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1.
Phytochelatins (PCs) are metal binding peptides involved in heavy metal detoxification. To assess whether enhanced phytochelatin
synthesis would increase heavy metal tolerance and accumulation in plants, we overexpressed the Arabidopsis phytochelatin
synthase gene ( AtPCS1) in the non-accumulator plant Nicotiana tabacum. Wild-type plants and plants harbouring the Agrobacterium rhizogenes rolB oncogene were transformed with a 35S
AtPCS1 construct. Root cultures from rolB plants could be easily established and we demonstrated here that they represent a reliable system to study heavy metal tolerance.
Cd 2+ tolerance in cultured rolB roots was increased as a result of overexpression of AtPCS1, and further enhanced when reduced glutathione (GSH, the substrate of PCS1) was added to the culture medium. Accordingly,
HPLC analysis showed that total PC production in PCS1-overexpressing rolB roots was higher than in rolB roots in the presence of GSH. Overexpression of AtPCS1 in whole seedlings led to a twofold increase in Cd 2+ accumulation in the roots and shoots of both rolB and wild-type seedlings. Similarly, a significant increase in Cd 2+ accumulation linked to a higher production of PCs in both roots and shoots was observed in adult plants. However, the percentage
of Cd 2+ translocated to the shoots of seedlings and adult overexpressing plants was unaffected. We conclude that the increase in
Cd 2+ tolerance and accumulation of PCS1 overexpressing plants is directly related to the availability of GSH, while overexpression of phytochelatin synthase does
not enhance long distance root-to-shoot Cd 2+ transport. 相似文献
2.
Heavy metal pollution has become one of the most serious environmental problems today. To develop a more efficient plant to clean up heavy metal contaminated soils, a γ‐glutamylcysteine synthetase (GCS) cDNA, named PaGCS, was isolated by PCR from Phragmites australis. The PaGCS sequence was transformed via agroinfection into the heavy metal intolerant grass Agrostis palustris. Five confirmed transgenic A. palustris plants expressing PaGCS were compared with the wild‐type line for growth and Cd 2+ accumulation, as well as for the expression of a number of phytochelatin synthesis and stress‐responsive enzymes when challenged with Cd 2+ stress. GCS and phytochelatin synthase (PCS) were up‐regulated in the transgenic lines. All the transgenic lines accumulated more Cd 2+ and phytochelatins (PCs) than the wild‐type line, and three of the five lines grew more effectively than the wild‐type after either five or 21 d of Cd 2+ stress. Variation among the transgenics was observed for the distribution of Cd 2+ in the root, shoot and leaf. The malondialdehyde content of all the transgenic lines was lower than that of the wild type under Cd 2+ treatment, while the activity of both superoxide dismutase and peroxidase present in the transgenic lines increased markedly 24 h after Cd 2+ stress, and then rapidly declined. 相似文献
3.
Possible roles of cell wall and cytoplasmic peptides in the tolerance of cells to Cu 2+ and Cd 2+ ions were studied in suspension-cultured cells of tomato ( Lycopersicon esculentum L. cv. Palace). Cu 2+ and Cd 2+ ions inhibited growth of wild type cells at concentrations more than 100 and 200 μM, respectively. Tomato cells readily developed
tolerance to Cd 2+ ions up to 1 mM but not to Cu 2+ ions, after repeated subculturings in the presence of the respective ions. Such a metal-specific adaptation of cells was
not due to the difference in the total uptakes between Cd 2+ and Cu 2+ ions by cells. Wild-type cells accumulated Cd 2+ preferentially into the cytoplasmic peptide fraction and Cu 2+ into the cell-wall fraction, when grown under the subtoxic metal conditions. Under excess metal conditions, Cd-tolerant cells
produced greater amounts of Cd-binding peptides in the cytoplasm and retained lesser amounts of Cd 2+ ions in the cell wall than did wild-type cells. In contrast, tomato cells grown in the presence of Cu 2+ ions synthesized no detectable amounts of Cu-binding peptides in the cytoplasm and retained most of the Cu 2+ in the cell-wall fraction, irrespective of cell lines.
These results suggested that the cytoplasmic peptides rather than cell wall properties have a primary role in the response
of tomato cells to excess metal environments. 相似文献
4.
