Net Cd Research Articles

R-Napropamide Potentially Regulates Cadmium Accumulation in Arabidopsis Shoots through Transport Channel Modulation.

Heavy metal contamination in soils poses a significant environmental threat to human health. This study examines the effects of the chiral herbicide napropamide (NAP) on Arabidopsis thaliana, focusing on growth metrics and cadmium (Cd) accumulation. R-NAP does not adversely affect plant growth compared to the control, whereas S-NAP significantly reduces root length and fresh weight. Notably, R-NAP markedly increases Cd accumulation in the shoots, exceeding levels observed in the control and S-NAP. This increase coincides with reduced photosynthetic efficiency. Noninvasive electrode techniques reveal a higher net Cd absorption flux in the root mature zone under R-NAP than S-NAP, although similar to the control. Transcriptomic analysis highlights significant stereoisomer differences in Cd transporters, predominantly under R-NAP treatment. SEM and molecular docking simulations support that R-NAP primarily upregulates transporters such as HMA4. The results suggest careful management of herbicides like R-NAP in contaminated fields to avoid excessive heavy metal buildup in crops.

Cadmium accumulation in soil resulting from application of biogas digestate and wood ash – Mass balance modelling

This study investigates the impact of substituting conventional NPK fertilizer with wood ash and biogas digestates at an agricultural field site in southwest Sweden. A three-year field experiment, comprising a crop rotation cycle of spring wheat, winter wheat, and oats, was conducted. The obtained results were employed to establish a dynamic mass balance model for the A horizon of the soil at the site. The Cd leaching term in the model was estimated using the Stockholm Humic model (SHM), which was recalibrated to accommodate low Cd concentrations by incorporating Cd complexation to thiol sites. The findings indicate that treatments receiving NPK fertilizer and biogas digestates experienced a net Cd loss, whereas treatments with wood ash demonstrated net Cd accumulation, attributed to its higher Cd content. Harvest yields were highest in the NPK treatment, and lower in two of the wood ash treatments, likely due to lower nitrogen additions in the latter. Cd offtake mirrored this trend, with the highest values in the NPK treatments and the lowest in the wood ash treatments, potentially also influenced by a pH difference of 0.2 units during the last year of the experiment. Geochemical modelling showed that Cd leaching is highly dependent on pH and that geochemically active soil Cd in the A horizon may have doubled between 1950 and 2002, due to elevated atmospheric deposition and fertilizer Cd during this period. Despite significant reductions in anthropogenic Cd fluxes since 2002, soil Cd has only decreased by 4%, showing the slow response of the soil pool to flux changes. Attaining a new steady-state after alterations in input fluxes will require hundreds of years. These results carry significance for determining sustainable application rates for recycled nutrient sources and underscore the crucial role of pH-dependent Cd sorption for Cd leaching.

Sly-miR398 Participates in Cadmium Stress Acclimation by Regulating Antioxidant System and Cadmium Transport in Tomato (Solanum lycopersicum).

Cadmium (Cd) pollution is one of the major threats in agricultural production, and can cause oxidative damage and growth limitation in plants. MicroRNA398 (miR398) is involved in plant resistance to different stresses, and the post-transcriptional regulation of miR398 on CSDs plays a key role. Here, we report that miR398 was down-regulated in tomato in response to Cd stress. Simultaneously, CSD1 and SOD were up-regulated, with CSD2 unchanged, suggesting CSD1 is involved in miR398-induced regulation under Cd stress. In addition, the role of miR398 in Cd tolerance in tomato was evaluated using a transgenic line overexpressing MIR398 (miR398#OE) in which the down-expression of miR398 was disrupted. The results showed that Cd stress induced more significant growth inhibition, oxidative damage, and antioxidant enzymes disorder in miR398#OE than that in wild type (WT). Moreover, higher Cd concentration in the shoot and xylem sap, and net Cd influx rate, were observed in miR398#OE, which could be due to the increased Cd uptake genes (IRT1, IRT2, and NRAMP2) and decreased Cd compartmentalization gene HMA3. Overall, our results indicate that down-regulated miR398 plays a protective role in tomato against Cd stress by modulating the activity of antioxidant enzymes and Cd uptake and translocation.

