Recognition of dominant attractants by key chemoreceptors mediates recruitment of plant growth-promoting rhizobacteria

Chemotaxis to plant root exudates is supposed to be a prerequisite for efficient root colonization by rhizobacteria. This is a highly multifactorial process since root exudates are complex compound mixtures of which components are recognized by different chemoreceptors. Little information is available as to the key components in root exudates and their receptors that drive colonization related chemotaxis. We present here the first global assessment of this issue using the plant growth-promoting rhizobacterium (PGPR) Bacillus velezensis SQR9 (formerly B. amyloliquefaciens). This strain efficiently colonizes cucumber roots, and here, we show that chemotaxis to cucumber root exudates was essential in this process. We conducted chemotaxis assays using cucumber root exudates at different concentrations, individual exudate components as well as recomposed exudates, taking into account their concentrations detected in root exudates. Results indicated that two key chemoreceptors, McpA and McpC, were essential for root exudate chemotaxis and root colonization. Both receptors possess a broad ligand range and recognize most of the exudate key components identified (malic, fumaric, gluconic and glyceric acids, Lys, Ser, Ala and mannose). The remaining six chemoreceptors did not contribute to exudate chemotaxis. This study provides novel insight into the evolution of the chemotaxis system in rhizobacteria.     

Root exudate cocktails: the link between plant diversity and soil microorganisms?

Higher plant diversity is often associated with higher soil microbial biomass and diversity, which is assumed to be partly due to elevated root exudate diversity. However, there is little experimental evidence that diversity of root exudates shapes soil microbial communities. We tested whether higher root exudate diversity enhances soil microbial biomass and diversity in a plant diversity gradient, thereby negating significant plant diversity effects on soil microbial properties. We set up plant monocultures and two‐ and three‐species mixtures in microcosms using functionally dissimilar plants and soil of a grassland biodiversity experiment in Germany. Artificial exudate cocktails were added by combining the most common sugars, organic acids, and amino acids found in root exudates. We applied four different exudate cocktails: two exudate diversity levels (low‐ and high‐diversity) and two nutrient‐enriched levels (carbon‐ and nitrogen‐enriched), and a control with water only. Soil microorganisms were more carbon‐ than nitrogen‐limited. Cultivation‐independent fingerprinting analysis revealed significantly different soil microbial communities among exudate diversity treatments. Most notably and according to our hypothesis, adding diverse exudate cocktails negated the significant plant diversity effect on soil microbial properties. Our findings provide the first experimental evidence that root exudate diversity is a crucial link between plant diversity and soil microorganisms.     

根分泌物对根际难溶性镉的活化作用及对水稻吸收、运输镉的影响

采用人工控制光温条件的蛭石－营养液相结合的培养方法,对根分泌物活化难溶性硫化镉以及对水稻吸收、运输镉的影响进行了研究。结果表明,缺铁水稻根分泌物和缺铁小麦根分泌匀能活化水稻根际的难溶性镉（ＣｄＳ）,促进了水稻对这部分镉的吸收和运输;但二者的活化强度不同,缺铁小麦根分泌物对镉的活化作用较缺铁水稻根分泌物强。     

Mobilization of cadmium and other metals from two soils by root exudates of Zea mays L., Nicotiana tabacum L. and Nicotiana rustica L.

Soluble root exudates were collected from three plants (Nicotiana tabacum L., Nicotiana rustica L. and Zea mays L.), grown under axenic and hydroponic conditions, in order to study their metal-solubilizing ability for Cd and other cations (Cu, Fe, Mn, Ni, Zn). Nicotiana spp. and Zea mays L. root exudates differed markedly in C/N ratio, sugars vs. amino acids ratio and organic acids content. Metals from two soils were extracted with either root exudate solutions, containing equal amounts of organic carbon, or distilled water as control. In the presence or absence of root exudates, the solubility of Fe and Mn was much higher than of the four other metals tested. Root exudates increased the solubilities of Mn and Cu, whereas those of Ni and Zn were not affected. Root exudates of Nicotiana spp. enhanced the solubility of Cd. The extent of Cd extraction by root exudates (N. tabacum L. N. rustica L. Zea mays L.) was similar to the order of Cd bioavailability to these three plants when grown on soil. An increase in Cd solubility in the rhizosphere of apical root zones due to root exudates is likely to be an important cause of the relatively high Cd accumulation in Nicotiana spp.     