- Many saline-alkali soils around the world are polluted by the heavy metal Cd, restricting the development of agriculture and ecology in those regions. The halophyte Salicornia europaea L. is capable of growing healthily in Cd-contaminated saline-alkali soil, suggesting that the species is tolerant to stress caused by both salt and heavy metals. In this study, the mechanism of Cd tolerance in this species was explored under 200 mM NaCl.
- Flame spectrophotometric assays for ions content and spectrophotometric for organic soluble substances, antioxidant enzyme activity, phytochelatins (PCs) content and phytochelatin synthase (PCS) activity, the photosynthetic parameters by portable photosynthesis measurement system, genes expression by qRT-PCR analysis were carried out.
- Cd treatment significantly decreased the dry weight, photosynthetic rate, K+, Zn2+, and Fe2+/3+ content, while significantly increasing Na+ and Cd+, soluble organic matter, and reactive oxygen species (ROS) levels. Compared with Cd treatment at 0 mM NaCl, Cd treatment at 200 mM NaCl significantly increased dry weight and photosynthetic rate while significantly decreasing ROS content through increased antioxidant enzyme activity. When exposed to Cd stress, treatment with 200 mM NaCl significantly increased PCs content and PCS activity and up-regulated the expression of the phytochelatin synthase genes CDA1 and PCS1 were, thereby increasing resistance to Cd.
- NaCl treatment increases the tolerance of S. europaea to the heavy metal Cd by growing rapidly, reducing the quantity of Cd2+ from entering the plant shoots, increasing the levels of PCs that chelate Cd2+, thereby reducing its toxicity.
相似文献
5.
Industry residues, phosphate fertilisers and wastewater as a source of irrigation have considerably increased levels of heavy metals in the soil, mainly cadmium (Cd 2+). To test the effects of a calcium (Ca 2+) treatment on Cd 2+ accumulation and plant tolerance to this heavy metal, plants of two citrus genotypes, Cleopatra mandarin (CM) and Carrizo citrange (CC), were watered with increasing concentrations of Cd 2+, and phytochelatin (PC) and glutathione (GSH) content were measured. Both genotypes were able to synthesise PCs in response to heavy metal intoxication, although CM seems to be a better Cd 2+ excluder than CC. However, data indicate that CC plants had a higher capacity for regenerating GSH than CM plants. In this context, the effects of Ca 2+ treatment on Cd 2+ accumulation, plant survival and PC, GSH and oxidised glutathione (GSSG) content were assessed. Data indicate that treatment with Ca 2+ had two positive effects on citrus physiology: it reduced Cd +2 uptake into roots and also increased GSH content (even in the absence of Cd 2+). Overall, the data indicate that although Cd 2+ exclusion is a powerful mechanism to avoid heavy metal build‐up into photosynthetic organs, the capacity to maintain optimum GSH levels to feed PC biosynthesis could also be an important factor in stress tolerance. 相似文献
6.
The toxicity of Cd 2+in vivo during the early phases of radish ( Raphanus sativus L.) seed germination and the in vitro Cd 2+ effect on radish calmodulin (CaM) were studied. Cd 2+ was taken up in the embryo axes of radish seeds; the increase in fresh weight of embryo axes after 24 h of incubation was inhibited significantly in the presence of 10 mmol m ?3 Cd 2+ in the external medium, when the Cd 2+ content in the embryo axes was c. 1.1 μmol g ?1 FW. The reabsorption of K +, which characterizes germination, was inhibited by Cd 2+, suggesting that Cd 2+ affected metabolic reactivation. The slight effect of Cd 2+ on the transmembrane electric potential of the cortical cells of the embryo axes excluded a generalized toxicity of Cd 2+ at the plasma membrane level. After 24 h of incubation, Cd 2+ induced no increase in total acid-soluble thiols and Cd 2+-binding peptides able to reduce Cd 2+ toxicity. Ca 2+ added to the incubation medium partially reversed the Cd 2+-induced inhibition of the increase in fresh weight of embryo axes and concomitantly reduced Cd 2+ uptake. Equilibrium dialysis experiments indicated that Cd 2+ bound to CaM and competed with Ca 2+ in this binding. Cd 2+ inhibited the activation of Ca 2+-CaM-dependent calf-brain phosphodiesterase, inhibiting the Ca 2+-CaM active complex. Cd 2+ reduced the binding of CaM to the Ca 2+-CaM binding enzymes present in the soluble fraction of the embryo axes of radish seeds. The possibility that Cd 2+ toxicity in radish seed germination is mediated by the action of Cd 2+ on Ca 2+-CaM is discussed in relation to the in vivo and in vitro effects of Cd 2+. 相似文献
7.
