Hyperaccumulation of cadmium and zinc in Thlaspi caerulescens and Arabidopsis halleri at the leaf cellular level

Vacuolar compartmentalization or cell wall binding in leaves could play a major role in hyperaccumulation of heavy metals. However, little is known about the physiology of intracellular cadmium (Cd) sequestration in plants. We investigated the role of the leaf cells in allocating metal in hyperaccumulating plants by measuring short-term (109)Cd and (65)Zn uptake in mesophyll protoplasts of Thlaspi caerulescens "Ganges" and Arabidopsis halleri, both hyperaccumulators of zinc (Zn) and Cd, and T. caerulescens "Prayon," accumulating Cd at a lower degree. The effects of low temperature, several divalent cations, and pre-exposure of the plants to metals were investigated. There was no significant difference between the Michaelis-Menten kinetic constants of the three plants. It indicates that differences in metal uptake cannot be explained by different constitutive transport capacities at the leaf protoplast level and that plasma and vacuole membranes of mesophyll cells are not responsible for the differences observed in heavy metal allocation. This suggests the existence of regulation mechanisms before the plasma membrane of leaf mesophyll protoplasts. However, pre-exposure of the plants to Cd induced an increase in Cd accumulation in protoplasts of "Ganges," whereas it decreased Cd accumulation in A. halleri protoplasts, indicating that Cd-permeable transport proteins are differentially regulated. The experiment with competitors has shown that probably more than one single transport system is carrying Cd in parallel into the cell and that in T. caerulescens "Prayon," Cd could be transported by a Zn and Ca pathway, whereas in "Ganges," Cd could be transported mainly by other pathways.     

Uptake of Lucifer yellow CH in leaves ofCommelina communis is mediated by endocytosis

Summary Lucifer yellow CH (LY) uptake into intact leaves ofCommelina communis has been studied with conventional fluorescence microscopy as well as confocal laser scanning microscopy. LY, a highly fluorescent tracer for apoplastic transport in plants and fluid phase endocytosis in animal cells, accumulates in the vacuole of leaf cells. However, considerable differences in the ability to take up LY were observed among the various cell types. Mesophyll cells take up large amounts of the dye whereas epidermal cells, including guard and subsidiary cells, showed no fluorescence in their vacuoles. An exception to this are trichome cells which show considerable accumulation of LY. When introduced into the cytoplasm of mesophyll protoplasts ofC. communis by means of a patch-clamp pipette, LY does not enter the vacuole. This supports the contention that exogenous LY can only gain access to the vacuole via endocytosis. Differences in the capacity for LY uptake may therefore reflect differences in endocytotic activity.Abbreviations CLSM Confocal laser scanning microscopy - DIC differential interference contrast - LY Lucifer yellow CH - PM plasma membrane     

Compartmentation and transport of zinc in barley primary leaves as basic mechanisms involved in zinc tolerance

The heavy metal zinc was administered to barley seedlings by increasing its concentration in the hydroponic medium. The most dramatic effect was a severe inhibition of root elongation with little effect on root biomass production. The growth of primary leaves was little affected although the zinc content of the primary leaves increased several-fold. A detailed compartment analysis was performed for 10-d-old barley primary leaves. Under low zinc nutrition (2mmol m ⁻³), highest zinc contents were observed in the cytoplasm of mesophyll protoplasts. At inhibitory zinc concentrations in the hydroponic medium (400 μmol m ⁻³), zinc levels dramatically and preferentially increased in the apoplastic space. Elevated zinc levels were also observed in the epidermal cells, and to a lesser extent, in mesophyll vacuoles. The cytoplasmic content of mesophyll protoplasts was unchanged, indicating perfect zinc homeostasis within the leaf. In order to understand the transport mechanisms underlying the steady-state distribution profile, we used ⁶⁵Zn to conduct uptake experiments with leaves whose lower epidermis had been stripped. The leaves were placed on zinc solutions of varying concentrations containing ⁶⁵Zn for 5 min to 6 h. After the incubation, the leaves were fractionated into mesophyll and epidermis protoplasts and residue, the latter mainly representing cell wall. Adsorption of Zn to the extracellular matrix was 100 times faster than Zn uptake into the cells. By far the largest portion taken up into the mesophyll protoplasts rapidly appeared in the vacuolar compartment. These results demonstrate the importance of compartmentation and transport as homeostatic mechanisms within the leaves to handle high, possibly toxic, zinc levels in the shoot.     