Plant cadmium resistance 6 from Salix linearistipularis (SlPCR6) affects cadmium and copper uptake in roots of transgenic Populus

Phytoextraction in phytoremediation is one of the environmentally friendly methods used for restoring soils contaminated by heavy metals (HMs). The screening and identification of HM-resistant plants and their regulatory genes associated with HM ion transport are the key research aims in this field. In this study, a plant cadmium (Cd) resistance (PCR) gene family member, SlPCR6, was identified in roots of Salix linearistipularis, which exhibits strong HM resistance. The results revealed that SlPCR6 expression was induced in S. linearistipularis roots in response to Cd stress. Furthermore, SlPCR6 was mainly localized on the plasma membrane. Compared with the wild type, SlPCR6 overexpression reduced the Cd and copper (Cu) contents in the transgenic poplar (84 K) and increased its Cd and Cu resistance. The roots of transgenic poplar seedlings had lower net Cd and Cu uptake rates than wild type roots. Further investigation revealed that the transcript levels of multiple HM ion transporters were not significantly different between the roots of the wild type and those of the transgenic poplar. These results suggest that SlPCR6 is directly involved in Cd and Cu transport in S. linearistipularis roots. Therefore, SlPCR6 can serve as a candidate gene to improve the phytoextraction of the HMs Cd and Cu through genetic engineering.

Annual net input fluxes of cadmium in paddy soils in karst and non-karst areas of Guangxi, China

In recent years, the problems of high cadmium content and low Cd mobility in karst areas compared with non-karst areas have attracted extensive attention. Identifying the difference between the net Cd flux in karst and non-karst areas is crucial for sustainable land management. Basically, rock weathering is a natural source of Cd. While Cd accumulation in soil has increased due to both anthropogenic and natural sources, the contributions of anthropogenic input and rock weathering to soil Cd concentration in karst and non-karst areas remain unclear. In this study, the input (e.g., atmospheric deposition, fertilizer and irrigation) and output fluxes (e.g., leaching and early and later rice harvest) of Cd in farmland soils in karst and non-karst areas of Guangxi from 2017 to 2018 were monitored. The results showed no significant difference (P = 0.289) in the contributions of various input pathways between karst area and non-karst area, and atmospheric deposition (64–55 %) played an important role in the input fluxes. Nevertheless, the low soil pH value and high rainfall in non-karst areas increase Cd mobility and plant availability in soil, causing the output flux in non-karst areas (5.30 g/ha/y) to be greater than that in karst areas (3.17 g/ha/y). According to the national standard, the exceedance rate of Cd in rice grains in non-karst area (17 %) was higher than that in karst area (15 %). Therefore, ecological risk assessment in non-karst areas with high Cd bioavailability should be prioritized. Furthermore, the annual increase rate of Cd concentration in topsoil of karst and non-karst areas was −0.27 μg/kg/y and −1.23 μg/kg/y, respectively. However, the soil Cd concentration in karst and some non-karst areas still exceeded the guideline value. Given that the net input flux of Cd was negative, the accumulation of Cd in soil may be determined by rock weathering.

Graphene oxide decreases Cd concentration in rice seedlings but intensifies growth restriction

The extensive use of graphene oxide (GO) results in its inevitable entry into the environment, raising risks to the environment, especially the ecological risks when coexisting with other contaminants. Nevertheless, how GO affects the biological behavior of Cd in plants remains poorly understood. Here, we report that the transcript levels of Cd transporters, including OsIRT1, OsIRT2, OsNramp1, OsNramp5, and OsHMA2, were decreased by 56–96% in Cd-stressed rice seedlings with exposure to 400 mg L−1 GO compared with those without GO exposure. The in situ non-invasive microelectrodes test revealed that GO clearly reduced the net Cd influx of rice roots. Thus, GO exposure decreased the level of Cd in rice seedlings by approximately 60%, compared with the GO-free condition. However, the analyses of biomass, chlorophyll fluorescence parameters and Evans blue staining, indicated that GO had adverse effects on the robustness of plants under the Cd co-contaminated condition. Taken together, although GO reduced the accumulation of Cd in rice seedlings, it still negatively affected plant growth. Therefore, the positive and negative impacts of GO on crop production are of concern. Our findings provide new information for establishing a wider phytotoxicity evaluation system for the safe manufacture and use of GO.

Calcium-Dependent Hydrogen Peroxide Mediates Hydrogen-Rich Water-Reduced Cadmium Uptake in Plant Roots.