Abscisic acid (ABA), a widely known phytohormone involved in the plant response to abiotic stress, plays a vital role in mitigating Cd2+ toxicity in herbaceous species. However, the role of ABA in ameliorating Cd2+ toxicity in woody species is largely unknown. In the present study, we investigated ABA restriction on Cd2+ uptake and the relevance to Cd2+ stress alleviation in Cd2+-hypersensitive Populus euphratica. ABA (5 μM) markedly improved cell viability and growth but reduced membrane permeability in CdCl2 (100 μM)-stressed P. euphratica cells. Moreover, ABA significantly increased the activity of the antioxidant enzymes catalase (CAT), superoxide dismutase (SOD), and ascorbate peroxidase (APX), contributing to the scavenging of Cd2+-elicited H2O2 within P. euphratica cells during the period of CdCl2 exposure (100 μM, 24–72 h). ABA alleviation of Cd2+ toxicity was mainly the result of ABA restriction of Cd2+ uptake under Cd2+ stress. Steady-state and transient flux recordings showed that ABA inhibited Cd2+ entry into Cd2+-shocked (100 μM, 30 min) and short-term-stressed P. euphratica cells (100 μM, 24–72 h). Non-invasive micro-test technique data showed that H2O2 (3 mM) stimulated the Cd2+-elicited Cd2+ influx but that the plasma membrane (PM) Ca2+ channel inhibitor LaCl3 blocked it, suggesting that the Cd2+ influx was through PM Ca2+-permeable channels. These results suggested that ABA up-regulated antioxidant enzyme activity in Cd2+-stressed P. euphratica and that these enzymes scavenged the Cd2+-elicited H2O2 within cells. The entry of Cd2+ through the H2O2-mediated Ca2+-permeable channels was subsequently restricted; thus, Cd2+ buildup and toxicity were reduced in the Cd2+-hypersensitive species, P. euphratica. 相似文献
8.
Cadmium (Cd 2+) is a very toxic metal that causes DNA damage, oxidative stress and apoptosis. Despite many studies, the cellular and molecular mechanisms underlying its high toxicity are not clearly understood. We show here that very low doses of Cd 2+ cause ER stress in Saccharomyces cerevisiae as evidenced by the induction of the unfolded protein response (UPR) and the splicing of HAC1 mRNA. Furthermore, mutant strains (Δ ire1 and Δ hac1) unable to induce the UPR are hypersensitive to Cd 2+, but not to arsenite and mercury. The full functionality of the pathways involved in ER stress response is required for Cd 2+ tolerance. The data also suggest that Cd 2+‐induced ER stress and Cd 2+ toxicity are a direct consequence of Cd 2+ accumulation in the ER. Cd 2+ does not inhibit disulfide bond formation but perturbs calcium metabolism. In particular, Cd 2+ activates the calcium channel Cch1/Mid1, which also contributes to Cd 2+ entry into the cell. The results reinforce the interest of using yeast as a cellular model to study toxicity mechanisms in eukaryotic cells. 相似文献
9.
The aim of this study was to screen a strain for the removal of Cd 2+ from aqueous solution and investigate the characterization and mechanism of the Cd 2+ binding process. A novel strain of yeast showed high tolerance of cadmium, namely Cystobasidium oligophagum QN-3, was isolated from soils, which could resist 22,000 mg/L and 18,000 mg/L Cd 2+ on PDA (potato dextrose agar) plate and in PDA liquid medium, respectively. Cd 2+ binding experiment showed that the strain could remove Cd 2+ from aqueous solution effectively, the maximum Cd 2+ removal rate of 84.45% was achieved at initial Cd 2+ concentration 30 mg/L. Scanning electron microscopy (SEM) analysis revealed that sorption of Cd 2+ by cells could be associated with changes in the cell surface morphology. Fourier transform-infrared spectroscopy (FTIR) analysis confirmed the important role of the functional groups OH, CO, NH 2, COO , PO, and CH on the cell surface in the binding of Cd 2+. The comparison of the binding ability of different cellular parts indicated a significant role of the cell wall played in the Cd 2+ binding process. Pretreatment of the cells by boiling or ultrasonication could improve the biosorption capacity of QN-3. In addition, QN-3 exhibited selective and preferential property of binding capacity for other heavy metals, such as Pb 2+, Cu 2+, Cd 2+, Zn 2+, and Ni 2+. These data suggested the promising use of Cystobasidium oligophagum QN-3 as an effective and friendly biosorbent for cadmium or other heavy metals decontamination in the environment. 相似文献
10.
