Influx In Roots Research Articles

Identification of cadmium-tolerant plant growth-promoting rhizobacteria and characterization of its Cd-biosorption and strengthening effect on phytoremediation: Development of a new amphibious-biocleaner for Cd-contaminated site

The use of plant growth-promoting rhizobacteria (PGPR) in decontaminating cadmium-contaminated soil and water is a sustainable and eco-friendly approach. This study aimed to isolate a PGPR strain from the rhizosphere soil of Solanum nigrum and evaluate its potential and mechanisms in remediating Cd-contaminated environments. The results showed that the isolated strain, Klebsiella sp. AW2, can tolerate 240 mg/L Cd2+. Batch biosorption experiments indicated that the optimal conditions for PGPR biosorption were a pH of 5.0, a biosorbent dosage of 1.0 g/L, and a Cd2+ concentration of 10 mg/L, resulting in a biosorption rate of 40.99%. Model fitting results revealed that the Cd biosorption process followed a uniform surface monolayer chemisorption mechanism, likely involving complexation with functional groups such as -NH, -OH, and -C=O, according to Fourier transform infrared spectrometer and desorption experiments. Furthermore, pot experiments demonstrated that PGPR application significantly enhanced the phytoremediation efficiency of Cd-contaminated soil, increasing the phytoextraction ratio by 32.41%. This improvement was primarily achieved by promoting S. nigrum growth and facilitating Cd horizontal transfer from rhizosphere soil to plants through influencing the rhizosphere soil physicochemical properties and Cd2+ influx in roots. In addition, the copy number of the 16S rRNA gene of the PGPR revealed that the PGPR was predominantly localized in the rhizosphere soil, directly leading to increased availability of Cd for plant uptake. Overall, these findings indicate that Klebsiella sp. AW2 is a promising biocleaner for Cd-contaminated environments and provide valuable insights into the application of biosorbents in phytoremediation efforts.

OsAMT1.1 knockout-induced decrease in cadmium absorption and accumulation by rice related to cadmium absorption-related gene downregulation

Cadmium (Cd) is a hazardous heavy metal that poses a serious risk to human health through the food chain, with rice being a significant vector because of its tendency to accumulate Cd. Nitrogen (N), an essential element for plant growth, also affects the Cd absorption and accumulation in crops. This study investigated the effects of N application on Cd absorption and accumulation in Cd-contaminated soils. Potting experiment showed that increasing N concentrations significantly increased the plant biomass and Cd contents in rice tissues. Ammonium (NH4+) transporter gene OsAMT1.1 knockout led to a substantial reduction in Cd absorption and accumulation in all rice tissues compared to that in the wild-type plants. Specifically, osamt1.1 mutants increased the Cd content in culm tissues, whereas it was reduced in brown rice. In addition, OsAMT1.1 knockout reduced Cd2+ influx in roots under NH4+-N addition, although OsAMT1.1 lacked Cd transport ability when expressed in yeast. Gene expression analysis revealed that OsAMT1.1 knockout reduced Cd absorption-related genes (OsIRT1, OsNRAMP1, and OsNRAMP5) expression levels. These finding highlight the critical role of N supply and OsAMT1.1 in regulating the Cd content in rice, offering insights into the molecular mechanisms of Cd transportation in plants.

Insights into the antagonistic effects of calcium on cadmium accumulation in peanuts (Arachis hypogaea L.)