Hydrogen gas (H2) has a possible signaling role in many developmental and adaptive plant responses, including mitigating the harmful effects of cadmium (Cd) uptake from soil. We used electrophysiological and molecular approaches to understand how H2 ameliorates Cd toxicity in pak choi (Brassica campestrisssp. chinensis). Exposure of pak choi roots to Cd resulted in a rapid increase in the intracellular H2 production. Exogenous application of hydrogen-rich water (HRW) resulted in a Cd-tolerant phenotype, with reduced net Cd uptake and accumulation. We showed that this is dependent upon the transport of calcium ions (Ca2+) across the plasma membrane and apoplastic generation of hydrogen peroxide (H2O2) by respiratory burst oxidase homolog (BcRbohD). The reduction in root Cd uptake was associated with the application of exogenous HRW or H2O2 This reduction was abolished in the iron-regulated transporter1 (Atirt1) mutant of Arabidopsis (Arabidopsis thaliana), and pak choi pretreated with HRW showed decreased BcIRT1 transcript levels. Roots exposed to HRW had rapid Ca2+ influx, and Cd-induced Ca2+ leakage was alleviated. Two Ca2+ channel blockers, gadolinium ion (Gd3+) and lanthanum ion (La3+), eliminated the HRW-induced increase in BcRbohD expression, H2O2 production, and Cd2+ influx inhibition. Collectively, our results suggest that the Cd-protective effect of H2 in plants may be explained by its control of the plasma membrane-based NADPH oxidase encoded by RbohD, which operates upstream of IRT1 and regulates root Cd uptake at both the transcriptional and functional levels. These findings provide a mechanistic explanation for the alleviatory role of H2 in Cd accumulation and toxicity in plants.

Non-invasive microelectrode cadmium flux measurements reveal the decrease of cadmium uptake by zinc supply in pakchoi root (Brassica chinensis L.)

Zinc (Zn) possesses similar properties to cadmium (Cd) and inhibits Cd uptake in plants. To get more detailed mechanisms of Zn-inhibited Cd uptake in pakchoi, a hydroponic experiment was conducted to investigate the effects of various Zn levels on Cd concentrations, real time flux of Cd, expressions of genes related to Cd uptake under Cd exposure. The results showed that the Cd concentrations and Cd accumulations in pakchoi root decreased with increasing Zn levels, which were coincident with that real time Cd influx and net Cd influx of pakchoi root decreased with increasing Zn levels by non-invasive micro-test technology (NMT). Additionally, the expressions of Cd-related transporters including BcNRAMP5, BcIRT1 and BcMGT1 decreased with the increase of Zn levels under Cd exposure, especially BcIRT1 with the highest decreased rates. Furthermore, the expressions of these genes decreased gradually with the prolongation of Zn treated time under Cd toxicity. The results indicate that Zn inhibits Cd uptake by inhibition of the expressions of Cd-related transporters, especially BcIRT1 in pakchoi root.

Direct and indirect charged aerodynamic mechanisms in the ionosphere

Objects in a flowing plasma may exchange momentum both directly, through gas-surface interactions, and indirectly, through field effects. Applying a control surface approach developed in the study of dusty (complex) plasmas, this work outlines a framework for investigating the relative contribution of direct and indirect charged aerodynamic forces that may arise from the aerodynamic interaction of LEO objects with the ionosphere i.e. ionospheric aerodynamics. In particular, this work focuses on plasma interaction phenomena described by the scaling parameters αk and χ, which describe the ratio of body potential energy to ion kinetic energy and the ratio of body size to sheath thickness respectively. Ion kinetic dominated flows (αk≪1) were found to be well approximated by neutral aerodynamic treatments, the charged drag coefficient (CD,C) of a long (2D) cylinder with a diffusely reflecting surface with complete thermal accommodation to a 500 K wall calculated as 2.232. Body potential dominated systems (αk≫1), however, were dominated by indirect charged aerodynamic mechanisms, an example being the indirect thrust required to balance the sheath driven acceleration of ions through the fore-body sheath, which caused an 82% reduction in net charged drag for the αk=16.9 case. This drag reduction was partially offset by indirect drag forces caused by the deflection of non-colliding ions, the net CD,C being 7.741 for the αk=16.9. A similar study of the relative sheath thickness, described by χ, saw asymptotic behaviours given a constant αk of 1.072; direct charged drag forces becoming either Orbital Motion Limit (OML) for thick-sheath systems (χ→0) or sheath-limited (χ≫1). These results demonstrate the importance of accounting for both direct and indirect charged aerodynamic forces when studying ionospheric aerodynamics, while also providing new physical insights into physical mechanisms momentum exchange processes between a flowing plasma and immersed object.