The effects of CdSO 4 additions on the gene expressions of a mercury reductase, merA, an oxidative stress protein, trxA, the ammonia‐monooxygenase enzyme (AMO), amoA, and the hydroxylamine oxidoreductase enzyme (HAO), hao, were examined in continuously cultured N. europaea cells. The reactor was fed 50 mM NH 4+ and was operated for 78 days with a 6.9 days hydraulic retention time. Over this period, six successive batch additions of CdSO 4 were made with increasing maximum concentrations ranging from 1 to 60 µM Cd 2+. The expression of merA was highly correlated with the level of Cd 2+ within the reactor (Rs = 0.90) with significant up‐regulation measured at non‐inhibitory Cd 2+ concentrations. Cd 2+ appears to target AMO specifically at lower concentrations and caused oxidative stress at higher concentrations, as indicated by the SOURs (specific oxygen uptake rates) and the up‐regulation of trxA. Since Cd 2+ inhibition is irreversible and amoA was up‐regulated in response to Cd 2+ inhibition, it is hypothesized that de novo synthesis of the AMO enzyme occurred and was responsible for the observed recovery in activity. Continuously cultured N. europaea cells were more resistant to Cd 2+ inhibition than previously examined batch cultured cells due to the presence of Mg 2+ and Ca 2+ in the growth media, suggesting that Cd 2+ enters the cell through Mg 2+ and Ca 2+ import channels. The up‐regulation of merA during exposure to non‐inhibitory Cd 2+ levels indicates that merA is an excellent early warning signal for Cd 2+ inhibition. Biotechnol. Bioeng. 2009; 104: 1004–1011. © 2009 Wiley Periodicals, Inc. 相似文献
11.
The ATX1 deletion strain of Saccharomyces cerevisiae is more resistant to Cd 2+ than the wild-type. To investigate the function of Atx1 in Cd 2+ toxicity, we used a metal-binding assay to study the interaction between Atx1 and Cd 2+ in vitro. Using circular dichroism and two-hybrid analyses, we found that Atx1 can bind Cd 2+ specifically and that Cd 2+ binding to Atx1 affects the physical interaction between Atx1 and Ccc2. These results imply that Atx1 delivers Cd 2+ to Ccc2 and that this delivery is, at least in part, responsible for Cd 2+ toxicity in S. cerevisiae. 相似文献
12.
The effects of Cd 2+ and NaCl, applied together or separately, on growth and uptake of Cd 2+ were determined for the halophyte Sesuvium portulacastrum L. Seedlings were cultivated in the presence of 50 or 100 μmol L −1 Cd 2+ alone or combined with 100 or 400 mmol L −1 NaCl. Data showed that alone, Cd 2+ induced chlorosis, necrosis, and inhibited growth. Addition of NaCl to Cd 2+-containing medium restored growth and alleviated the toxicity, however. NaCl also enhanced the amounts of Cd 2+ accumulated in the shoots. All Cd 2+ treatment reduced K + and Ca 2+ uptake and transport to the shoots. Accumulation of Na + in the shoots was not affected by Cd 2+, however. Thus S. portulacastrum maintained its halophytic characteristics in the presence of Cd 2+. We suggest this halophyte could be used for phytoextraction of Cd 2+ from salt-contaminated sites. 相似文献
13.
Pseudomonas aeruginosa CW961, an isolate from the vicinity of a deep-sea hydrothermal vent, grew in the presence of 5 mM Cd 2+ and removed Cd 2+ from solution. Sulfate was sufficient for growth when Cd 2+ was not present in the culture medium; however, thiosulfate was necessary for Cd 2+ precipitation and cell survival in the presence of Cd 2+. 相似文献
14.