Peanut (Arachis hypogaea L.) plant has a high requirement for calcium (Ca) during its growth and development, and possesses the ability to accumulate cadmium (Cd) from soil. However, the precise mechanisms underlying the antagonistic effects between Ca and Cd remain unclear. This study aimed to explore the dynamic changes in Cd accumulation in peanut seedlings by varying the Ca-to-Cd concentration ratio (CRCa/Cd) from 250 to 3500. Additionally, the influence of ion channel competition and cell wall fixation in the root on Cd accumulation in peanuts was explored by analyzing Cd chemical forms, subcellular distribution, pectin content, and Cd2+ fluxes using a non-invasive micro-test technique (NMT). The findings revealed that Cd accumulation in peanut seedlings was significantly lower when the CRCa/Cd was higher than 2000. In the Ca-pretreated seedlings (cell wall fixation treatment), Cd content in the shoots and roots decreased by 18.9% and 25.0%, respectively, compared with the simultaneous exposure to Ca and Cd (ion channel competition treatment). Cd2+ influx in peanut roots decreased by 55.8% in the Ca-pretreated group. However, increasing the competitive strength of Ca2+ and Cd2+ did not affect Cd2+ influx under normal Ca conditions (>2 mM Ca). Meanwhile, Ca pretreatment significantly increased Cd distribution in the root cell wall, pectate, and protein-binding forms, while significantly reducing Cd distribution in root soluble components and inorganic Cd forms. The pectin content in the roots increased by 128% and 226% in the Ca and Cd simultaneous exposure treatment and Ca pretreatment, respectively. These results suggest that Ca pretreatment enhanced Cd retention in the root cell wall. Overall, exogenous Ca effectively mitigated Cd accumulation in peanut plants when the CRCa/Cd was below 2000, and Ca2+ channels partially facilitate the entry of Cd2+ into peanut roots. Under normal Ca supply conditions, exogenous Ca reduced Cd accumulation in peanuts primarily through root cell wall fixation rather than ion channel competition. Our findings provide insights into the mechanism by which Ca alleviates the uptake and transfer of Cd in peanuts.

Synergistic Effects of Exogenous Nutrient Ions on the Real-Time Cadmium Extraction by an Accumulator

Bidens tripartita L. is a cadmium (Cd) accumulator. However, the real-time influx or efflux of Cd2+ around its root apex has not yet been performed. The object of this experiment was to compare the roles of added ions in solution on dynamic Cd extraction by B. tripartita root tip. Quartz sand was used to grow the seedling of B. tripartite. The Cd concentrations of all samples were determined by using ICP-OES after digestion. The Cd2+ influx around the root apex was measured in vivo, i.e., using non-invasive micro-test technology (NMT). The results showed that the Cd2+ influx was found to be decreased by 35.9%, 43.7%, 20.6%, and 57.5% under 10 μM Cd combined with high content Ca2+, Mg2+, Fe3+, or K+ (16 mM, 8 mM, 0.5 mM, 18 mM, respectively), compared to that under 10 μM Cd stress. But Cd treatments with low content ions with 0.05 mM Fe3+ or 0.5 mM S increased the Cd2+ influx in roots by 20.5% and 34.6%, respectively. It was also found that Cd treatment with high concentrations of Ca2+ or K+ increased the shoot biomass of B. tripartita seedlings. Chl a and b contents were significantly decreased in the Cd treatments with low concentrations of Fe3+ or S compared to those under Cd stress alone, and the dehydrogenase activity of the roots decreased in the treatment of Cd with 0.05 mM Fe3+ or 0.5 mM S. Our results indicate that the addition of 0.05 mM Fe3+ or 0.5 mM S promoted Cd2+ influx and Cd uptake by B. tripartita. Unlike traditional measurement, the Cd2+ movements of three-dimensional space around the B. tripartita root tip had been performed by NMT. It was suggested that the effects of S and Fe3+ on the remediation potential of B. tripartita need to be further researched in the future. The results of this study provided a real-time and micro-dynamic theoretical basis for phytoremediation mechanisms.

Carbon Nanoparticles Promoted the Absorption of Potassium Ions by Tobacco Roots via Regulation of K+ Flux and Ion Channel Gene Expression

Background: The regulatory effects of carbon nanomaterials (CNMs) on plant growth and their potential applications in agriculture have attracted a great deal of attention from researchers. CNMs have been shown to promote nutrient absorption and increase plant growth. However, the mechanisms by which CNMs affect plant growth and nutrient absorption are still unknown. Methods: The tobacco seedling biomass, potassium (K+) concentration, and accumulation in hydroponic were investigated to exposure of carbon nanoparticles (CNPs). To directly observe the effect of CNPs on K+ uptake by roots, we employed a noninvasive micro-test technique (NMT) to detect the net flux of K+ on the surface of tobacco roots. The K+-depletion experiment was carried out to explore the kinetic characteristics of K+ absorption, and qRT-PCR was used to monitor the expression levels of the K+ channel gene. Results: The results showed that tobacco seedling biomass significantly improved at 10 mg·L-1 CNP treatments, and K+ concentration and accumulation both in roots and shoots increased with 10 and 20 mg·L-1 CNPs. CNP treatments changed the flow rate of K+ from efflux to influx in tobacco roots; this was observed both in plants cultivated in a CNP-containing medium and after the addition of CNPs to previously untreated plants. A depletion test also showed that CNPs improved the K+ absorption capacity and low-K+ tolerance of tobacco seedlings. Conclusion: CNPs enhanced the K+ absorption capacity and low-K+ tolerance of tobacco seedlings. The promotion of K+ absorption by CNPs was closely related to the activation of K+ influx channel genes and inhibition of the K+ outflow channel gene. The K+ flux response and ion channel gene expression to CNPs in plants reveal the mechanism whereby CNPs promote plant nutrient absorption.