Effects of selected root exudate components on soil bacterial communities

Low-molecular-weight organic compounds in root exudates play a key role in plant-microorganism interactions by influencing the structure and function of soil microbial communities. Model exudate solutions, based on organic acids (OAs) (quinic, lactic, maleic acids) and sugars (glucose, sucrose, fructose), previously identified in the rhizosphere of Pinus radiata, were applied to soil microcosms. Root exudate compound solutions stimulated soil dehydrogenase activity and the addition of OAs increased soil pH. The structure of active bacterial communities, based on reverse-transcribed 16S rRNA gene PCR, was assessed by denaturing gradient gel electrophoresis and PhyloChip microarrays. Bacterial taxon richness was greater in all treatments than that in control soil, with a wide range of taxa (88-1043) responding positively to exudate solutions and fewer (<24) responding negatively. OAs caused significantly greater increases than sugars in the detectable richness of the soil bacterial community and larger shifts of dominant taxa. The greater response of bacteria to OAs may be due to the higher amounts of added carbon, solubilization of soil organic matter or shifts in soil pH. Our results indicate that OAs play a significant role in shaping soil bacterial communities and this may therefore have a significant impact on plant growth.     

植物根系分泌物在污染及沙化土壤修复中的应用现状与前景

近年来重金属污染等生态环境问题日益受到重视,而物理、化学修复方法存在的诸如成本高、二次污染等问题,使得利用植物、微生物等进行联合治理成为环境修复的重要手段。植物根系分泌物作为植物与土壤进行营养和信息交流的重要媒介,不但对植物的生长具有重要作用,其在污染及沙化土壤修复中作用的研究也得以广泛开展。本文对根系分泌物的组成、分泌机制进行了阐述,并对其在植物吸收重金属、化感作用、植物根系与根际微生物互作、改变土壤理化性质等过程中的作用及机理进行了总结。此外,本文还对利用根系分泌物和根际微生物在生态环境治理中的应用现状、面临的难题及未来的发展等进行了讨论。希望本文可为基于植物与微生物进行的环境修复技术的实际应用提供理论支撑。     

富钾基因型籽粒苋主要根系分泌物及其对土壤矿物态钾的活化作用

通过试验,研究了2种供K水平对籽粒苋(Amaranthus spp.)富K基因型和一般基因型根系分泌物含量变化的影响,以及在低K胁迫时3个生长期两类基因型主要根系分泌物含量的变化特点,模拟了籽粒苋根系分泌物对土壤矿物态钾的活化作用.结果表明,籽粒苋根系分泌物中可溶性糖、氨基酸和有机酸含量随供K水平的升高而降低,且富K基因型根系分泌物中3种物质的分泌量始终大于一般基因型;在正常供K条件下,两基因型根系分泌能力相近,但在低K处理时,前者显著高于后者,差异显著;在2种供K水平下,根系有机酸分泌量在3种分泌物中占绝对优势,分别是可溶性糖和氨基酸分泌量的几十倍和几百倍.籽粒苋生长到50 d时,一般基因型根系可溶性糖、氨基酸和有机酸的分泌量较40 d时迅速降低.富K基因型根系分泌物中可溶性糖、氨基酸和有机酸含量在3个生长时期均大于一般基因型,且随着生长时间的延长,两基因型间可溶性糖、氨基酸和有机酸含量的差异明显增大.两类基因型在3个生长时期均以分泌有机酸为主,其占总分泌量的93%以上.籽粒苋根系分泌物处理后的土壤速效钾含量均高于清水对照处理,富K基因型在低K胁迫时的根系分泌物对土壤K的活化作用明显大于一般基因型.     

Role of rhizosphere mechanisms in Cd uptake by various wheat cultivars

In each wheat type, cultivars have different propensities to accumulate Cd in their grains, likely depending on Cd uptake by roots and/or Cd distribution in the plant. This study investigates the processes in the root–soil interface and their role in high or low grain Cd accumulation. Twenty-four cultivars of spring bread, winter bread, durum, and spelt wheat with different grain Cd accumulation levels were investigated regarding removal of Cd from soil, pH, Cd and organic acids in root exudates, and cation-exchange capacity of roots (rootCEC). In addition, we investigated ¹⁰⁹Cd uptake from a nutrient solution resembling soil solution. The removal of Cd from the rhizosphere soil increased, likely due to increased rootCEC with increased grain Cd accumulation propensity, except in spring bread wheat. The ¹⁰⁹Cd uptake from solution did not differ between high and low grain Cd accumulators. If the soil Cd concentration was elevated, rootCEC increased, as did pH, and succinic acid levels in the exudates, while lactic and citric acid levels in root exudates decreased. This work indicates that high grain Cd accumulators take up more Cd from soil than do low accumulators. But not by a different capacity to take up Cd from soil solution. The higher rootCEC in high accumulating cultivars may influence the release of Cd from the soil particles.     

