Effect of Cd 2+ and Cd 2+ /auxin mixtures on lipid monolayers – Model membrane studies on the role of auxins in phytoremediation of metal ions from contaminated environment

The Complexity of the Influence of Growth Substances, Heavy Metals, and Their Combination on the Volume Dynamics of Vacuoles Isolated from Red Beet (Beta vulgaris L.) Taproot Cells

The plant vacuole is a very dynamic organelle that can occupy more than 90% of the cell volume and is essential to plant cell growth and development, the processes in which auxin (indole-3-acetic acid, IAA) is a central player. It was found that when IAA or FC (fusicoccin) was present in the control medium of vacuoles isolated from red beet taproots at a final concentration of 1 µM, it increased their volume to a level that was 26% or 36% higher than that observed in the control medium without growth regulators, respectively. In the presence of IAA and FC, the time after which most vacuoles ruptured was about 10 min longer for IAA than for FC. However, when cadmium (Cd) or lead (Pb) was present in the control medium at a final concentration of 100 µM, it increased the volume of the vacuoles by about 26% or 80% compared to the control, respectively. The time after which the vacuoles ruptured was similar for both metals. The combined effect of IAA and Pb on the volume of the vacuoles was comparable with that observed in the presence of Pb only, while for FC combined with Pb, it was additive. The use of IAA or FC together with Cd caused in both cases a decrease in the vacuole volumes by about 50%. The data presented in this study are discussed, taking into account the structure and function of the vacuolar membrane (tonoplast) and their changes in the presence of growth substances, heavy metals, and their combination.

Auxin homeostasis in plant responses to heavy metal stress

Expeditious industrialization and anthropogenic activities have resulted in large amounts of heavy metals (HMs) being released into the environment. These HMs affect crop yields and directly threaten global food security. Therefore, significant efforts have been made to control the toxic effects of HMs on crops. When HMs are taken up by plants, various mechanisms are stimulated to alleviate HM stress, including the biosynthesis and transport of auxin in the plant. Interestingly, researchers have noted the significant potential of auxin in mediating resistance to HM stress, primarily by reducing uptake of metals, promoting chelation and sequestration in plant tissues, and mitigating oxidative damage. Both exogenous administration of auxin and manipulation of intrinsic auxin status are effective strategies to protect plants from the negative consequences of HMs stress. Regulation of genes and transcription factors related to auxin homeostasis has been shown to be related to varying degrees to the type and concentration of HMs. Therefore, to derive the maximum benefit from auxin-mediated mechanisms to attenuate HM toxicities, it is essential to gain a comprehensive understanding of signaling pathways involved in regulatory actions. This review primarily emphases on the auxin-mediated mechanisms participating in the injurious effects of HMs in plants. Thus, it will pave the way to understanding the mechanism of auxin homeostasis in regulating HM tolerance in plants and become a tool for developing sustainable strategies for agricultural growth in the future.

Phytoremediation as a potential technique for vehicle hazardous pollutants around highways

With the synchronous development of highway construction and the urban economy, automobiles have entered thousands of households as essential means of transportation. This paper reviews the latest research progress in using phytoremediation technology to remediate the environmental pollution caused by automobile exhaust in recent years, including the prospects for stereoscopic forestry. Currently, most automobiles on the global market are internal combustion vehicles using fossil energy sources as the primary fuel, such as gasoline, diesel, and liquid or compressed natural gas. The composition of vehicle exhaust is relatively complex. When it enters the atmosphere, it is prone to a series of chemical reactions to generate various secondary pollutants, which are very harmful to human beings, plants, animals, and the eco-environment. Despite improving the automobile fuel quality and installing exhaust gas purification devices, helping to reduce air pollution, the treatment costs of these approaches are expensive and cannot achieve zero emissions of automobile exhaust pollutants. The purification of vehicle exhaust by plants is a crucial way to remediate the environmental pollution caused by automobile exhaust and improve the environment along the highway by utilizing the ecosystem's self-regulating ability. Therefore, it has become a global trend to use phytoremediation technology to restore the automobile exhaust pollution. Now, there is no scientific report or systematic review about how plants absorb vehicle pollutants. The screening and configuration of suitable plant species is the most crucial aspect of successful phytoremediation. The mechanisms of plant adsorption, metabolism, and detoxification are reviewed in this paper to address the problem of automobile exhaust pollution.

