Effects of Antimony Stress on Growth and Physiology of 10 Genotypes of Catalpa bungei

Increasing levels of antimony (Sb) pollution have been recognized as an emerging environmental problem. Phytoremediation of Sb-contaminated soil is a green, economical, and effective method for restoring polluted soils. Here, we studied differences in Sb tolerance, accumulation, and transport by different genotypes of Catalpa bungei C. A. Mey, with the goal of identifying genotypes that are suitable for remediating Sb-contaminated soil. Different concentrations of Sb were applied to soil, and we analyzed variation in growth, biomass, Sb content in different organs, Sb transport capacity, oxidizing substances, antioxidants, and antioxidant enzyme activities in 10 C. bungei genotypes. Marked differences were found in plant height, ground diameter, and biomass among different genotypes at given Sb concentrations. The Sb concentration in different plant organs also varied between genotypes. The content of Sb in each genotype was proportional to the exposure. At 600 mg Sb/kg soil, the highest concentration of Sb in roots and leaves was found in Genotype 63, and that in stems was found in Genotype 8402. The lowest concentration of Sb in roots, stems, and leaves was found in Genotypes 8402, 2-8, and 20-01, respectively. At 1200 mg Sb/kg soil, Genotype 5-2 had the highest concentration of Sb in roots, and Genotype 1-1 had the highest concentration in stems and leaves. The lowest concentration of Sb in roots was in Genotype 72, and that in stems and leaves was found in Genotype 20-01. At 2000 mg Sb/kg soil, the highest concentration of Sb in roots was found in Genotype 5-8, in stems in Genotype 8402, and in leaves in Genotype 72. The lowest concentration of Sb in roots was observed in Genotype 72 and in stems and leaves in Genotype 2-8. After absorption by C. bungei, Sb mainly accumulated in the roots, and upward transfer ability was poor. The Sb biological concentration factor of roots of all genotypes was >1 at each tested Sb concentration. Our results demonstrate that all 10 C. bungei genotypes could be used for plant stabilization of Sb-contaminated soil. However, the different genotypes of C. bungei had different responses to different Sb concentrations. Based on root Sb accumulation values, at soil Sb concentrations around 600 mg/kg, Genotypes 1, 63, and 5-8 are suited to phytoremediation; Genotypes 5-8, 1, and 5-2 are suited to phytoremediation at soil Sb concentrations around 1200 mg/kg; and Genotypes 5-8, 1, and 8402 are suited to phytoremediation at soil Sb concentrations around 2000 mg/kg. We demonstrate for the first time that Sb-contaminated soil can be improved by using specific plant genotypes tailored to different levels of Sb pollution.

Overexpression of BnPCS1, a Novel Phytochelatin Synthase Gene From Ramie (Boehmeria nivea), Enhanced Cd Tolerance, Accumulation, and Translocation in Arabidopsis thaliana

Phytochelatins (PCs) play important roles in the detoxification of and tolerance to heavy metals in plants. The synthesis of PCs is catalyzed by phytochelatin synthase (PCS), which is activated by heavy metal ions. In this study, we isolated a PCS gene, BnPCS1, from the bast fiber crop ramie (Boehmeria nivea) using the RACE (rapid amplification of cDNA ends) method. The full-length BnPCS1 cDNA is 1,949 bp in length with a 1,518 bp open reading frame (ORF) that encodes a 505 amino acid protein. The deduced BnPCS1 protein has a conserved N-terminus containing the catalytic triad Cys58, His164, Asp182, and a flexible C-terminal region containing a C371C372QETC376VKC379 motif. The BnPCS1 promoter region contains several cis-acting elements involved in phytohormone or abiotic stress responses. Subcellular localization analysis indicates that the BnPCS1-GFP protein localizes to the nucleus and the cytoplasm. Real-time PCR assays show that the expression of BnPCS1 is significantly induced by cadmium (Cd) and the plant hormone abscisic acid (ABA). Overexpression lines of BnPCS1 exhibited better root growth and fresh weight, lower level of MDA and H2O2, and higher Cd accumulation and translocation factor compared to the WT under Cd stress. Taken together, these results could provide new gene resources for phytoremediation of Cd-contaminated soils.

Synthetic biology approaches to copper remediation: bioleaching, accumulation, and recycling

One of the current aims of synthetic biology is the development of novel microorganisms that can mine economically important elements from the environment or remediate toxic waste compounds. Copper, in particular, is a high-priority target for bioremediation owing to its extensive use in the food, metal, and electronic industries and its resulting common presence as an environmental pollutant. Even though microbe-aided copper biomining is a mature technology, its application to waste treatment and remediation of contaminated sites still requires further research and development. Crucially, any engineered copper-remediating chassis must survive in copper-rich environments and adapt to copper toxicity; they also require bespoke adaptations to specifically extract copper and safely accumulate it as a human-recoverable deposit to enable biorecycling. Here, we review current strategies in copper bioremediation, biomining, and biorecycling, as well as strategies that extant bacteria use to enhance copper tolerance, accumulation and mineralization in the native environment. By describing the existing toolbox of copper homeostasis proteins from naturally occurring bacteria, we show how these modular systems can be exploited through synthetic biology to enhance the properties of engineered microbes for biotechnological copper recovery applications.