A metallothionein-like gene, ThMT3, encoding a type 3 metallothionein, was isolated from a Tamarix hispida leaf cDNA library. Expression analysis revealed that mRNA of ThMT3 was upregulated by high salinity as well as by heavy metal ions, and that ThMT3 was predominantly expressed in the leaf. Transgenic yeast ( Saccharomyces cerevisiae) expressing ThMT3 showed increased tolerance to Cd 2+, Zn 2+, Cu 2+, and NaCl stress. Transgenic yeast also accumulated more Cd 2+, Zn 2+, and NaCl, but not Cu 2+. Analysis of the expression of four genes ( GLR1, GTT2, GSH1, and YCF1) that aid in transporting heavy metal (Cd 2+) from the cytoplasm to the vacuole demonstrated that none of these genes were induced under Cd 2+, Zn 2+, Cu 2+, and NaCl stress in ThMT3-transgenic yeast. H 2O 2 levels in transgenic yeast under such stress conditions were less than half those in control yeast under the same conditions.
Three antioxidant genes ( SOD1, CAT1, and GPX1) were specifically expressed under Cd 2+, Zn 2+, Cu 2+, and NaCl stress in the transgenic yeast. Cd 2+, Zn 2+, and Cu 2+ increased the expression levels of SOD1, CAT1, and GPX1, respectively, whereas NaCl induced the expression of SOD1 and GPX1. 相似文献
15.
A pot-culture experiment was carried out to investigate the effect of arbuscular mycorrhizal (AM) fungus ( Glomus macrocarpum Tul. and Tul.) on plant growth and Cd 2+uptake by Apium graveolens L. in soil with different levels of Cd 2+. Mycorrhizal (M) and non-mycorrhizal (NM) plants were grown in soil with 0, 5, 10, 40 and 80 Cd 2+ mg kg −1soil. The infectivity of the fungus was not affected by the presence of Cd 2+ in the soil. M plants showed better growth and less Cd 2+ toxicity symptoms. Cd 2+ root : shoot ratio was higher in M plants than in NM plants. These differences were more evident at highest Cd 2+ level (80 mg kg −1 soil). Chlorophyll a and chlorophyll b concentrations were significantly higher in AM-inoculated celery leaves. The dilution effect due to increased biomass, immobilization
of Cd 2+ in root and enhanced P-uptake in M plants may be related to attenuation of Cd 2+toxicity in celery. 相似文献
16.
Arginine kinase is closely associated with adaptation to environmental stresses such as high salinity and heavy metal ion levels in marine invertebrates. In this study, the effects of Cd 2+ on the cuttlefish Sepia pharaonis’ arginine kinase (SPAK) were investigated. SPAK was isolated from the muscles of S. pharaonis and upon further purification, showed a single band on SDS-PAGE. Cd 2+ effectively inactivated SPAK, and the double-reciprocal kinetics indicated that Cd 2+ induced non-competitive inhibition of arginine and ATP. Spectrofluorometry results showed that Cd 2+ induced tertiary structure changes in SPAK with the exposure of hydrophobic surfaces that directly induced SPAK aggregation. The addition of osmolytes, glycine, and proline successfully blocked SPAK aggregation and restored the conformation and activity of SPAK. Molecular dynamics simulations involving SPAK and Cd 2+ showed that Cd 2+ partly blocks the entrance of ATP to the active site, and this result is consistent with the experimental results showing Cd 2+-induced inactivation of SPAK. These results demonstrate the effect of Cd 2+ on SPAK enzymatic function and unfolding, including aggregation and the protective effects of osmolytes on SPAK folding. This study provides concrete evidence of the toxicity of Cd 2+ in the context of the metabolic enzyme SPAK, and it illustrates the toxic effects of heavy metals and detoxification mechanisms in cuttlefish. 相似文献
17.
Metallothioneins MTT1 and MTT2 from Tetrahymena thermophila have been characterized. The MTT1 contains mainly characteristic Cys-Cys-Cys and Cys-Cys clusters, but MTT2 contains mainly Cys-X-Cys cluster. Cd 16-MTT1 mainly consists of α-helix and β-turns, in contrast, Cd 11-MTT2 mainly consists of random coils. Reaction of Cd 16-MTT1 and Cd 11-MTT2 with nitric oxide leads to intramolecular disulfide bond formation, respectively. Binding stabilities of Cd 2+, Hg 2+ and Zn 2+ to MTT1 are stronger than those to MTT2. Cu 2+ can not replace Cd 2+ from Cd 16-MTT1 complex, but can replace Cd 2+ from Cd 11-MTT2 complex. The analysis of qRT-PCR revealed MTT2 mRNA levels were 31-fold higher than those of MTT1 under basal conditions. These results further suggest MTT1 possibly play a role in the detoxification of heavy metal ions, and MTT2 may be involved in the homeostasis of copper ions. 相似文献
18.
