Assessment of physiological and biochemical responses of Amaranthus retroflexus seedlings to the accumulation of heavy metals with regards to phytoremediation potential.

The aim of this research was to assess, under laboratory conditions, how the accumulation of four heavy metals (HMs) (lead (Pb), copper (Cu), nickel (Ni), and zinc (Zn)), prepared as aqueous solutions from 1 µM to 1 mM, affected biochemical and physiological parameters of Amaranthus retroflexus seedlings. Seedlings showed considerably high resistance to all investigated HMs and no significant oxidative stress in leaves. After chronic exposure to high doses of any of the HMs, seedlings remained viable, but with slightly slower axial growth. We propose the use of biochemical indices (lipid peroxidation (LPO) intensity; level of total peroxides) as criteria to assess the adaptive potential of amaranth plants to HMs. These indices had very high correlation coefficients (r) with the accumulation of HMs in A. retroflexus roots, stems and leaves: 0.86-0.89 for malone dialdehyde (MDA) content for Ni and Zn, and 0.79-0.94 for total peroxides (for Cu, Pb, and maximum in Ni). At 1 mM of any HM, seedlings accumulated Pb and Ni at levels of HM-hyperaccumulating species. If soil is contaminated (in terms of maximum permissible concentration, MPC) by Pb (8.2 ± 2.2 MPC) or Ni (3.5 ± 1.0 MPC) (equivalent to 1 mM of the HM in solution), A. retroflexus is a strong candidate for the phytoremediation of Pb- and Ni-contaminated soils.

Lead accumulation and distribution in maize seedlings: Relevance to biomass production and metal phytoextraction.

Among trace metals, lead is a highly toxic contaminant, being hazardous to humans and animals. Application of maize plants for phytoremediation of polluted soils and waters has recently been of particular interest. The aim of this work is to investigate the Pb-phytoextraction potential of the maize cv. Tzariza used widely in Eastern European agriculture. Maize seedlings were exposed in a nutrient solution to 1-10000 µM of Pb2+ for 21 days. Lead accumulated mostly in conductive tissues and shoots at 0.1 mM and higher concentrations of Pb in growth medium. Pb at concentrations of 1 and 10 mM caused an increase in the superoxide anion level and the catalase activity in maize leaves. Lead ions were tolerable to maize seedlings within a concentration range up to 1000 µM of Pb2+. The levels of lead in the nutrient solution above 1 mM resulted in inhibition of the growth of axial organs, decrease in leaf area, inhibition of water absorption, and reduction in accumulation of biomass. Theoretical considerations indicate that in the temperate climates of the phytoremediation with maize may allow annual removal up to 90 kg of Pb per km2, depending on the initial level of soil contamination.

Transport phenomena of nanoparticles in plants and animals/humans.

The interaction of a plethora nanoparticles with major biota such as plants and animals/humans has been the subject of various multidisciplinary studies with special emphasis on toxicity aspects. However, reports are meager on the transport phenomena of nanoparticles in the plant-animal/human system. Since plants and animals/humans are closely linked via food chain, discussion is imperative on the main processes and mechanisms underlying the transport phenomena of nanoparticles in the plant-animal/human system, which is the main objective of this paper. Based on the literature appraised herein, it is recommended to perform an exhaustive exploration of so far least explored aspects such as reproducibility, predictability, and compliance risks of nanoparticles, and insights into underlying mechanisms in context with their transport phenomenon in the plant-animal/human system. The outcomes of the suggested studies can provide important clues for fetching significant benefits of rapidly expanding nanotechnology to the plant-animal/human health-improvements and protection as well.

Nanoscale copper in the soil-plant system - toxicity and underlying potential mechanisms.

Nanoscale copper particles (nano-Cu) are used in many antimicrobial formulations and products for their antimicrobial activity. They may enter deliberately and/or accidentally into terrestrial environments including soils. Being the major 'eco-receptors' of nanoscale particles in the terrestrial ecosystem, soil-microbiota and plants (the soil-plant system) have been used as a model to dissect the potential impact of these particles on the environmental and human health. In the soil-plant system, the plant can be an indirect non-target organism of the soil-associated nano-Cu that may in turn affect plant-based products and their consumers. By all accounts, information pertaining to nano-Cu toxicity and the underlying potential mechanisms in the soil-plant system remains scanty, deficient and little discussed. Therefore, based on some recent reports from (bio)chemical, molecular and genetic studies of nano-Cu versus soil-plant system, this article: (i) overviews the status, chemistry and toxicity of nano-Cu in soil and plants, (ii) discusses critically the poorly understood potential mechanisms of nano-Cu toxicity and tolerance both in soil-microbiota and plants, and (iii) proposes future research directions. It appears from studies hitherto made that the uncontrolled generation and inefficient metabolism of reactive oxygen species through different reactions are the major factors underpinning the overall nano-Cu consequences in both the systems. However, it is not clear whether the nano-Cu or the ion released from it is the cause of the toxicity. We advocate to intensify the multi-approach studies focused at a complete characterization of the nano-Cu, its toxicity (during life cycles of the least-explored soil-microbiota and plants), and behavior in an environmentally relevant terrestrial exposure setting. Such studies may help to obtain a deeper insight into nano-Cu actions and address adequately the nano-Cu-associated safety concerns in the 'soil-plant system'.