Fate of Cd in Agricultural Soils: A Stable Isotope Approach to Anthropogenic Impact, Soil Formation, and Soil-Plant Cycling.

The application of mineral phosphate (P) fertilizers leads to an unintended Cd input into agricultural systems, which might affect soil fertility and quality of crops. The Cd fluxes at three arable sites in Switzerland were determined by a detailed analysis of all inputs (atmospheric deposition, mineral P fertilizers, manure, and weathering) and outputs (seepage water, wheat and barley harvest) during one hydrological year. The most important inputs were mineral P fertilizers (0.49 to 0.57 g Cd ha-1 yr-1) and manure (0.20 to 0.91 g Cd ha-1 yr-1). Mass balances revealed net Cd losses for cultivation of wheat (-0.01 to -0.49 g Cd ha-1 yr-1) but net accumulations for that of barley (+0.18 to +0.71 g Cd ha-1 yr-1). To trace Cd sources and redistribution processes in the soils, we used natural variations in the Cd stable isotope compositions. Cadmium in seepage water (δ114/110Cd = 0.39 to 0.79‰) and plant harvest (0.27 to 0.94‰) was isotopically heavier than in soil (-0.21 to 0.14‰). Consequently, parent material weathering shifted bulk soil isotope compositions to lighter signals following a Rayleigh fractionation process (ε ≈ 0.16). Furthermore, soil-plant cycling extracted isotopically heavy Cd from the subsoil and moved it to the topsoil. These long-term processes and not anthropogenic inputs determined the Cd distribution in our soils.

Mechanisms of Fe biofortification and mitigation of Cd accumulation in rice (Oryza sativa L.) grown hydroponically with Fe chelate fertilization

Cadmium contaminated rice from China has become a global food safety issue. Some research has suggested that chelate addition to substrates can affect metal speciation and plant metal content. We investigated the mitigation of Cd accumulation in hydroponically-grown rice supplied with EDTANa2Fe(II) or EDDHAFe(III).A japonica rice variety (Nipponbare) was grown in modified Kimura B solution containing three concentrations (0, 10, 100 μΜ) of the iron chelates EDTANa2Fe(II) or EDDHAFe(III) and 1 μΜ Cd. Metal speciation in solution was simulated by Geochem-EZ; growth and photosynthetic efficiency of rice were evaluated, and accumulation of Cd and Fe in plant parts was determined. Net Cd fluxes in the meristematic zone, growth zone, and maturation zone of roots were monitored by a non-invasive micro-test technology. Expression of Fe- and Cd-related genes in Fe-sufficient or Fe-deficient roots and leaves were studied by QRT-PCR.Compared to Fe deficiency, a sufficient or excess supply of Fe chelates significantly enhanced rice growth by elevating photosynthetic efficiency. Both Fe chelates increased the Fe content and decreased the Cd content of rice organs, except for the Cd content of roots treated with excess EDDHAFe(III). Compared to EDDHAFe(III), EDTANa2Fe(II) exhibited better mitigation of Cd accumulation in rice by generating the EDTANa2Cd complex in solution, decreasing net Cd influx and increasing net Cd efflux in root micro-zones. Application of EDTANa2Fe(II) and EDDHAFe(III) also reduced Cd accumulation in rice by inhibiting expression of genes involved in transport of Fe and Cd in the xylem and phloem.The ‘win-win’ situation of Fe biofortification and Cd mitigation in rice was achieved by application of Fe chelates. Root-to-stem xylem transport of Cd and redistribution of Cd in leaves by phloem transport can be regulated in rice through the use of Fe chelates that influence Fe availability and Fe-related gene expression. Fe fertilization decreased Cd influx and increased Cd efflux in rice roots.

