-induced reactions at the cell wall-plasma membrane interface, and various aspects of heavy metal ion uptake and transport in plants via membrane transporters. The molecular and genetic approaches that are discussed are analyzed in the context of their potential practical applications in biotechnological approaches for engineering increased heavy metal tolerance in crops and other useful plants.     

How Plants Cope with Cadmium: Staking All on Metabolism and Gene Expression

Environmental pollullon is one of the major problems for human health. Toxic heavy metals are normally present as soil constituents or can also be spread out in the environment by human activity and agricultural techniques. Soil contamination by heavy metals as cadmium, highlights two main aspects: on one side they interfere with the life cycle of plants and therefore reduce crop yields, and on the other hand, once adsorbed and accumulated into the plant tissues, they enter the food chain poisoning animals and humans. Considering this point of view, understanding the mechanism by which plants handle heavy metal exposure, In particular cadmium stress, is a primary goal of plant-blotechnology research or plant breeders whose aim is to create plants that are able to recover high amounts of heavy metals, which can be used for phytoremediation, or identify crop varieties that do not accumulate toxic metal in grains or fruits. In this review we focus on the main symptoms of cadmium toxicity both on root apparatus and shoots. We elucidate the mechanisms that plants activate to prevent absorption or to detoxify toxic metal ions, such as synthesis of phytochelatins, metallothioneins and enzymes involved in stress response. Finally we consider new plant-biotechnology applications that can be applied for phytoremediation.     

How Plants Cope with Cadmium: Staking All on Metabolism and Gene Expression

Environmental pollullon is one of the major problems for human health. Toxic heavy metals are normally present as soil constituents or can also be spread out in the environment by human activity and agricultural techniques. Soil contamination by heavy metals as cadmium, highlights two main aspects: on one side they interfere with the life cycle of plants and therefore reduce crop yields, and on the other hand, once adsorbed and accumulated into the plant tissues, they enter the food chain poisoning animals and humans. Considering this point of view, understanding the mechanism by which plants handle heavy metal exposure, In particular cadmium stress, is a primary goal of plant-blotechnology research or plant breeders whose aim is to create plants that are able to recover high amounts of heavy metals, which can be used for phytoremediation, or identify crop varieties that do not accumulate toxic metal in grains or fruits. In this review we focus on the main symptoms of cadmium toxicity both on root apparatus and shoots. We elucidate the mechanisms that plants activate to prevent absorption or to detoxify toxic metal ions, such as synthesis of phytochelatins, metallothioneins and enzymes involved in stress response. Finally we consider new plant-biotechnology applications that can be applied for phytoremediation.     

Plant–rhizobacteria interactions alleviate abiotic stress conditions

Root-colonizing non-pathogenic bacteria can increase plant resistance to biotic and abiotic stress factors. Bacterial inoculates have been applied as biofertilizers and can increase the effectiveness of phytoremediation. Inoculating plants with non-pathogenic bacteria can provide 'bioprotection' against biotic stresses, and some root-colonizing bacteria increase tolerance against abiotic stresses such as drought, salinity and metal toxicity. Systematic identification of bacterial strains providing cross-protection against multiple stressors would be highly valuable for agricultural production in changing environmental conditions. For bacterial cross-protection to be an effective tool, a better understanding of the underlying morphological, physiological and molecular mechanisms of bacterially mediated stress tolerance, and the phenomenon of cross-protection is critical. Beneficial bacteria-mediated plant gene expression studies under non-stress conditions or during pathogenic rhizobacteria–plant interactions are plentiful, but only few molecular studies on beneficial interactions under abiotic stress situations have been reported. Thus, here we attempt an overview of current knowledge on physiological impacts and modes of action of bacterial mitigation of abiotic stress symptoms in plants. Where available, molecular data will be provided to support physiological or morphological observations. We indicate further research avenues to enable better use of cross-protection capacities of root-colonizing non-pathogenic bacteria in agricultural production systems affected by a changing climate.     