Inventory of cadmium-transporter genes in the root of mangrove plant Avicennia marina under cadmium stress

Mangrove Avicennia marina has the importantly potential for cadmium (Cd) pollution remediation in coastal wetlands. Unfortunately, the molecular mechanisms and transporter members for Cd uptake by the roots of A. marina are not well documented. In this study, photosynthetic and phenotypic analysis indicated that A. marina is particularly tolerant to Cd. The content and flux analysis indicated that Cd is mainly retained in the roots, with greater Cd influx in fine roots than that in coarse roots, and higher Cd influx in the root meristem zone as well. Using transcriptomic analysis, a total of 5238 differentially expressed genes were identified between the Cd treatment and control group. Moreover, we found that 54 genes were responsible for inorganic ion transport. Among these genes, AmHMA2, AmIRT1, and AmPCR2 were localized in the plasma membrane and AmZIP1 was localized in both plasma membrane and cytoplasm. All above gene encoding transporters showed significant Cd transport activities using function assay in yeast cells. In addition, the overexpression of AmZIP1 or AmPCR2 in Arabidopsis improved the Cd tolerance of transgenic plants. This is particularly significant as it provides insight into the molecular mechanism for Cd uptake by the roots of mangrove plants and a theoretical basis for coastal wetland phytoremediation.

Salt-Stress-Induced Ion Transport Contributes to K+/Na+ Homeostasis in Roots of Ping’ou Hybrid Hazelnut

Soil salinity is a worldwide problem that adversely affects plant growth and development. Soil salinization in Xinjiang of China is very serious. Ping’ou hybrid hazelnut, as an important ecological and economic tree species, as well as a salt-tolerant plant, has been grown in Xinjiang for over 20 years. Understanding the salt-tolerance mechanism of Ping’ou hybrid hazelnut is of great significance for the breeding of salt-tolerant varieties and the rational utilization of salinized land. In this study, ‘Liaozhen 7’, a fine variety of Ping’ou hybrid hazelnut, was selected as test material, and seedlings were treated with 0 (control), 50, 100 and 200 mM NaCl. Subsequently, the pattern of NaCl-induced fluxes of Na+, K+ and H+ in the root meristematic zone and their response to ion transport inhibitors were studied using non-invasive micro-test technology (NMT). Different concentrations of NaCl stress significantly increased the Na+ concentration in roots, while K+ concentration decreased first and then increased with the increase of NaCl concentration. Meanwhile, NaCl stress induced a significant decline in K+/Na+ ratio. Control and 200 mM NaCl-induced Na+ and K+ fluxes in roots exhibited an outward efflux, whereas an inward flux was observed for H+. Under 200 mM NaCl stress, the average rates of net Na+ and K+ efflux, as well as H+ influx in roots were significantly increased, which were 11.6, 6.7 and 2.3 times higher than that of control, respectively. Furthermore, pharmacological experiments showed that 200 mM NaCl-induced Na+ efflux; H+ influx was significantly suppressed by amiloride, an inhibitor of plasma membrane (PM) Na+/H+ antiporter, and sodium vanadate, an inhibitor of PM H+-ATPase. Net Na+ efflux and H+ influx induced by NaCl decreased by 89.9% and 135.0%, respectively. The NaCl-induced Na+ efflux was mediated by a Na+/H+ antiporter using energy provided by PM H+-ATPase. The NaCl-induced K+ efflux was significantly restricted by tetraethylamine chloride, a K+ channel inhibitor, and promoted by sodium vanadate, which decreased by 111.2% and increased by 80.8%, respectively, indicating that K+ efflux was regulated by depolarization-activated outward-rectifying K+ channels and non-selective cation channels (NSCCs). In conclusion, NMT data revealed that NaCl stress up regulated the root Na+/H+ antiporter and H+ pump (an activity of PM Na+/H+ antiport system) of ‘Liaozhen 7’, which compelled the Na+/H+ exchange across the PM and restricted K+ loss via depolarization-activated K+ channels and NSCCs simultaneously, thereby maintaining the K+/Na+ homeostasis and higher salt tolerance.