Differential ion accumulation and ion fluxes in the mesophyll and epidermis of barley

In barley (Hordeum vulgare L.) leaves, differential ion accumulation commonly results in inorganic phosphate (Pi) being confined to the mesophyll and Ca(2+) to the epidermis, with preferential epidermal accumulation of Cl(-), Na(+), and some other ions. The pattern was confirmed in this study for major inorganic anions and cations by analysis of barley leaf protoplasts. The work focused on the extent to which differences in plasma membrane ion transport processes underlie these observations. Ion transport across the plasma membrane of barley epidermal and mesophyll protoplasts was investigated electrophysiologically (by microelectrode impalement and patch clamping) and radiometrically. Data from both approaches suggested that similar types of ion-selective channels and membrane transporters, which catalyze the transport of Ca(2+), K(+), Na(+), and Pi, exist in the plasma membrane of the two cell types. In general, the simple presence or absence of ion transporters could not explain cell-type-specific differences in ion accumulation. However, patch-clamp data suggested that differential regulation of instantaneously activating ion channels in the plasma membrane could explain the preferential accumulation of Na(+) in the epidermis.     

Cadmium and zinc flux in wild-type and cadmium-resistant CHO cells

Cellular flux of cadmium-109 and zinc-65 is characterized in cultured Chinese hamster ovary cells. The transport of cadmium is primarily unidirectional and, following uptake, cadmium is strongly retained. Zinc transport is bidirectional and intracellular zinc continuously leaches out into the medium. Nonradioactive cadmium or zinc enhances the efflux of⁶⁵Zn from prelabeled cells. Transport of these metals into wild-type cells is not affected by azide, ouabain, cycloheximide, or actinomycin D. A cadmium-resistant mutant was isolated that exhibited altered sensitivities to certain inhibitors of macromolecular synthesis as well as quantitative differences in metal transport and accumulation. Although the mutant accumulates less cadmium than the wild-type cell, that which is retained is bound much more tightly. In addition, this lower rate of cadmium uptake is significantly decreased by either cycloheximide or actinomycin D. This suggests that thede novo synthesis of a protein or proteins is required for much of the net cadmium retention by the cadmium-resistant cells.     

Processes modulating calcium distribution in citrus leaves. An investigation using x-ray microanalysis with strontium as a tracer

Citrus leaves accumulate large amounts of calcium that must be compartmented effectively to prevent stomatal closure by extracellular Ca2+ and interference with Ca(2+)-based cell signaling pathways. Using x-ray microanalysis, the distribution of calcium between vacuoles in different cell types of leaves of rough lemon (Citrus jambhiri Lush.) was investigated. Calcium was accumulated principally in palisade, spongy mesophyll, and crystal-containing idioblast cells. It was low in epidermal and bundle sheath cells. Potassium showed the reverse distribution. Rubidium and strontium were used as tracers to examine the pathways by which potassium and calcium reached these cells. Comparisons of strontium and calcium distribution indicated that strontium is a good tracer for calcium, but rubidium did not mirror the potassium distribution pattern. The amount of strontium accumulated was highest in palisade cells, lowest in bundle sheath and epidermal cells, and intermediate in the spongy mesophyll. Accumulation of strontium in palisade and spongy mesophyll was accompanied by loss of potassium from these cells and its accumulation in the bundle sheath. Strontium moved apoplastically from the xylem to all cell types, and manipulation of water loss from the adaxial leaf surface suggested that diffusion is responsible for strontium movement to this side of the leaf. The results highlight the importance of palisade and spongy mesophyll as repositories for calcium and suggest that calcium distribution between different cell types is the result of differential rates of uptake. This tracer technique can provide important information about the ion uptake and accumulation properties of cells in intact leaves.     