Summary The interaction of Cd 2+ with the plasma membrane Ca 2+-transporting ATPase of fish gills was studied. ATP-driven Ca 2+-transport in basolateral membrane (BLM) vesicles was inhibited by Cd 2+ with an I
50 value of 3.0 nm at 0.25 m free Ca 2+ using EGTA, HEEDTA and NTA to buffer Ca 2+ and Cd 2+ concentrations. The inhibition was competitive in nature since the K
0.5 value for Ca 2+ increased linearly with increasing Cd 2+ concentrations while the V
max remained unchanged. The Ca 2+ pump appeared to be calmodulin dependent, but we conclude that the inhibition by Cd 2+ occurs directly on the Ca 2+ binding site of the Ca 2+-transporting ATPase and not via the Ca 2+-binding sites of calmodulin. It is suggested that Cd 2+-induced inhibition of Ca 2+-transporting enzymes is the primary effect in the Cd 2+ toxicity towards cells followed by several secondary effects due to a disturbed cellular Ca 2+ metabolism. Our data illustrate that apparent stimulatory effects of low concentrations of Cd 2+ on Ca 2+-dependent enzymes may derive from increased free-Ca 2+ levels when Cd 2+ supersedes Ca 2+ on the ligands. 相似文献
19.
Effects of cadmium cations in free (Cd 2+) and chelated with EDTA (Cd 2+-EDTA) forms were studied on growth, endocytosis, and activity of glutathione S-transferase (GT) in the free-living infusoria Tetrahymena pyriformis. It is shown that the cytotoxicity of Cd 2+ in the free form at a concentration of 10 μM is much higher than of the Cd 2+-EDTA complex at the equimolar concentration. Even at a low concentration (2 μM), Cd 2+ produces an inhibition of the growth rate and endocytosis in the T. pyriformis culture, while the Cd 2+-EDTA complex suppresses these functions insignificantly. Cd 2+ in the free form at concentrations of 10 and 100 μM reduced activity of glutathione S-transferase by 39 and 61%. The chelated
Cd 2+-EDTA complex at these concentrations inhibited the GT activity by 5 and 55%, respectively. 相似文献
20.
Tonoplast, ion antiport activities are critical to ion homeostasis and sequestration in plants. The biochemical properties of these activities, and the enzymes that catalyse them, are little characterized. Here we applied biochemical approaches to study some characteristics and to distinguish between Ca 2+/H + and Cd 2+/H + antiporter activities of tonoplast vesicles from non‐transformed, wild‐type plants. Solubilization and reconstitution of oat‐seedling ( Avena sativa L.) root tonoplast vesicles resulted in about a 6‐fold loss of protein, about a 6‐fold enhancement of Cd 2+/H + antiport specific activity (at 10 µ M Cd 2+), and almost complete loss of Ca 2+/H + antiport activity. Similar results were found for vesicles from mature tobacco ( Nicotiana tabacum) roots. Cd 2+ concentration‐dependent proton efflux was similar and linear with both oat vesicles and proteoliposomes. In contrast, Ca 2+ concentration‐dependent proton efflux of oat vesicles was easily observed while that with proteoliposomes was minimal and non‐linear. Cd 2+ pre‐treatment of oat vesicles reduced verapamil inhibition of Cd 2+/H + activity and verapamil binding to vesicles, while Ca 2+ pre‐treatment was much less protective of Ca 2+/H + activity and verapamil binding. Results show the usefulness of reconstitution, and also inhibitor/ion interaction assays for distinguishing between transporter activities in vitro, but they do not resolve the question of whether there are separate enzymes for Cd 2+/H + and Ca 2+/H +. Our observation that solubilization and reconstitution have similar effects on both Cd 2+/H + and Ca 2+/H + activities of root tonoplast vesicles from immature oat and mature tobacco roots suggests that the transporters involved are similar in young and mature roots, and in roots of different species. 相似文献
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