Shifts of lipid metabolites help decode immobilization of soil cadmium under reductive soil disinfestation

Cadmium (Cd) contamination in soil can cause serious environmental problems and threaten human health. Previous studies have shown that the reductive soil disinfestation (RSD) is regarded as an effective soil disinfection technology, which will affect the bioavailability of Cd. However, the influence of soil microorganisms and their metabolites on the morphologies of Cd during RSD treatment are still poorly understood. Here, a laboratory incubation experiment that composed of untreated soil (CK), two RSD treatments with flooded soil (FL) and added 2% bean dregs soil (BD) was conducted. After the treatment, the content of different morphologies of Cd in the soil and the molecular characteristics (the composition of the microbial community, functional enzymes and metabolites) of the soil were measured. The study found that, compared to CK treatment, the dominant phyla, such as Acidobacteria, Bacteroidetes, Firmicutes, etc., were significantly increased in BD treatment, and enzymes related to metabolism also showed noticeable enhancement. The differential accumulated metabolite (DAM) analysis revealed that the abound of lipids and lipid-like molecules involved with fatty acyls, steroids and steroid derivatives, glycerophospholipids, fatty acids and conjugates, glycerolipids, and sphingolipids were significant different among treatments. The correlation analysis showed the exchangeable fraction cadmium contents (EX-Cd) were negatively correlated with the content of glycerophospholipids and sphingolipids, and positively correlated with glycerolipids content. However, the relationship between the residual cadmium (RS-Cd) and these three metabolites was just the opposite. Compared with another two treatments, the BD treatment significantly reduced EX-Cd contents. Biological interaction network analysis indicated that the phyla Gemmatimonadetes and Proteobacteria assumed the primary responsibility for the morphological transformation of Cd through their corresponding functional enzymes. Overall, this study provided a new perspective on RSD-mediated soil Cd immobilization, and the findings should be beneficial to further applications of RSD technology on the remediation of Cd-polluted soils.

Interactions of l-arginine with Langmuir monolayers of common phospholipids at the air-water interface

The interactions of l-arginine (l-arg) with Langmuir monolayers of three most common phospholipids, which are sodium salt of dipalmitoylphosphatidylglycerol (DPPG), dipalmitoylphosphatidylcholine (DPPC) and dipalmitoylphosphatidylethanolamine (DPPE), have been investigated at the air-water interface. The surface pressure-area (π-A) isotherms of these monolayers have been measured with a film balance and monolayer morphology has been observed by a Brewster angle microscopy (BAM). The DPPG monolayers on pure water do not show any phase transition but show irregular shaped condensed phases formed just after evaporation of the solvent at 20 °C. However, this monolayer on l-arg solution subphase indicates a first-order phase transition from liquid expanded to liquid condensed (LE-LC) phases and forms LC domains at the same temperature. With an increase in the l-arg concentration in the subphase up to 5.0 × 10^-4 M, the π-A shows an overall increasingly greater expansion in the molecular area. All of the π-A isotherms recorded on ≥5.0 × 10^-4 M l-arg solution subphases almost coincide with each other. These changes in the phase behavior have been explained by the fact that l-arg having guanidinium cationic group undergoes strong hydrogen bonding interaction with the anionic phosphatidylglycerol (PG-) head group. The bonding between two molecules is further strengthened by electrostatic attraction between cationic l-arg and anionic PG- ions. The BAM observation of the monolayer morphology supports this explanation. On the other hand, a very negligible interaction has been observed between l-arg and DPPC or DPPE monolayers. The π-A isotherms in the presence of l-arg for both the amphiphiles show a very little expansion only in the LE phase region, but coincide in the so called solid phase region. The monolayer morphology of both the monolayers also supports these results. This little effect of expansion in the LE region may be explained by the ion-pair formation between cationic l-arg and anionic head groups in the monolayers at lower pressures. However, due to compression at high pressure, the l-arg molecules are squeezed out from the amphiphile head groups.