Treatment with the herbicide TOPIK induces oxidative stress in cereal leaves.

Leaf disks as well as intact 7-day-old plants of winter wheat (Triticum aestivum L., cv. Mironovskaya 808), winter rye (Secale cereale L., cv. Estafeta Tatarstana), and maize (Zea mays L., cv. Kollektivnyi 172MV), were treated with the aryloxyphenoxypropionate class herbicide TOPIK, concentrate-emulsion (active ingredient is clodinafop-propargyl (CP), 8-800µg/L), and the effects of short-term action (up to 3h) and long-term aftereffect (up to 3days) on physiological and biochemical indices related to oxidative stress development were studied. The herbicide induced changes, predominantly increases in lipid peroxidation (LPO) intensity, superoxide anion O2(-) generation, total antioxidant activity (AOA), and catalase (CAT) and ascorbate peroxidase (APOX) activity, although the response by plants was nonlinear and depended on the herbicide concentration and duration of treatment. The highest level of generation of O2(-) was observed in the leaves of maize and winter wheat treated by 800µg/L CP, both in the short- and long-term. As TOPIK concentration increased, so too did LPO and AOA in leaves, confirming the presence of oxidative stress in the cells of all three cereals. Antioxidant enzymes were most active in winter rye and wheat, and least active in maize indicating a protective antioxidant mechanism in the first two cereals.

From Nature to Lab: A Review of Secondary Metabolite Biosynthetic Pathways, Environmental Influences, and In Vitro Approaches.

Secondary metabolites are gaining an increasing importance in various industries, such as pharmaceuticals, dyes, and food, as is the need for reliable and efficient methods of procuring these compounds. To develop sustainable and cost-effective approaches, a comprehensive understanding of the biosynthetic pathways and the factors influencing secondary metabolite production is essential. These compounds are a unique type of natural product which recognizes the oxidative damage caused by stresses, thereby activating the defence mechanism in plants. Various methods have been developed to enhance the production of secondary metabolites in plants. The elicitor-induced in vitro culture technique is considered an efficient tool for studying and improving the production of secondary metabolites in plants. In the present review, we have documented various biosynthetic pathways and the role of secondary metabolites under diverse environmental stresses. Furthermore, a practical strategy for obtaining consistent and abundant secondary metabolite production via various elicitation agents used in culturing techniques is also mentioned. By elucidating the intricate interplay of regulatory factors, this review paves the way for future advancements in sustainable and efficient production methods for high-value secondary metabolites.

Phytoremediation of Potentially Toxic Elements: Role, Status and Concerns.

Environmental contamination with a myriad of potentially toxic elements (PTEs) is triggered by various natural and anthropogenic activities. However, the industrial revolution has increased the intensity of these hazardous elements and their concentration in the environment, which, in turn, could provoke potential ecological risks. Additionally, most PTEs pose a considerable nuisance to human beings and affect soil, aquatic organisms, and even nematodes and microbes. This comprehensive review aims to: (i) introduce potentially toxic elements; (ii) overview the major sources of PTEs in the major environmental compartments; (iii) briefly highlight the major impacts of PTEs on humans, plants, aquatic life, and the health of soil; (iv) appraise the major methods for tackling PTE-caused pollution; (v) discuss the concept and applications of the major eco-technological/green approaches (comprising phytoextraction, rhizofiltration, phytostabilization, phytovolatilization, and phytorestoration); (vi) highlight the role of microbes in phytoremediation under PTE stress; and (vii) enlighten the major role of genetic engineering in advancing the phytoremediation of varied PTEs. Overall, appropriate strategies must be developed in order to stop gene flow into wild species, and biosafety issues must be properly addressed. Additionally, consistent efforts should be undertaken to tackle the major issues (e.g., risk estimation, understanding, acceptance and feasibility) in order to guarantee the successful implementation of phytoremediation programs, raise awareness of this green technology among laymen, and to strengthen networking among scientists, stakeholders, industrialists, governments and non-government organizations.

Microalgal Phycoremediation: A Glimpse into a Sustainable Environment.

Microalgae are continually exposed to heavy metals and metalloids (HMMs), which stifles their development and reproduction due to the resulting physiological and metabolic abnormalities, leading to lower crop productivity. They must thus change their way of adapting to survive in such a hostile environment without sacrificing their healthy growth, development, reproductive capacity, or survival. The mode of adaptation involves a complex relationship of signalling cascades that govern gene expression at the transcriptional and post-transcriptional levels, which consequently produces altered but adapted biochemical and physiochemical parameters. Algae have been reported to have altered their physicochemical and molecular perspectives as a result of exposure to a variety of HMMs. Hence, in this review, we focused on how microalgae alter their physicochemical and molecular characteristics as a tolerance mechanism in response to HMM-induced stress. Furthermore, physiological and biotechnological methods can be used to enhance extracellular absorption and clean up. The introduction of foreign DNA into microalgae cells and the genetic alteration of genes can boost the bio-accumulation and remediation capabilities of microalgae. In this regard, microalgae represent an excellent model organism and could be used for HMM removal in the near future.