OsAMT1.1 Expression by Nitrate-Inducible Promoter of OsNAR2.1 Increases Nitrogen Use Efficiency and Rice Yield

Nitrate (NO3–) and ammonium (NH4+) are two main inorganic nitrogen (N) sources during crop growth. Here, we enhanced the expression of OsAMT1.1, which encodes a NH4+ transporter, using the NO3–-inducible promoter of OsNAR2.1 and an ubiquitin promoter in transgenic rice plants. Under field condition of 120 kg /hm2 N, agronomic N use efficiency, N recovery efficiency and N transport efficiency, and grain yield of the pOsNAR2.1:OsAMT1.1 transgenic lines were increased compared with those of the wild type (WT) and the pUbi:OsAMT1.1 transgenic plants. Under 2.0 mmol/L NO3– + 0.5 mmol/L NH4+ and 0.5 mmol/L NO3– + 2.0 mmol/L NH4+ conditions of hydroponic culture, compared with the WT, both biomass and total N content were increased in the pOsNAR2.1:OsAMT1.1 transgenic lines. However, biomass was significantly reduced in pUbi:OsAMT1.1 transgenic plants under 0.5 mmol/L NO3– + 2.0 mmol/L NH4+ condition. The lines expressing pOsNAR2.1:OsAMT1.1 exhibited increased OsAMT1.1 expression and 15NH4+ influx in roots under both 2.0 mmol/L NO3– + 0.5 mmol/L NH4+ and 0.5 mmol/L NO3– + 2.0 mmol/L NH4+ conditions. Our study showed that expression of OsAMT1.1 can be promoted when driven by the OsNAR2.1 promoter, especially under high-level nitrate condition, leading to enhancement of NH4+ uptake, N use efficiency and grain yield.

Pathways and Characteristics of Lead Uptake and Transportation in Rhus chinensis Mill

Rhus chinensis Mill is a potential plant for phytoremediation of Pb and is able to uptake a copious amount of Pb. However, little is known about the pathways and properties of Pb uptake in this plant. Here, controlled experiments were used to assess Pb uptake and translocation in R. chinensis. The whole time-kinetics of Pb uptake were divided into two stages: rapid uptake and slower accumulation, and the two processes were fitted with a linear model. The concentration-dependent kinetics of Pb uptake were characterized by a modified Michaelis–Menten equation. The Km and Vmax value of Pb influx in roots were 19.44 and 14.83, respectively. Transpiration inhibitors had no significant effect on the Pb concentration of root and shoot. Low temperatures (4 °C) and metabolic inhibitors (carbonyl cyanide m-chlorophenylhydrazone and 2,4-dinitrophenol) significantly reduced the Pb concentration in the roots and leaves of R. chinensis plants. Furthermore, the addition of calcium ion channel inhibitors and protein synthesis inhibitors significantly reduced the Pb concentration in the roots of R. chinensis plants. These results show that both active and passive processes of Pb uptake and translocation exist in the roots of R. chinensis plants. In addition, Pb uptake by the roots of R. chinensis plants was related to calcium ion channels.

Ectomycorrhizal Fungal Strains Facilitate Cd2+ Enrichment in a Woody Hyperaccumulator under Co-Existing Stress of Cadmium and Salt.

Cadmium (Cd2+) pollution occurring in salt-affected soils has become an increasing environmental concern in the world. Fast-growing poplars have been widely utilized for phytoremediation of soil contaminating heavy metals (HMs). However, the woody Cd2+-hyperaccumulator, Populus × canescens, is relatively salt-sensitive and therefore cannot be directly used to remediate HMs from salt-affected soils. The aim of the present study was to testify whether colonization of P. × canescens with ectomycorrhizal (EM) fungi, a strategy known to enhance salt tolerance, provides an opportunity for affordable remediation of Cd2+-polluted saline soils. Ectomycorrhization with Paxillus involutus strains facilitated Cd2+ enrichment in P. × canescens upon CdCl2 exposures (50 μM, 30 min to 24 h). The fungus-stimulated Cd2+ in roots was significantly restricted by inhibitors of plasmalemma H+-ATPases and Ca2+-permeable channels (CaPCs), but stimulated by an activator of plasmalemma H+-ATPases. NaCl (100 mM) lowered the transient and steady-state Cd2+ influx in roots and fungal mycelia. Noteworthy, P. involutus colonization partly reverted the salt suppression of Cd2+ uptake in poplar roots. EM fungus colonization upregulated transcription of plasmalemma H+-ATPases (PcHA4, 8, 11) and annexins (PcANN1, 2, 4), which might mediate Cd2+ conductance through CaPCs. EM roots retained relatively highly expressed PcHAs and PcANNs, thus facilitating Cd2+ enrichment under co-occurring stress of cadmium and salinity. We conclude that ectomycorrhization of woody hyperaccumulator species such as poplar could improve phytoremediation of Cd2+ in salt-affected areas.