Physiological responses of Allium cepa var. agrogarum L. plants to Cadmium stress

This study aimed to determine the effects of different Cd concentrations (0, 1, 10, 100, and 300 μM CdCl₂) on Allium plantlets. To achieve this goal, we examined the (1) dynamics of Cd²⁺ flux in the rhizosphere, (2) partitioning of Cd between roots and leaves, (3) formation of reactive oxygen species (ROS), (4) levels of H₂O₂ and chlorophyll, and (5) translocation of several macro- and micronutrients. A strong net Cd²⁺ influx was observed in the root apex after exposure to 100 μM Cd for 24 h. Exposure to either 1 or 10 μM Cd for 96 h presented no evident influence on root growth. However, treatments with 100 to 300 μM Cd for 72 h significantly inhibited root growth. ROS levels increased in roots and leaves with increasing Cd concentrations. The concentration of photosynthetic pigments, except for carotenoids on day 4, increased with increasing Cd concentrations and treatment duration. Cd accumulation decreased photosynthetic carbon assimilation but exerted no effects on diurnal patterns. Cd accumulated in roots and leaves, but a larger content was detected on roots than on leaves. Several macro- and micronutrients showed tissue- and concentration-specific responses to Cd.

Cadmium accumulation and toxicity in the unicellular alga Pseudokirchneriella subcapitata: Influence of metal-binding exudates and exposure time.

Predicting metal availability and toxicity for chronic (several hours or days) metal exposure scenarios, even for unicellular algae, is a major challenge to existing toxicity models. This is because several factors affecting metal uptake and toxicity, such as the release of metal-binding exudates, changes in the kinetics of metal uptake and toxicity over time, and algal physiological acclimation to internalized metals, are still poorly understood. The present study assessed the influence of these factors on Cd uptake and toxicity in laboratory batch cultures of the freshwater alga Pseudokirchneriella subcapitata. To do so, changes in the free Cd(2+) concentrations caused by the release of metal-binding algal exudates were monitored, (109)Cd accumulation in algal cells was measured, and Cd-induced inhibition of algal growth as a function of exposure time (from 12 h to 96 h) was followed. Results indicate that metal-binding exudates may decrease the proportion of the free Cd(2+) ion in solution up to 2-fold, a decrease that affects Cd uptake and toxicity. Pseudokirchneriella subcapitata has the capacity to decrease net Cd uptake rate on short time scales (<24 h), but this reduction in the Cd uptake rate disappeared after 24 h, and Cd toxicity occurred at relatively high Cd concentrations in solution. These data illustrate some of the pitfalls of standard algal toxicity assays, which were designed for acute exposures, and suggest how robust chronic bioassays might be developed.

A hemicellulose-bound form of silicon inhibits cadmium ion uptake in rice (Oryza sativa) cells.

Silicon (Si) alleviates cadmium (Cd) toxicity in rice (Oryza sativa). However, the chemical mechanisms at the single-cell level are poorly understood. Here, a suspension of rice cells exposed to Cd and/or Si treatments was investigated using a combination of plant cell nutritional, molecular biological, and physical techniques including in situ noninvasive microtest technology (NMT), polymerase chain reaction (PCR), inductively coupled plasma mass spectroscopy (ICP-MS), and atomic force microscopy (AFM) in Kelvin probe mode (KPFM). We found that Si-accumulating cells had a significantly reduced net Cd(2+) influx, compared with that in Si-limited cells. PCR analyses of the expression levels of Cd and Si transporters in rice cells showed that, when the Si concentration in the medium was increased, expression of the Si transporter gene Low silicon rice 1 (Lsi1) was up-regulated, whereas expression of the gene encoding the transporter involved in the transport of Cd, Natural resistance-associated macrophage protein 5 (Nramp5), was down-regulated. ICP-MS results revealed that 64% of the total Si in the cell walls was bound to hemicellulose constituents following the fractionation of the cell walls, and consequently inhibited Cd uptake. Furthermore, AFM in KPFM demonstrated that the heterogeneity of the wall surface potential was higher in cells cultured in the presence of Si than in those cultured in its absence, and was homogenized after the addition of Cd. These results suggest that a hemicellulose-bound form of Si with net negative charges is responsible for inhibition of Cd uptake in rice cells by a mechanism of [Si-hemicellulose matrix]Cd complexation and subsequent co-deposition.

Overexpression of bacterial γ-glutamylcysteine synthetase mediates changes in cadmium influx, allocation and detoxification in poplar.