Displacement of frequently occurring heacy metals in autumn leaves of beech (Fagus sylvatica)

Summary By utilizing energy-dispersive X-ray microanalysis the heavy metals manganese, iron, zinc and lead were determined in different tissues of beech (Fagus sylvatica L.) autumn leaves. It was observed that all four metals were accumulated in sieve element-companion cell complexes of the leaf veins in the period from the green (2 October) to the brown (23 October) leaf coloration. Concomitantly, the concentration of these metals decreased in certain tissues of the stems subtending the leaves. The major reservoirs of heavy metals in the stems were periderm, cortex, pith and xylem rays. Since sieve element-companion cell complexes of the stems showed increasing metal concentrations during the transition from the green to the brown leaf stage, and since this temporary increase also occurred in the petiole phloem, it is inferred that symplastic transport can be used in addition to apoplastic transport for the displacement of heavy metals. It is assumed that the accumulation of heavy metals in the veins of autumn leaves indicates the deposition of surplus ions which are excluded when leaves are cast off.Supported by Deutsche Forschungsgemeinschaft and by Bundesministerium für Forschung und Technologie, Federal Republic of Germany, Grant PBE 373607.     

Mechanisms of chloride partitioning in the leaves of salt-stressed Sorghum bicolor L.

Chloride transport in sheath and blade tissue and the cellular distribution of Cl^- were investigated in an attempt to determine the physiological basis of the preferential accumulation of Cl^- in sheaths of salt-stressed sorghum ( Sorghum bicolor L.). Import and export of ³⁶Cl^- in leaf sheaths and blades of intact sorghum were followed over a 2 week period. X-ray microanalysis of frozen-hydrated bulk tissue samples was used to determine the accumulation of Cl^- and other elements in the vacuoles of sheath and blade cells.
Sheath tissue accumulated Cl^- despite a relatively high Cl^- turnover rate. Chloride was shown to accumulate in most cell types of the sheath, particularly in adaxial epidermal cells. After an initial increase in the concentration of Cl^-, blade tissue regulated Cl^- levels within certain limits. Chloride levels in blades were greater in the abaxial and adaxial epidermal cells than in other cell types. The epidermal cells of blades accumulated Cl^- to approximately the same concentration as sheath epidermal cells. The Cl^- concentration in the photosynthetically active mesophyll and bundle sheath cells, however, remained low.
Thus, the partitioning of Cl^- previously observed in the leaves of salinized sorghum apparently results from the ability of bundle sheath and mesophyll cells to maintain concentrations of Cl^- at lower levels than do epidermal cells. In addition, the relatively large sheath parenchyma cells tend to serve as reservoirs for the storage of Cl^-.     

Increased cysteine availability is essential for cadmium tolerance and accumulation in Arabidopsis thaliana

Employing genetic transformation using an Atcys-3A cDNA construct expressing the cytosolic O-acetylserine(thiol)lyase (OASTL), we obtained two Arabidopsis lines with different capabilities for supplying cysteine under metal stress conditions. Lines 1-2 and 10-10, grown under standard conditions, showed similar levels of cysteine and glutathione (GSH) to those of the wild-type. However, in the presence of cadmium, line 10-10 showed significantly higher levels. The increased thiol content allowed line 10-10 to survive under severe heavy metal stress conditions (up to 400 microm of cadmium in the growth medium), and resulted in an accumulation of cadmium in the leaves to a level similar to that of metal hyperaccumulator plants. Investigation of the epidermal leaf surface clearly showed that most of the cadmium had accumulated in the trichomes. Furthermore, line 10-10 was able to accumulate more cadmium in its trichomes than the wild-type, whereas line 1-2 showed a reduced capacity for cadmium accumulation. Our results suggest that an increased rate of cysteine biosynthesis is responsible for the enhanced cadmium tolerance and accumulation in trichome leaves. Thus, molecular engineering of the cysteine biosynthesis pathway, together with modification of the number of leaf trichomes, may have considerable potential in increasing heavy metal accumulation for phytoremediation purposes.     

Investigation of heavy metal hyperaccumulation at the cellular level: development and characterization of Thlaspi caerulescens suspension cell lines