Methane control of cadmium tolerance in alfalfa roots requires hydrogen sulfide

Hydrogen sulfide (H2S) is well known as a gaseous signal in response to heavy metal stress, while methane (CH4), the most prevalent greenhouse gas, confers cadmium (Cd) tolerance. In this report, the causal link between CH4 and H2S controlling Cd tolerance in alfalfa (Medicago sativa) plants was assessed. Our results observed that the administration of CH4 not only intensifies H2S metabolism, but also attenuates Cd-triggered growth inhibition in alfalfa seedlings, which were parallel to the alleviated roles in the redox imbalance and cell death in root tissues. Above results were not observed in roots after the removal of endogenous H2S, either in the presence of either hypotaurine (HT; a H2S scavenger) or DL-propargylglycine (PAG; a H2S biosynthesis inhibitor). Using in situ noninvasive microtest technology (NMT) and inductively coupled plasma mass spectroscopy (ICP-MS), subsequent results confirmed the participation of H2S in CH4-inhibited Cd influx and accumulation in roots, which could be explained by reestablishing glutathione (GSH) pool (reduced/oxidized GSH and homoglutathione) homeostasis and promoting antioxidant defence. Overall, our results clearly revealed that H2S operates downstream of CH4 enhancing tolerance against Cd stress, which are significant for both fundamental and applied plant biology.

Gamma-aminobutyric acid (GABA) alleviates salt damage in tomato by modulating Na+ uptake, the GAD gene, amino acid synthesis and reactive oxygen species metabolism

BackgroundSalt stress is a serious abiotic stress that caused crop growth inhibition and yield decline. Previous studies have reported on the the synthesis of gamma-aminobutyric acid (GABA) and its relationship with plant resistance under various abiotic stress. However, the relationship between exogenous GABA alleviating plant salt stress damage and ion flux, amino acid synthesis, and key enzyme expression remains largely unclear. We investigated plant growth, Na+ transportation and accumulation, reactive oxygen species (ROS) metabolism and evaluated the effect of GABA on amino acids, especially SlGADs gene expression and the endogenous GABA content of tomato (Solanum lycopersicum L.) seedlings treated with or without 5 mmol·L− 1 GABA under 175 mmol·L− 1 NaCl stress.ResultsExogenous application of GABA significantly reduced the salt damage index and increased plant height, chlorophyll content and the dry and fresh weights of tomato plants exposed to NaCl stress. GABA significantly reduced Na+ accumulation in leaves and roots by preventing Na+ influx in roots and transportation to leaves. The transcriptional expression of SlGAD1–3 genes were induced by NaCl stress especially with GABA application. Among them, SlGAD1 expression was the most sensitive and contributed the most to the increase in glutamate decarboxylase (GAD) activity induced by NaCl and GABA application; Exogenous GABA increased GAD activity and amino acid contents in tomato leaves compared with the levels under NaCl stress alone, especially the levels of endogenous GABA, proline, glutamate and eight other amino acids. These results indicated that SlGADs transcriptional expression played an important role in tomato plant resistance to NaCl stress with GABA application by enhancing GAD activity and amino acid contents. GABA significantly alleviated the active oxygen-related injury of leaves under NaCl stress by increasing the activities of antioxidant enzymes and decreasing the contents of active oxygen species and malondialdehyde.ConclusionExogenous GABA had a positive effect on the resistance of tomato seedlings to salt stress, which was closely associated with reducing Na+ flux from root to leaves, increasing amino acid content and strengthening antioxidant metabolism. Endogenous GABA content was induced by salt and exogenous GABA at both the transcriptional and metabolic levels.