Overexpression of bacterial γ-glutamylcysteine synthetase in the cytosol of Populus tremula × P. alba produces higher glutathione (GSH) concentrations in leaves, thereby indicating the potential for cadmium (Cd) phytoremediation. However, the net Cd(2+) influx in association with H(+) /Ca(2+) , Cd tolerance, and the underlying molecular and physiological mechanisms are uncharacterized in these poplars. We assessed net Cd(2+) influx, Cd tolerance and the transcriptional regulation of several genes involved in Cd(2+) transport and detoxification in wild-type and transgenic poplars. Poplars exhibited highest net Cd(2+) influxes into roots at pH 5.5 and 0.1 mM Ca(2+) . Transgenics had higher Cd(2+) uptake rates and elevated transcript levels of several genes involved in Cd(2+) transport and detoxification compared with wild-type poplars. Transgenics exhibited greater Cd accumulation in the aerial parts than wild-type plants in response to Cd(2+) exposure. Moreover, transgenic poplars had lower concentrations of O2 ˙(-) and H2 O2 ; higher concentrations of total thiols, GSH and oxidized GSH in roots and/or leaves; and stimulated foliar GSH reductase activity compared with wild-type plants. These results indicate that transgenics are more tolerant of 100 μM Cd(2+) than wild-type plants, probably due to the GSH-mediated induction of the transcription of genes involved in Cd(2+) transport and detoxification.

Inhibition of cadmium ion uptake in rice (Oryza sativa) cells by a wall‐bound form of silicon

The stresses acting on plants that are alleviated by silicon (Si) range from biotic to abiotic stresses, such as heavy metal toxicity. However, the mechanism of stress alleviation by Si at the single-cell level is poorly understood. We cultivated suspended rice (Oryza sativa) cells and protoplasts and investigated them using a combination of plant nutritional and physical techniques including inductively coupled plasma mass spectrometry (ICP-MS), the scanning ion-selective electrode technique (SIET) and X-ray photoelectron spectroscopy (XPS). We found that most Si accumulated in the cell walls in a wall-bound organosilicon compound. Total cadmium (Cd) concentrations in protoplasts from Si-accumulating (+Si) cells were significantly reduced at moderate concentrations of Cd in the culture medium compared with those from Si-limiting (-Si) cells. In situ measurement of cellular fluxes of the cadmium ion (Cd(2+) ) in suspension cells and root cells of rice exposed to Cd(2+) and/or Si treatments showed that +Si cells significantly inhibited the net Cd(2+) influx, compared with that in -Si cells. Furthermore, a net negative charge (charge density) within the +Si cell walls could be neutralized by an increase in the Cd(2+) concentration in the measuring solution. A mechanism of co-deposition of Si and Cd in the cell walls via a [Si-wall matrix]Cd co-complexation may explain the inhibition of Cd ion uptake, and may offer a plausible explanation for the in vivo detoxification of Cd in rice.

Ectomycorrhizas with Paxillus involutus enhance cadmium uptake and tolerance in Populus × canescens

Ectomycorrhizas (EMs), which are symbiotic organs formed between tree roots and certain fungi, can mediate cadmium (Cd) tolerance of host plants, but the underlying physiological and molecular mechanisms are not fully understood. To investigate EMs mediated Cd tolerance in woody plants, Populus × canescens was inoculated with Paxillus involutus (strain MAJ) to establish mycorrhizal roots. Mycorrhizal poplars and non-mycorrhizal controls were exposed to 0 or 50 μM CdSO4 . EMs displayed higher net Cd(2+) influx than non-mycorrhizal roots. Net Cd(2+) influx was coupled with net H(+) efflux and inactivation of plasma membrane (PM) H(+) -ATPases reduced Cd(2+) uptake of EMs less than of non-mycorrhizal roots. Consistent with higher Cd(2+) uptake in EMs, in most cases, transcript levels of genes involved in Cd(2+) uptake, transport and detoxification processes were increased in EMs compared to non-mycorrhizal roots. Higher CO2 assimilation, improved nutrient and carbohydrate status, and alleviated oxidative stress were found in mycorrhizal compared to non-mycorrhizal poplars despite higher Cd(2+) accumulation. These results indicate that mycorrhizas increase Cd(2+) uptake, probably by an enlarged root volume and overexpression of genes involved in Cd(2+) uptake and transport, and concurrently enhance Po. × canescens Cd tolerance by increased detoxification, improved nutrient and carbohydrate status and defence preparedness.