Pharmacological Chaperones Attenuate the Development of Opioid Tolerance

Opioids are potent analgesics widely used to control acute and chronic pain, but long-term use induces tolerance that reduces their effectiveness. Opioids such as morphine bind to mu opioid receptors (MORs), and several downstream signaling pathways are capable of inducing tolerance. We previously reported that signaling from the endoplasmic reticulum (ER) contributed to the development of morphine tolerance. Accumulation of misfolded proteins in the ER induced the unfolded protein response (UPR) that causes diverse pathological conditions. We examined the effects of pharmacological chaperones that alleviate ER stress on opioid tolerance development by assessing thermal nociception in mice. Pharmacological chaperones such as tauroursodeoxycholic acid and 4-phenylbutyrate suppressed the development of morphine tolerance and restored analgesia. Chaperones alone did not cause analgesia. Although morphine administration induced analgesia when glycogen synthase kinase 3β (GSK3β) was in an inactive state due to serine 9 phosphorylation, repeated morphine administration suppressed this phosphorylation event. Co-administration of chaperones maintained the inactive state of GSK3β. These results suggest that ER stress may facilitate morphine tolerance due to intracellular crosstalk between the UPR and MOR signaling. Pharmacological chaperones may be useful in the management of opioid misuse.

Mechanisms of Copper Tolerance, Accumulation, and Detoxification in the Marine Macroalga Ulva compressa (Chlorophyta): 20 Years of Research

Copper induces an oxidative stress condition in the marine alga Ulva compressa that is due to the production of superoxide anions and hydrogen peroxide, mainly in organelles. The increase in hydrogen peroxide is accompanied by increases in intracellular calcium and nitric oxide, and there is a crosstalk among these signals. The increase in intracellular calcium activates signaling pathways involving Calmodulin-dependent Protein Kinases (CaMKs) and Calcium-Dependent Protein Kinases (CDPKs), leading to activation of gene expression of antioxidant enzymes and enzymes involved in ascorbate (ASC) and glutathione (GSH) synthesis. It was recently shown that copper also activates Mitogen-Activated Protein Kinases (MAPKs) that participate in the increase in the expression of antioxidant enzymes. The increase in gene expression leads to enhanced activities of antioxidant enzymes and to enhanced levels of ASC and GSH. In addition, copper induces an increase in photosynthesis leading to an increase in the leve of Nicotinamide Adenine Dinucleotide Phosphate (NADPH). Copper also induces an increase in activities of enzymes involved in C, N, and S assimilation, allowing the replacement of proteins damaged by oxidative stress. The accumulation of copper in acute exposure involved increases in GSH, phytochelatins (PCs), and metallothioneins (MTs) whereas the accumulation of copper in chronic exposure involved only MTs. Acute and chronic copper exposure induced the accumulation of copper-containing particles in chloroplasts. On the other hand, copper is extruded from the alga with an equimolar amount of GSH. Thus, the increases in activities of antioxidant enzymes, in ASC, GSH, and NADPH levels, and in C, N, and S assimilation, the accumulation of copper-containing particles in chloroplasts, and the extrusion of copper ions from the alga constitute essential mechanisms that participate in the buffering of copper-induced oxidative stress in U. compressa.

Greenhouse assessment of citric acid-assisted phytoremediation of cadmium by willows (Salix spp.) - effect on photosynthetic performances and metal tolerance

The aim of this study was to define effects of cadmium (Cd) applied alone and in combination with citric acid, on the plant tolerance, accumulation, translocation and photosynthesis in willows (Salix viminalis, S. matsudana and S. alba). Low metal bioavailability in soil is often the limiting factor for phytoextraction, thus citric acid was used as a chelating agent aiming to improve metal solubility and therefore accelerates phytoextraction. Willows were grown by soil culture method in semi-controlled conditions (greenhouse) with two different Cd concentrations (3 and 6 ppm), applied separately and in combination with citric acid (20 mM/kg of dry soil), followed by control plants. The reduction of plant growth, biomass, photosynthesis parameters, chlorophyll and carotenoids were induced by Cd supplied. The addition of citric acid showed beneficial effects on different morpho-physiological levels through alleviate stress conditions as well as enhancing overall phytoextraction. Citric acid (CA) has increased transport of the accumulated Cd from the roots to aerial part in S.viminalis and S.alba in comparison with same treatments without CA, as well as tolerance of analyzed clones. Significant depressive effect on photosynthetic CO2 assimilation was evident in plants grown in soil with Cd applied. A significant negative correlation between biomass production, leaf area, and photosynthesis due to the presence of Cd in plant tissue was observed in S. viminalis. Bioaccumulation factor among selected willow clones was higher than 1, reliably suggesting good potential of selected genotypes for phytoextraction. Key words: willows, cadmium, citric acid, soil phytoextraction, photosynthesis, accumulation, translocation, tolerance