Ethylene-mediated apoplastic barriers development involved in cadmium accumulation in root of hyperaccumulator Sedum alfredii

Ethylene is an important phytohormone for plant adaptation to heavy metal stress. However, the effects of ethylene on radial apoplastic transport of Cd remain elusive. This study investigated the role of ethylene on apoplastic barriers development and consequences for Cd uptake in Sedum alfredii. In response to Cd, endogenous ethylene production in hyperaccumulating ecotype (HE) roots was decreased due to the down-regulated expressions of ethylene biosynthesis genes, while the opposite result was observed in non-hyperaccumulating ecotype (NHE). Interestingly, the ethylene emission in HE was always higher than that in NHE, regardless of Cd concentrations. Results of exogenous application of ethylene biosynthesis precursor/inhibitor indicate that ethylene with high level would delay the formation of apoplastic barriers in HE through restraining phenylalanine ammonia lyase activity and gene expressions related to lignin/suberin biosynthesis. Simultaneously, correlation analyses suggest that Cd-induced apoplastic barriers formation may be also regulated by ethylene signaling. By using an apoplastic bypass tracer and scanning ion-selected electrode, we observed that the delayed deposition of apoplastic barriers significantly promoted Cd influx in roots. Taken together, high endogenous ethylene in HE postponed the formation of apoplastic barriers and thus promoted the Cd accumulation in the apoplast of roots.

Co-Overexpression of OsNAR2.1 and OsNRT2.3a Increased Agronomic Nitrogen Use Efficiency in Transgenic Rice Plants.

The NO3 - transporter plays an important role in rice nitrogen acquisition and nitrogen-use efficiency. Our previous studies have shown that the high affinity systems for nitrate uptake in rice is mediated by a two-component NRT2/NAR2 transport system. In this study, transgenic plants were successful developed by overexpression of OsNAR2.1 alone, OsNRT2.3a alone and co-overexpression of OsNAR2.1 and OsNRT2.3a. Our field experiments indicated that transgenic lines expressing p35S:OsNAR2.1 or p35S:OsNAR2.1-p35S:OsNRT2.3a constructs exhibited increased grain yields of approximately 14.1% and 24.6% compared with wild-type (cv. Wuyunjing 7, WT) plants, and the agricultural nitrogen use efficiency increased by 15.8% and 28.6%, respectively. Compared with WT, the 15N influx in roots of p35S:OsNAR2.1 and p35S: OsNAR2.1-p35S:OsNRT2.3a lines increased 18.9%‑27.8% in response to 0.2 mM, 2.5 mM 15NO3 –, and 1.25 mM 15NH4 15NO3, while there was no significant difference between p35S:OsNAR2.1 and p35S:OsNAR2.1-p35S:OsNRT2.3a lines; only the 15N distribution ratio of shoot to root for p35S:OsNAR2.1-p35S:OsNRT2.3a lines increased significantly. However, there were no significant differences in nitrogen use efficiency, 15N influx in roots and the yield between the p35S:NRT2.3a transgenic lines and WT. This study indicated that co-overexpression of OsNAR2.1 and OsNRT2.3a could increase rice yield and nitrogen use efficiency.

A comparative study of root cadmium radial transport in seedlings of two wheat (Triticum aestivum L.) genotypes differing in grain cadmium accumulation

The radial transport of cadmium (Cd) is essential for Cd influx in roots. The role of radial transport pathway on the Cd translocation from root to shoot among wheat genotypes are still poorly understood. This study explored the role of apoplastic and symplastic pathway on root Cd uptake and root-to-shoot translocation in Zhenmai 10 (ZM10, high Cd in grains) and Aikang 58 (AK58, low Cd in grains). Under Cd treatment, the deposition of Casparian strips (CSs) and suberin lamellae (SL) initiated closer to the root apex in ZM10 than that in AK58, which resulted in the lower Cd concentration in apoplastic fluid of ZM10. Simultaneously, Cd-induced expression levels of genes related to Cd uptake in roots were significantly higher in AK58 by contrast with ZM10, contributing to the symplastic Cd accumulation in AK58 root. Moreover, the addition of metabolic inhibitor CCCP noticeably decreased the Cd accumulation in root of both genotypes. Intriguingly, compared to ZM10, greater amounts of Cd were sequestrated in the cell walls and vacuoles in roots of AK58, limiting the translocation of Cd from root to shoot. Furthermore, the elevated TaHMA2 expression in ZM10 indicates that ZM10 had a higher capacity of xylem loading Cd than AK58. All of these results herein suggest that the radial transport is significant for Cd accumulation in roots, but it cannot explain the difference in root-to-shoot translocation of Cd in wheat genotypes with contrast Cd accumulation in grains.