Increasing flavonoid concentrations in root exudates enhance associations between arbuscular mycorrhizal fungi and an invasive plant

Many invasive plants have enhanced mutualistic arbuscular mycorrhizal (AM) fungal associations, however, mechanisms underlying differences in AM fungal associations between introduced and native populations of invasive plants have not been explored. Here we test the hypothesis that variation in root exudate chemicals in invasive populations affects AM fungal colonization and then impacts plant performance. We examined flavonoids (quercetin and quercitrin) in root exudates of native and introduced populations of the invasive plant Triadica sebifera and tested their effects on AM fungi and plant performance. We found that plants from introduced populations had higher concentrations of quercetin in root exudates, greater AM fungal colonization and higher biomass. Applying root exudates more strongly increased AM fungal colonization of target plants and AM fungal spore germination when exudate donors were from introduced populations. The role of root exudate chemicals was further confirmed by decreased AM fungal colonization when activated charcoal was added into soil. Moreover, addition of quercetin into soil increased AM fungal colonization, indicating quercetin might be a key chemical signal stimulating AM fungal associations. Together these results suggest genetic differences in root exudate flavonoids play an important role in enhancing AM fungal associations and invasive plants’ performance, thus considering root exudate chemicals is critical to unveiling mechanisms governing shifting plant-soil microbe interactions during plant invasions.Subject terms: Population dynamics, Community ecology, Plant ecology     

Evaluation of a novel tool for sampling root exudates from soil-grown plants compared to conventional techniques

The release of low molecular weight (LMW) organic compounds (e.g. organic acids, amino acids, sugars, etc.) by living plant roots significantly contributes to the development of chemical, physical as well as microbial rhizosphere gradients. Suitable and accurate sampling procedures are crucial for enhancing our understanding of the dynamics of related rhizosphere processes. Here we compare common sampling techniques with a novel tool for root exudate collection that allows non-destructive and repetitive sampling from soil-grown roots. Root exudates from Zea mays L. were collected using the following techniques: (i) hydroponic growth and sampling, (ii) soil growth and hydroponic sampling and (iii) rhizoboxes fitted with a novel in situ root exudate collecting tool. Furthermore, rhizosphere soil solution for the analysis of exudates and microbial metabolites was sampled using micro-suction cups (iv). The effect of different sampling solutions (deionised water and 0.5 mM CaCl₂) on organic acid and amino acid exudation patterns was also investigated. The novel exudate collecting tool was successfully tested for root exudate sampling. Results showed that particularly amino acid exudation rates were significantly affected by growth conditions and sampling procedures, while organic acid exudation patterns varied less across the different sampling setups. Despite qualitative and quantitative differences, exudation rates were in the same order of magnitude across the different sampling procedures. Soil solution concentrations obtained from micro-suction-cup sampling at defined distance to the root surface showed no distinct gradient, highlighting the importance of soil microorganisms in regulating the soil solution concentration of LMW C compounds either via microbial degradation or the release of microbial metabolites. The exudate collector offers new opportunities to assess root exudation rates and composition from soil-grown plants and thus enhances our knowledge of fundamental rhizosphere processes.     

根分泌作用与植物对金属毒害的抗性

在金属污染进入体内之前将其有效性和毒性降低是植物的主要抗金属机制之一,根系是金属等土壤污染物进入植物的门户,它能分泌有机酸、氨基酸,糖、生长物质等根分泌物与根际环境,根分泌物在植物吸收金属的过程中影响很大,它们可以通过改变根球环境的ＰＨ、Ｅｈ等物理、化学性质而影响根系对金属的吸收;通过螯合、络合,沉淀等作用将金属污染物滞留于根外;通过改变根际微生的组织,活性和分泌作用而改变根际环境中金属的数量和活     