Cadmium uptake kinetics and plants factors of shoot Cd concentration

Accumulation of Cd in the shoots of plants grown on Cd contaminated soils shows considerable variation. A previous preliminary experiment established that one major reason for this variation was the rate of Cd influx into the roots (mol Cd cm−2 root s−1). However, this experiment did not distinguish between solubilization of soil Cd on the one hand and difference in Cd uptake kinetics on the other. The main objectives of the present study were thus to characterize Cd uptake kinetics of plants continuously exposed to Cd concentrations similar to those encountered in soils. Furthermore we determined the factors responsible for differences in shoot Cd concentration such as net Cd influx, root area-shoot dry weight ratio, shoot growth rate and proportion of Cd translocated to the shoot. Maize, sunflower, flax and spinach were grown in nutrient solution with five constant Cd concentrations varying from 0 to 1.0 μmol L−1. Root and shoot parameters as well as Cd uptake were determined at two harvest dates and from these data Cd net influx and shoot growth rates were calculated. Cadmium uptake kinetics, i.e. the net Cd influx vs. Cd solution concentration followed a straight line. Its slope is the root absorbing power, α, $$ \left( {\alpha ={{{\mathrm{Cd}\;\mathrm{net}\;\mathrm{influx}}} \left/ {{\mathrm{Cd}\;\mathrm{solution}\;\mathrm{concentration}}} \right.}} \right) $$ . The α values of spinach and flax were about double that of maize and sunflower (5 × 10−6 cm s−1 vs. 2.5 × 10−6 cm s−1). Spinach and flax had a 3–5 times higher shoot Cd concentration than maize and sunflower. The difference in shoot Cd concentration was partly due to the higher Cd influx but also to a higher translocation of Cd from root to shoot and also to a slower shoot growth rate.

The Exciton Origin of the Visible Circular Dichroism Spectrum of Bacteriorhodopsin

The visible CD spectrum of bacteriorhodpsin (bR) in purple membrane has a negative CD band at ~600 nm and a positive band at ~530 nm and has been variously interpreted as resulting from exciton coupling within the bR trimer, heterogeneity in protein conformation, or the presence of two distinct low-energy electronic transitions in bR. We have performed time-dependent density functional theory (TDDFT) calculations on the protonated Schiff base of retinal (retPSB) in bR to predict the intrinsic CD. The resulting spectroscopic parameters have been used to predict the long-wavelength CD spectrum of retPSB trimers. TDDFT, exciton theory, and classical polarizability (DeVoe) predict a strong negative couplet centered near 570 nm, with a magnitude in good agreement with experiment. Coupling of the retPSB chromophore with aromatic and peptide chromophores has been considered by means of perturbation theory and is responsible for the net positive CD of the 570 nm band. The visible CD spectrum of bR is dominated by exciton interactions.

Nitric oxide modulates cadmium influx during cadmium-induced programmed cell death in tobacco BY-2 cells

Nitric oxide (NO) is a bioactive gas and functions as a signaling molecule in plants exposed to diverse biotic and abiotic stresses including cadmium (Cd(2+)). Cd(2+) is a non-essential and toxic heavy metal, which has been reported to induce programmed cell death (PCD) in plants. Here, we investigated the role of NO in Cd(2+)-induced PCD in tobacco BY-2 cells (Nicotiana tabacum L. cv. Bright Yellow 2). In this work, BY-2 cells exposed to 150 microM CdCl(2) underwent PCD with TUNEL-positive nuclei, significant chromatin condensation and the increasing expression of a PCD-related gene Hsr203J. Accompanied with the occurring of PCD, the production of NO increased significantly. The supplement of NO by sodium nitroprusside (SNP) had accelerated the PCD, whereas the NO synthase inhibitor Nomega-nitro-L-arginine methyl ester hydrochloride (L-NAME) and NO-specific scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO) alleviated this toxicity. To investigate the mechanism by which NO exerted its function, Cd(2+) concentration was measured subsequently. SNP led more Cd(2+) content than Cd(2+) treatment alone. By contrast, the prevention of NO by L-NAME decreased Cd(2+) accumulation. Using the scanning ion-selective electrode technique, we analyzed the pattern and rate of Cd(2+) fluxes. This analysis revealed the promotion of Cd(2+) influxes into cells by application of SNP, while L-NAME and cPTIO reduced the rate of Cd(2+) uptake or even resulted in net Cd(2+) efflux. Based on these founding, we concluded that NO played a positive role in CdCl(2)-induced PCD by modulating Cd(2+) uptake and thus promoting Cd(2+) accumulation in BY-2 cells.