The pathway of transmembrane cadmium influx via calcium-permeable channels and its spatial characteristics along rice root.

To develop elite crops with low cadmium (Cd), a fundamental understanding of the mechanism of Cd uptake by crop roots is necessary. Here, a new mechanism for Cd2+ entry into rice root cells was investigated. The results showed that Cd2+ influx in rice roots exhibited spatially and temporally dynamic patterns. There was a clear longitudinal variation in Cd uptake along rice roots, with the root tip showing much higher Cd2+ influx and concentration than the root mature zone, which might be due to the much higher expression of the well-known Cd transporter genes OsIRT1, OsNRAMP1, OsNRAMP5, and OsZIP1 in the root tip. Both the net Cd2+ influx and the uptake of Cd in rice roots were highly inhibited by ion channel blockers Gd3+ and TEA+, supplementation of Ca2+ and K+, and the plasma membrane H+-ATPase inhibitor vanadate, with Gd3+ and Ca2+ showing the most inhibitory effects. Furthermore, Ca2+- or Gd3+-induced reduction in Cd2+ influx and Cd uptake did not coincide with the expression of Cd transporter genes, but with that of two Ca channel genes, OsAAN4 and OsGLR3.4. These results indicate that Cd transporters are in part responsible for Cd2+ entry into rice root, and provide a new perspective that the Ca channels OsAAN4 and OsGLR3.4 might play an important role in rice root Cd uptake.

Silicon alleviates cadmium toxicity in wheat seedlings (Triticum aestivum L.) by reducing cadmium ion uptake and enhancing antioxidative capacity.

Cadmium (Cd) is a toxic element that poses a great threat to human health, while silicon (Si) is a beneficial element and has been shown to have a mitigation effect on plants under Cd toxicity. However, the mechanisms underlying the role of Si in alleviating Cd toxicity are still poorly understood in wheat. Therefore, growth status, photosynthesis parameters, root morphology, antioxidant system, and Cd2+ uptake and flux under Cd toxicity were studied through hydroponic experiment, aiming to explore the mitigation of Si on Cd toxicity in wheat seedlings. The results showed that Si supply improved plant biomass as well as photosynthetic but had little effects on root morphology of seedlings under Cd stress. Si addition decreased Cd contents both in shoots and roots. In situ measurements of Cd2+ flux showed that Si significantly inhibited the net Cd2+ influx in roots of wheat. Si also mitigated the oxidative stress in wheat leaves by decreasing malondialdialdehyde (MDA) and hydrogen peroxide (H2O2) contents as well as by increasing superoxide dismutase (SOD) and guaiacol peroxidase (POD) activity. Overall, the results revealed that Si could alleviate Cd toxicity in wheat seedlings by improving plant growth and antioxidant capacity and by decreasing Cd uptake and lipid peroxidation.

POsNAR2.1:OsNAR2.1 expression enhances nitrogen uptake efficiency and grain yield in transgenic rice plants.

SummaryThe nitrate (NO3−) transporter has been selected as an important gene maker in the process of environmental adoption in rice cultivars. In this work, we transferred another native OsNAR2.1 promoter with driving OsNAR2.1 gene into rice plants. The transgenic lines with exogenous pOsNAR2.1:OsNAR2.1 constructs showed enhanced OsNAR2.1 expression level, compared with wild type (WT), and 15N influx in roots increased 21%–32% in response to 0.2 mm and 2.5 mm 15NO3− and 1.25 mm 15 NH 4 15 NO 3. Under these three N conditions, the biomass of the pOsNAR2.1:OsNAR2.1 transgenic lines increased 143%, 129% and 51%, and total N content increased 161%, 242% and 69%, respectively, compared to WT. Furthermore in field experiments we found the grain yield, agricultural nitrogen use efficiency (ANUE), and dry matter transfer of pOsNAR2.1:OsNAR2.1 plants increased by about 21%, 22% and 21%, compared to WT. We also compared the phenotypes of pOsNAR2.1:OsNAR2.1 and pOsNAR2.1:OsNRT2.1 transgenic lines in the field, found that postanthesis N uptake differed significantly between them, and in comparison with the WT. Postanthesis N uptake (PANU) increased approximately 39% and 85%, in the pOsNAR2.1:OsNAR2.1 and pOsNAR2.1:OsNRT2.1 transgenic lines, respectively, possibly because OsNRT2.1 expression was less in the pOsNAR2.1:OsNAR2.1 lines than in the pOsNAR2.1:OsNRT2.1 lines during the late growth stage. These results show that rice NO 3 – uptake, yield and NUE were improved by increased OsNAR2.1 expression via its native promoter.