The ability of Thlaspi caerulescens, a zinc (Zn)/cadmium (Cd) hyperaccumulator, to accumulate extremely high foliar concentrations of toxic heavy metals requires coordination of uptake, transport, and sequestration to avoid damage to the photosynthetic machinery. The study of these metal hyperaccumulation processes at the cellular level in T. caerulescens has been hampered by the lack of a cellular system that mimics the whole plant, is easily transformable, and competent for longer term studies. Therefore, to better understand the contribution of the cellular physiology and molecular biology to Zn/Cd hyperaccumulation in the intact plant, T. caerulescens suspension cell lines were developed. Differences in cellular metal tolerance and accumulation between the cell lines of T. caerulescens and the related nonhyperaccumulator, Arabidopsis (Arabidopsis thaliana), were examined. A number of Zn/Cd transport-related differences between T. caerulescens and Arabidopsis cell lines were identified that also are seen in the whole plant. T. caerulescens suspension cell lines exhibited: (1) higher growth requirements for Zn; (2) much greater Zn and Cd tolerance; (3) enhanced expression of specific metal transport-related genes; and (4) significant differences in metal fluxes compared with Arabidopsis. One interesting feature exhibited by the T. caerulescens cell lines was that they accumulated less Zn and Cd than the Arabidopsis cell lines, most likely due to a greater metal efflux. This finding suggests that the T. caerulescens suspension cells represent cells of the Zn/Cd transport pathway between the root epidermis and leaf. We also show it is possible to stably transform T. caerulescens suspension cells, which will allow us to alter the expression of candidate hyperaccumulation genes and thus dissect the molecular and physiological processes underlying metal hyperaccumulation in T. caerulescens.     

Stress-dependent redistribution of abscisic acid (ABA) in Hordeum vulgare L leaves: the role of epidermal ABA metabolism, tonoplastic transport and the cuticle

When ¹⁴C-labelled abscisic acid ([¹⁴C]ABA) was supplied to isolated protoplasts of the barley leaf at pH 6, initial rates of metabolism were about five times higher in epidermal cell protoplasts than in mesophyll cell protoplasts if equal cytosolic volumes were considered. In spite of the fact that epidermal cells make up only about 35% of the total water space in barley leaves, and despite the small cytosolic volume of these cells, in intact leaves all epidermal cells would thus metabolize half as much ABA per unit time as the mesophyll cells (0–27 and 0–51 mmol h^?1 m^?3 leaf water). Therefore, under these conditions epidermal cells seem to be a stronger sink than mesophyll cells for ABA that arrives via the transpiration stream. However, at an apoplastic pH of 7–25, which occurs in stressed leaves, the proportion of total metabolized ABA would be much smaller in epidermal than in mesophyll cells (0–029 and 0–204 mmolh^?l m^?3 leaf water). Our results indicate that under conditions of slightly alkaline apoplastic pH the epidermis may serve as the main source for fast stress-dependent ABA redistribution into the guard cell apoplast. This is partly the result of ABA transport across the epidermal tonoplast, which is dependent on the apoplastic pH and possibly on the cytosolic calcium concentration. The cuticle seems to be of no particular importance in stress-induced apoplastic ABA shifts and cannot be regarded as a significant sink for high ABA concentrations under stress.     

The role of zinc transporters in cadmium and manganese transport in mammalian cells

To understand the mechanism of cadmium accumulation, it is important to know the precise mechanisms of transport systems for other metals. Recently, utilization of genomics and metallomics has clarified the involvement of specific metal transporter(s) in cadmium uptake. Studies with metallothionein (MT)-null cadmium-resistant cells have revealed the involvement of the manganese/zinc transport system in cadmium uptake. Genomic studies of strain differences in sensitivity to cadmium-induced testicular hemorrhage revealed that a zinc transporter, Zrt-, Irt-related protein (ZIP) 8 encoded by slc39a8, is responsible for the strain difference. Ectopic expression of ZIP8 in various cells enhanced the uptake of cadmium, manganese, and zinc. ZIP8-transgenic mice showed high expression of ZIP8 in the vasculature of testis and apical membrane of proximal tubules in kidney, and exhibited enhanced cadmium accumulation and toxicity when treated with cadmium. The expression of ZIP8 was found to be down-regulated in MT-null cadmium-resistant cells, in which the uptake rates of both cadmium and manganese were decreased. These data suggest that ZIP8 plays an important role in the uptake of both cadmium and manganese in mammalian cells. The role of ZIP14 in the uptake of cadmium and manganese is also discussed.     

Viability and release of complexing compounds during accumulation of heavy metals by a brewer's yeast

Saccharomyces cerevisiae NCYC 1190 cells accumulated (after 1 h) lead and cadmium at similar levels, and to a lesser degree also copper. During heavy metal accumulation, there was a considerable loss of viability of copper-treated cells (about 99% in the first 20 min of contact with the metal), and a less pronounced lethal effect on cadmium- and lead-treated cells (about 66% and 46% after 1 h of contact with cadmium or lead, respectively) was detected. During copper accumulation, a leakage of UV-absorbing compounds and inorganic phosphate was observed; this did not occur with lead, whereas with cadmium a small amount of leakage of inorganic phosphate was detected. The filtrates of copper-treated cells contained copper-binding molecules. The copper-binding capacity of the filtrates increased with time according to the release of inorganic phosphate and UV-absorbing compounds. These compounds can bind an appreciable quantity of metal ions, making them unavailable for cell uptake and thus reducing the efficiency of heavy metals removal by yeast cells.     