Evaluation of cotton burdock (Arctium tomentosum Mill.) responses to multi-metal exposure.

Plants have immense potential for their use in the minimization of emerging environmental pollution issues. Under simulated laboratory conditions, this work investigated the growth and biochemical responses of 14-day-old cotton burdock (Arctium tomentosum Mill.) seedlings to the body burdens of multi-metals including Pb, Cu, Ni, and Zn (1.0 µM-10 mM). Biochemical traits (superoxide generation, lipid peroxidation, content of total peroxides), growth traits (axial organs growth, dry weight accumulation, leaf area), and also metal body burdens varied with types and concentrations of metals. Results indicated a significant tolerance of A. tomentosum to multi-metals that can be implicated for its potential role in the metal phytoremediation programs.

Catalase and ascorbate peroxidase-representative H2O2-detoxifying heme enzymes in plants.

Plants have to counteract unavoidable stress-caused anomalies such as oxidative stress to sustain their lives and serve heterotrophic organisms including humans. Among major enzymatic antioxidants, catalase (CAT; EC 1.11.1.6) and ascorbate peroxidase (APX; EC 1.11.1.11) are representative heme enzymes meant for metabolizing stress-provoked reactive oxygen species (ROS; such as H2O2) and controlling their potential impacts on cellular metabolism and functions. CAT mainly occurs in peroxisomes and catalyzes the dismutation reaction without requiring any reductant; whereas, APX has a higher affinity for H2O2 and utilizes ascorbate (AsA) as specific electron donor for the reduction of H2O2 into H2O in organelles including chloroplasts, cytosol, mitochondria, and peroxisomes. Literature is extensive on the glutathione-associated H2O2-metabolizing systems in plants. However, discussion is meager or scattered in the literature available on the biochemical and genomic characterization as well as techniques for the assays of CAT and APX and their modulation in plants under abiotic stresses. This paper aims (a) to introduce oxidative stress-causative factors and highlights their relationship with abiotic stresses in plants; (b) to overview structure, occurrence, and significance of CAT and APX in plants;

Evaluation of zinc accumulation, allocation, and tolerance in Zea mays L. seedlings: implication for zinc phytoextraction.

This work investigated the accumulation, allocation, and impact of zinc (Zn; 1.0 µM-10 mM) in maize (Zea mays L.) seedlings under simulated laboratory conditions. Z. mays exhibited no significant change in its habitus (the physical characteristics of plants) up to 10-1000 µM of Zn (vs 5-10 mM Zn). Zn tolerance evaluation, based on the root test, indicated a high tolerance of Z. mays to both low and intermediate (or relatively high) concentrations of Zn, whereas this plant failed to tolerate 10 mM Zn and exhibited a 5-fold decrease in its Zn tolerance. Contingent to Zn treatment levels, Zn hampered the growth of axial organs and brought decreases in the leaf area, water regime, and biomass accumulation. Nevertheless, at elevated levels of Zn (10 mM), Zn(2+) was stored in the root cytoplasm and inhibited both axial organ growth and water regime. However, accumulation and allocation of Zn in Z. mays roots, studied herein employing X-ray fluorimeter and histochemical methods, were close to Zn accumulator plants. Overall, the study outcomes revealed Zn tolerance of Z. mays, and also implicate its potential role in Zn phytoextraction.

Lipids and proteins--major targets of oxidative modifications in abiotic stressed plants.

Stress factors provoke enhanced production of reactive oxygen species (ROS) in plants. ROS that escape antioxidant-mediated scavenging/detoxification react with biomolecules such as cellular lipids and proteins and cause irreversible damage to the structure of these molecules, initiate their oxidation, and subsequently inactivate key cellular functions. The lipid- and protein-oxidation products are considered as the significant oxidative stress biomarkers in stressed plants. Also, there exists an abundance of information on the abiotic stress-mediated elevations in the generation of ROS, and the modulation of lipid and protein oxidation in abiotic stressed plants. However, the available literature reflects a wide information gap on the mechanisms underlying lipid- and protein-oxidation processes, major techniques for the determination of lipid- and protein-oxidation products, and on critical cross-talks among these aspects. Based on recent reports, this article (a) introduces ROS and highlights their relationship with abiotic stress-caused consequences in crop plants, (b) examines critically the various physiological/biochemical aspects of oxidative damage to lipids (membrane lipids) and proteins in stressed crop plants, (c) summarizes the principles of current technologies used to evaluate the extent of lipid and protein oxidation, (d) synthesizes major outcomes of studies on lipid and protein oxidation in plants under abiotic stress, and finally, (e) considers a brief cross-talk on the ROS-accrued lipid and protein oxidation, pointing to the aspects unexplored so far.