Phytoremediation of Heavy Metal Pollution: A Bibliometric and Scientometric Analysis from 1989 to 2018

This paper aims to evaluate the knowledge landscape of the phytoremediation of heavy metals (HMs) by constructing a series of scientific maps and exploring the research hotspots and trends of this field. This study presents a review of 6873 documents published about phytoremediation of HMs in the international context from the Web of Science Core Collection (WoSCC) (1989–2018). Two different processing software applications were used, CiteSpace and Bibliometrix. This research field is characterized by high interdisciplinarity and a rapid increase in the subject categories of engineering applications. The basic supporting categories mainly included “Environmental Sciences & Ecology”, “Plant Sciences”, and “Agriculture”. In addition, there has been a trend in recent years to focus on categories such as “Engineering, Multidisciplinary”, “Engineering, Chemical”, and “Green & Sustainable Science & Technology”. “Soil”, “hyperaccumulator”, “enrichment mechanism/process”, and “enhance technology” were found to be the main research hotspots. “Wastewater”, “field crops”, “genetically engineered microbes/plants”, and “agromining” may be the main research trends. Bibliometric and scientometric analysis are useful methods to qualitatively and quantitatively measure research hotspots and trends in phytoremediation of HM, and can be widely used to help new researchers to review the available research in a certain research field.

Exploring the membrane toxicity of decabromodiphenyl ethane (DBDPE): Based on cell membranes and lipid membranes model

Decabromodiphenyl ethane (DBDPE) is widely used in industry as an alternative to the decabromodiphenyl ether (BDEs). The large-scale use of DBDPE could lead to rapid growth of the human accumulation level of DBDPE. However, the biophysics of accumulation of DBDPE in cell membranes, as one of determinants of DBDPE metabolism is not clear. In the present study, detailed observations of cell lactate dehydrogenase (LDH) and reactive oxygen species (ROS) levels measurements proved that the DBDPE exposure to cell could result in significant cell membrane damage by concentration-dependent manners. The fluorescence anisotropy analysis supported the evidence that high concentration DBDPE bound decreased membrane fluidity significantly. Besides it, a detailed molecular dynamic (MD) simulation was approached to investigate the effects of DBDPE on the DPPC (dipalmitoyl phosphatidylcholine) phospholipid bilayer, which was constructed as the model of cell membrane. The molecular dynamic simulation revealed that DBDPE molecules can easily enter the membrane from the aqueous phase. Under the concentration of a threshold, the DBDPE molecules tended to aggregate inside the DPPC bilayer and caused pore formation. The bound of high concentration of DBDPE could result in significant variations in DPPC bilayer with a less dense, more disorder and rougher layer. The knowledge about DBDPEs interactions with lipid membranes is fundamentally essential to understand the in vivo process of DBDPE and the physical basis for the toxicity of DBDPE in cell membranes.

The interaction of trace heavy metal with lipid monolayer in the sea surface microlayer

Lipid molecules and trace heavy metals are enriched in sea surface microlayer and can be transferred into the sea spray aerosol. To better understand their impact on marine aerosol generation and evolution, we investigated the interaction of trace heavy metals including Fe³⁺, Pb²⁺, Zn²⁺, Cu²⁺, Ni²⁺, Cr³⁺, Cd²⁺, and Co²⁺, with dipalmitoylphosphatidylcholine (DPPC) monolayers at the air-water interface. Phase behavior of the DPPC monolayer on heavy metal solutions was probed with surface pressure-area (π-A) isotherms. The conformation order and orientation of DPPC alkyl chains were characterized by infrared reflection-absorption spectroscopy (IRRAS). The π-A isotherms show that Zn²⁺ and Fe³⁺ strongly interact with DPPC molecules, and induce condensation of the monolayers in a concentration-dependent manner. IRRAS spectra show that the formation of cation-DPPC complex gives rise to conformational changes and immobilization of the headgroups. The current results suggest that the enrichment of Zn²⁺ in sea spray aerosols is due to strong binding to the DPPC film. The interaction of Fe³⁺ with DPPC monolayers can significantly influence their surface organizations through the formation of lipid-coated particles. These results suggest that the sea surface microlayer is capable of accumulating much higher amounts of these metals than the subsurface water. The organic and metal pollutants may transfer into the atmosphere by this interaction.