秋茄(Kandelia candel (L))根系分泌低分子量有机酸及其对重金属生物有效性的影响

应用电感耦合等离子体质谱(ICP-Ms)与高效液相色谱(HPLC)分别对福建漳江口红树林湿地不同土壤结构(砂质与泥质)根际与非根际沉积物中重金属(Cu,Pb,Cd,Zn)含量,以及生长于砂质与泥质滩涂上的红树植物秋茄(Kandelia candel(L)Druce))幼苗根系分泌物中的低分子量有机酸进行测定。在室内模拟秋茄根系分泌的低分子量有机酸,作为重金属提取剂提取沉积物中可溶解态与碳酸盐结合态重金属,并与欧盟标准物质局(BCR)连续提取法相比较,探讨红树根系分泌的低分子量有机酸对红树林沉积物重金属生物有效性的影响。研究结果表明:漳江口红树林泥质沉积物中重金属含量大于砂质沉积物,根际沉积物大于非根际沉积物。两样地沉积物中重金属的赋存形态主要以铁锰氧化物结合态为主,根际沉积物中可交换态与碳酸盐结合态重金属含量均大于非根际沉积物。秋茄根系分泌低分子量有机酸为甲酸,丁酸,苹果酸,柠檬酸,乳酸。不同土壤结构对秋茄根系分泌的苹果酸,柠檬酸,乳酸有显著影响(P<0.05)。以低分子量有机酸作为提取剂对沉积物中可溶解态与碳酸盐结合态重金属的提取率表现为:柠檬酸>混合酸>苹果酸>乳酸>乙酸,低分子量有机酸对红树林沉积物重金属的生物有效性有促进作用。     

Biochemical Changes in Root Exudate and Xylem Sap of Tomato Plants Infected with Meloidogyne incognita

Under two monoxenic culture techniques of growing plants (filter paper and silica sand cultures), sugar in root exudate from Meloidogyne incognita-infected tomato increased 133 to 836% over controls. In contrast, amino acids were moderately reduced 52 to 56%. Chromatographic analysis showed that galled root exudate contained three sugars, twelve amino acids, and three organic acids, whereas healthy root exudate contained four sugars, fifteen amino acids, and four organic acids. Polysaccharide was responsible for the large increase of sugars in galled root exudates. The concn and the absolute amount of total sugars in the infected plant xylem sap were greater than in healthy plant xylem sap up to 6 wk after inoculation, whereas amino acids were moderately lower than in controls throughout the test period. Chromatographic analysis showed that xylem sap from both healthy and infected plants at 4 wk after inoculation contained four sugars and five organic acids. We identified 18 and 17 amino acids in the healthy and infected plant xylem sap, respectively. The concn of sugar increased as the nematode inoculum increased at 2, 4 and 6 wk after inoculation. The amino acids in all samples from the infected plant moderately decreased with an increase of nematode inoculum. We suggest that changes in total sugars and amino acids, of infected plant xylem sap and root exudate are a probable mechanism by which tomato plants are predisposed to Fusarium wilt.     

Cereal root exudates contain highly structurally complex polysaccharides with soil‐binding properties

Rhizosheaths function in plant?soil interactions, and are proposed to form due to a mix of soil particle entanglement in root hairs and the action of adhesive root exudates. The soil‐binding factors released into rhizospheres to form rhizosheaths have not been characterised. Analysis of the high‐molecular‐weight (HMW) root exudates of both wheat and maize plants indicate the presence of complex, highly branched polysaccharide components with a wide range of galactosyl, glucosyl and mannosyl linkages that do not directly reflect cereal root cell wall polysaccharide structures. Periodate oxidation indicates that it is the carbohydrate components of the HMW exudates that have soil‐binding properties. The root exudates contain xyloglucan (LM25), heteroxylan (LM11/LM27) and arabinogalactan‐protein (LM2) epitopes, and sandwich‐ELISA evidence indicates that, in wheat particularly, these can be interlinked in multi‐polysaccharide complexes. Using wheat as a model, exudate‐binding monoclonal antibodies have enabled the tracking of polysaccharide release along root axes of young seedlings, and their presence at root hair surfaces and in rhizosheaths. The observations indicate that specific root exudate polysaccharides, distinct from cell wall polysaccharides, are adhesive factors secreted by root axes, and that they contribute to the formation and stabilisation of cereal rhizosheaths.     

Mechanisms of microbially enhanced Fe acquisition in red clover (Trifolium pratense L.)