Leaf-targeted phytochelatin synthase in Arabidopsis thaliana

One of the key steps in developing transgenic plants for the phytoremediation of metal containing soils is to develop plants that accumulate metals in the aerial tissues. With the goal of changing the distribution of phytochelatin (PC)-dependent cadmium accumulation from roots to the leaves, the phytochelatin synthase (PCS) deficient cad1-3 mutant and wild type (Col-0) Arabidopsis plants were transformed with an Arabidopsis phytochelatin synthase (AtPCS1) under the control of a leaf-specific promoter. Three independent transformant lines from each genetic background were chosen for further analysis and designated cad-PCS and WT-PCS. PCS activity in the cadPCS lines was restored in the leaves, but not in the roots. Additionally, when whole plants were treated with cadmium, PCs were found only in the leaves of cad-PCS plants. Although the inserted AtPCS1 gene was leaf-specific, cad-PCS lines showed an overall decrease in cadmium toxicity evidenced by a partial amelioration of the "brown-root" phenotype and root growth was restored to wild type levels when treated with cadmium and arsenate. WT-PCS lines showed an increase in leaf PCS activity but had only wild type PC levels. In addition, cadmium uptake studies indicated that there was no difference in cadmium accumulation among all types tested. So, while we were able to protect the plants against cadmium by expressing PC synthase only in the leaves, we were not able to limit cadmium accumulation to aerial tissues.     

Zinc compartmentation in root, transport into xylem, and absorption into leaf cells in the hyperaccumulating species of Sedum alfredii Hance

Sedum alfredii Hance can accumulate Zn in shoots over 2%. Leaf and stem Zn concentrations of the hyperaccumulating ecotype (HE) were 24- and 28-fold higher, respectively, than those of the nonhyperaccumulating ecotype (NHE), whereas 1.4-fold more Zn was accumulated in the roots of the NHE. Approximately 2.7-fold more Zn was stored in the root vacuoles of the NHE, and thus became unavailable for loading into the xylem and subsequent translocation to shoot. Long-term efflux of absorbed ⁶⁵Zn indicated that ⁶⁵Zn activity was 6.8-fold higher in shoots but 3.7-fold lower in roots of the HE. At lower Zn levels (10 and 100 μM), there were no significant differences in ⁶⁵Zn uptake by leaf sections and intact leaf protoplasts between the two ecotypes except that 1.5-fold more ⁶⁵Zn was accumulated in leaf sections of the HE than in those of the NHE after exposure to 100 μM for 48 h. At 1,000 μM Zn, however, approximately 2.1-fold more Zn was taken up by the HE leaf sections and 1.5-fold more ⁶⁵Zn taken up by the HE protoplasts as compared to the NHE at exposure times >16 h and >10 min, respectively. Treatments with carbonyl cyanide m-chlorophenylhydrazone (CCCP) or ruptured protoplasts strongly inhibited ⁶⁵Zn uptake into leaf protoplasts for both ecotypes. Citric acid and Val concentrations in leaves and stems significantly increased for the HE, but decreased or had minimal changes for the NHE in response to raised Zn levels. These results indicate that altered Zn transport across tonoplast in the root and stimulated Zn uptake in the leaf cells are the major mechanisms involved in the strong Zn hyperaccumulation observed in S. alfredii H.     