Fungal growth promotor endophytes: a pragmatic approach towards sustainable food and agriculture

Agricultural productivity suffers a heavy loss due to plant pathogens, insect pests and various abiotic stresses. Agriculture being the world’s largest economic sector, it is the need of time to find and establish the ideal strategy for sustainable agriculture and improvement in crop growth. Endophytes are microorganisms that asymptomatically grow within the plant tissues without causing any disease to the host. Endophytic fungi live in symbiotic association with plants and play an important role in plant growth promotion, higher seed yield and plants resistant to various biotic, abiotic stresses and diseases. Many are able to produce antimicrobial compounds, plant growth hormones and various agrochemical bioactive metabolites. These mycoendophytes hold enormous potential for the development of eco-friendly and economically viable agricultural products. In this review we focused on the endophytic fungi recovered from different medicinal plants, their active principles involved in plant growth enhancement and the applications of fungal endophytes in agriculture. Moreover, we also discussed about endophytic fungi and their pragmatic approach towards sustainable food and agriculture.     

Heavy Metal/Metalloid Indexing and Balances in Agricultural Soils: Methodological Approach for Research

Heavy metal(loid) accumulation in agricultural soils is a threat to the soil capacity, quality, and productivity. It also increases human exposure to heavy metal(loid)s via consumption of contaminated plant-based foods. The detrimental effects of soil contamination also deteriorate the environment of plants and animals. For sustainable agriculture, therefore, the soil must be protected from toxic levels of heavy metal(loid)s. Studies on heavy metal(loid) balances in agricultural soils are important in predicting future risks to sustainable production from agro-ecological zones and human exposure to heavy metal(loid)s. The latest and continuous indexing of the problem seems a prerequisite for sustainable agriculture. This review provides some background information and then summarizes key methodological approaches for studies on indexing and balance of heavy metal(loid)s in agricultural soils. In the end, important soil and health indices are explained that may be useful in understanding the extent of the problem. The provided information would contribute to sustainable heavy metal(loid) management in the agricultural soils, high crop production, better soil protection, and ultimately to human health.     

Seed coating with beneficial microorganisms for precision agriculture

Seed coating is a technique of covering seeds with adhesive agents to improve seed performance and plant establishment while reducing production cost. To meet the needs of development of precision agriculture, seed coating has been widely used in agriculture as an effective means to alleviate biotic and abiotic stresses, thus enhancing crop growth, yield, and health. Plant growth promoting microorganisms (PGPM) are recognized as essential contributors to improving agricultural productivity via direct application to the rhizosphere and plant tissues, or seed inoculation. However, during conventional inoculation processes, several factors such as insufficient microbial survival, hindrance in the application of biocontrol inocula to the seeds and exposure to unsuitable temperature and light in subsequent seed storage, force us to explore efficient and reliable microbial application tools. Recently, biological seed coating with PGPM is proposed as an alternative to conventional seed treatment (such as fertilizer and protection products) due to its ecological safety and socio-economic aspects. In this review, microbial seed coating technology and its contribution to sustainable precision agriculture are well discussed and highlighted in the extensive table and elaborate schematic drawings.     

Coal fly ash utilization in agriculture: its potential benefits and risks

Over the past few decades there has been avid interest in developing the strategies for the utilization of Fly ash (FA). Major foci have been on its agricultural application. It is often economical to use FA as a soil amendment. The potential of FA as a resource material in agriculture is due to its specific physical properties like’s texture, water holding capacity, bulk density, pH etc., and contains almost all the essential plant nutrients. It can be used as in soil that cannot substitute the chemical fertilizers or organic manure it can be used in combination with these to get additional benefits in terms of improvement in soil physical characteristics, increased yields etc. The amount and method of FA application in soil would vary with the type of soil, the crop, grown, the prevailing agro climatic condition and also with the FA characteristics. Although, as an input material FA has many benefits for agriculture applications like, improvement of nutrient deficiency, effectively control various pests infesting etc., in contrast FA also contains number of toxic heavy metals and also have natural radioactivity materials in it. Therefore, proper attention should be given on some important areas related to FA utilization such as long term studies of impact of FA on soil health, heavy metal uptake, plant physiology and growth, crop quality, and continuous monitoring on the soil characteristics. While using FA in agriculture problem of heavy metal toxicity and leaching due to excess dose should also be kept in mind.