Paxillus involutus-Facilitated Cd2+ Influx through Plasma Membrane Ca2+-Permeable Channels Is Stimulated by H2O2 and H+-ATPase in Ectomycorrhizal Populus × canescens under Cadmium Stress.

Using a Non-invasive Micro-test Technique, flux profiles of Cd2+, Ca2+, and H+ were investigated in axenically grown cultures of two strains of Paxillus involutus (MAJ and NAU), ectomycorrhizae formed by these fungi with the woody Cd2+-hyperaccumulator, Populus × canescens, and non-mycorrhizal (NM) roots. The influx of Cd2+ increased in fungal mycelia, NM and ectomycorrhizal (EM) roots upon a 40-min shock, after short-term (ST, 24 h), or long-term (LT, 7 days) exposure to a hydroponic environment of 50 μM CdCl2. Cd2+ treatments (shock, ST, and LT) decreased Ca2+ influx in NM and EM roots but led to an enhanced influx of Ca2+ in axenically grown EM cultures of the two P. involutus isolates. The susceptibility of Cd2+ flux to typical Ca2+ channel blockers (LaCl3, GdCl3, verapamil, and TEA) in fungal mycelia and poplar roots indicated that the Cd2+ entry occurred mainly through Ca2+-permeable channels in the plasma membrane (PM). Cd2+ treatment resulted in H2O2 production. H2O2 exposure accelerated the entry of Cd2+ and Ca2+ in NM and EM roots. Cd2+ further stimulated H+ pumping activity benefiting NM and EM roots to maintain an acidic environment, which favored the entry of Cd2+ across the PM. A scavenger of reactive oxygen species, DMTU, and an inhibitor of PM H+-ATPase, orthovanadate, decreased Ca2+ and Cd2+ influx in NM and EM roots, suggesting that the entry of Cd2+ through Ca2+-permeable channels is stimulated by H2O2 and H+ pumps. Compared to NM roots, EM roots exhibited higher Cd2+-fluxes under shock, ST, and LT Cd2+ treatments. We conclude that ectomycorrhizal P. × canescens roots retained a pronounced H2O2 production and a high H+-pumping activity, which activated PM Ca2+ channels and thus facilitated a high influx of Cd2+ under Cd2+ stress.

The Plant as Metaorganism and Research on Next-Generation Systemic Pesticides - Prospects and Challenges.

Systemic pesticides (SPs) are usually recommended for soil treatments and as seed coating agents and are taken up from the soil by involving various plant-mediated processes, physiological, and morphological attributes of the root systems. Microscopic insights and next-generation sequencing combined with bioinformatics allow us now to identify new functions and interactions of plant-associated bacteria and perceive plants as meta-organisms. Host symbiotic, rhizo-epiphytic, endophytic microorganisms and their functions on plants have not been studied yet in accordance with uptake, tanslocation and action of pesticides. Root tips exudates mediated by rhizobacteria could modify the uptake of specific pesticides while bacterial ligands and enzymes can affect metabolism and fate of pesticide within plant. Over expression of specific proteins in cell membrane can also modify pesticide influx in roots. Moreover, proteins and other membrane compartments are usually involved in pesticide modes of action and resistance development. In this article it is discussed what is known of the physiological attributes including apoplastic, symplastic, and trans-membrane transport of SPs in accordance with the intercommunication dictated by plant–microbe, cell to cell and intracellular signaling. Prospects and challenges for uptake, translocation, storage, exudation, metabolism, and action of SPs are given through the prism of new insights of plant microbiome. Interactions of soil applied pesticides with physiological processes, plant root exudates and plant microbiome are summarized to scrutinize challenges for the next-generation pesticides.