Functional expression of a bacterial heavy metal transporter in Arabidopsis enhances resistance to and decreases uptake of heavy metals

Large parts of agricultural soil are contaminated with lead (Pb) and cadmium (Cd). Although most environments are not heavily contaminated, the low levels observed nonetheless pose a high risk of heavy metal accumulation in the food chain. Therefore, approaches to develop plants with reduced heavy metal uptake are important. Recently, many transgenic plants with increased heavy metal resistance and uptake of heavy metals were developed for the purpose of phytoremediation. However, to reduce heavy metal in the food chain, plants that transfer less heavy metals to the shoot are required. We tested whether an Escherichia coli gene, ZntA, which encodes a Pb(II)/Cd(II)/Zn(II) pump, could be useful for developing plants with reduced heavy metal content. Yeast cells transformed with this gene had improved resistance to Pb(II) and Cd(II). In Arabidopsis plants transformed with ZntA, ZntA was localized at the plasma membrane and improved the resistance of the plants to Pb(II) and Cd(II). The shoots of the transgenic plants had decreased Pb and Cd content. Moreover, the transgenic protoplasts showed lower accumulation of Cd and faster release of preloaded Cd than wild-type protoplasts. These results show that a bacterial transporter gene, ZntA, can be functionally expressed in plant cells, and that that it may be useful for the development of crop plants that are safe from heavy metal contamination.     

Heavy metal uptake by intact cells and protoplasts of Aureobasidium pullulans

Protoplasts prepared from yeast-like cells, hyphae and chlamydospores of Aureobasidium pullulans can take up heavy metals such as Zn²⁺, Co²⁺, Cd²⁺ and Cu²⁺. In relation to intact cells, the sensitivity of protoplasts to Cu²⁺ and Cd²⁺ was increased although chlamydospore protoplasts were more tolerant than yeast-like cell protoplasts. Surface binding of metals was reduced in protoplasts as compared with intact cells and this reduction was particularly evident for chlamydospore protoplasts. At the highest concentrations used, uptake of Zn²⁺, Co²⁺ and Cd²⁺ by yeast-like cell protoplasts was greater than that observed in intact cells which may have been due to toxicity, especially for Cd²⁺, resulting in increased membrane permeability, though for Zn²⁺ and Co²⁺ some barrier effect of the cell wall could not be completely discounted. Chlamydospore protoplasts were capable of intracellular metal uptake, unlike intact chlamydospores, and for Zn²⁺, uptake appeared to be via a different system less specific than that of the other cell types. For chlamydospores, the use of protoplasts confirmed the importance of the cell wall in preventing entry of metal ions into the cell.     

Distribution of cadmium in leaves of Thlaspi caerulescens

Knowledge of the intracellular distribution of Cd in leaves is necessary in order to understand the mechanisms of hyperaccumulation in Thlaspi caerulescens. Ganges and Prayon, two ecotypes accumulating Cd to different levels, were grown in nutrient medium containing varying concentrations (0, 5, 10, 50, and 100 microM) of Cd. Several different approaches were combined in this study to (i) validate the results obtained by a specific method and (ii) establish the link between observations and measurements performed at different scales. In both ecotypes, Cd, localized by autoradiography, was found mainly at the edges of the leaves, but also in points of higher concentration spread over the whole limb surface. This localization was clearly correlated with the necrotic spots observed on Prayon leaves. Scanning electron microscopy coupled with energy dispersive X-ray microanalysis (cryo-SEM-EDXMA) and tissue fractionation (apoplasm, cell walls, mesophyll protoplasts, and lower epidermis) showed that Cd had similar patterns of distribution in leaf cells of both ecotypes. Cadmium was found both inside the cells and in the cell walls, mainly in the large epidermal cells but also in small epidermal cells. All the methods used agreed well and the results indicated that metal storage in the plants studied involves more than one compartment and that Cd is stored principally in the less metabolically active parts of leaf cells.     

锰对植物毒害及植物耐锰机理研究进展

含锰矿渣的排放造成了严重的土壤锰污染。揭示锰毒害和植物的耐锰机制对于污染土壤治理具有重要意义。研究表明,高浓度的Mn2＋能够抑制根系Ca2＋、Fe2＋和Mg2＋等元素的吸收及活性,引起氧化性胁迫导致氧化损伤,使叶绿素和Rubisco含量下降、叶绿体超微结构破坏和光合速率降低。而锰超累积植物则具有多种解毒或耐性机制,如区域化、有机酸螯合、外排作用、抗氧化作用和离子交互作用等。根系主要通过有机酸的螯合作用促进植物对Mn^2＋的转运解毒,同时能够将过量的Mn^2＋区域化在根细胞壁中;叶片可通过酚类物质或有机酸螯合Mn^2＋,并将其区域化在叶片表皮细胞和叶肉细胞的液泡中（或通过表皮毛将Mn^2＋排出体外）。其中,金属转运蛋白在植物对Mn^2＋的吸收、转运、累积和解毒过程中发挥着重要作用。