Soil microorganisms may play an important role in plant Fe uptake from soils with low Fe bioavailability, but there is little direct experimental evidence to date. We grew red clover, an Fe-efficient leguminous plant, in a calcareous soil to investigate the role of soil microbial activity in plant Fe uptake. Compared with plants grown in non-sterlie (NS) grown plants, growth and Fe content of the sterile(s) grown plants was significantly inhibited, but was improved by foliar application of Fe EDTA, indicating that soil microbial activity should play an important role in plant Fe acquisition. When soil solution was incubated with phenolic root exudates from Fe-deficient red clover, a few microbial species thrived while growth of the rest was inhibited, suggesting that the Fe-deficient (-Fe) root exudates selectively influenced the rhizosphere's microbial community. Eighty six per cent of the phenolic-tolerant microbes could produce siderophore [the Fe(III) chelator] under -Fe conditions, and 71% could secrete auxin-like compounds. Interestingly, the synthetic and microbial auxins (MAs) significantly enhanced the Ferric reduction system, suggesting that MAs, in addition to siderophores, are important to plant Fe uptake. Finally, plant growth and Fe uptake in sterilized soil were significantly increased by rhizobia inoculation. Root Fe-EDTA reductase activity in the -Fe plant was significantly enhanced by rhizobia infection, and the rhizobia could produce auxin but not siderophore under Fe-limiting conditions, suggesting that the contribution of nodulating rhizobia to plant Fe uptake can be at least partially attributed to stimulation of turbo reductase activity through nodule formation and auxin production in the rhizosphere. Based on these observations, we propose as a model that root exudates from -Fe plants selectively influence the rhizosphere microbial community, and the microbes in turn favour plant Fe acquisition by producing siderophores and auxins.     

Stimulated saprotrophic fungi in arable soil extend their activity to the rhizosphere and root microbiomes of crop seedlings

Saprotrophic fungi play an important role in ecosystem functioning and plant performance, but their abundance in intensively managed arable soils is low. Saprotrophic fungal biomass in arable soils can be enhanced with amendments of cellulose-rich materials. Here, we examined if sawdust-stimulated saprotrophic fungi extend their activity to the rhizosphere of crop seedlings and influence the composition and activity of other rhizosphere and root inhabitants. After growing carrot seedlings in sawdust-amended arable soil, we determined fungal and bacterial biomass and community structure in roots, rhizosphere and soil. Utilization of root exudates was assessed by stable isotope probing (SIP) following ¹³CO₂-pulse-labelling of seedlings. This was combined with analysis of lipid fatty acids (PLFA/NLFA-SIP) and nucleic acids (DNA-SIP). Sawdust-stimulated Sordariomycetes colonized the seedling's rhizosphere and roots and actively consumed root exudates. This did not reduce the abundance and activity of bacteria, yet higher proportions of α-Proteobacteria and Bacteroidia were seen. Biomass and activity of mycorrhizal fungi increased with sawdust amendments, whereas exudate consumption and root colonization by functional groups containing plant pathogens did not change. Sawdust amendment of arable soil enhanced abundance and exudate-consuming activity of saprotrophic fungi in the rhizosphere of crop seedlings and promoted potential beneficial microbial groups in root-associated microbiomes.     

Iron plaque decreases cadmium accumulation in Oryza sativa L. and serves as a source of iron

• Cadmium (Cd) contamination occurs in paddy soils; hence it is necessary to reduce Cd content of rice. Application and mode of action of ferrous sulphate in minimizing Cd in rice was monitored in the present study.
• Pot culture with Indian rice variety Swarna (MTU 7029) was maintained in Cd‐spiked soil containing ferrous sulphates, which is expected to reduce Cd accumulation in rice. Responses in rhizosphere pH, root surface, metal accumulation in plant and molecular physiological processes were monitored.
• Iron plaque was induced on root surfaces after FeSO4 application and the amount of Fe in plaque reduced with increases in Cd in the soil. Rhizosphere pH decreased during plaque formation and became more acidic due to secretion of organic acids from the roots under Cd treatment. Moreover, iron chelate reductase activity increased with Cd treatment, but in the absence of Cd, activity of this enzyme increased in plaque‐induced plants. Cd treatment caused expression of OsYSL18, whereas OsYSL15 was expressed only in roots without iron plaque. Fe content of plants increased during plaque formation, which protected plants from Cd‐induced Fe deficiency and metal toxicity. This was corroborated with increased biomass, chlorophyll content and quantum efficiency of photo‐synthesis among plaque‐induced plants.
• We conclude that ferrous sulphate‐induced iron plaque prevents Cd accumulation and Fe deficiency in rice. Iron released from plaque via organic acid mediated dissolution during Cd stress.

     

Flagella-driven chemotaxis towards exudate components is an important trait for tomato root colonization by Pseudomonas fluorescens

Motility is a major trait for competitive tomato root-tip colonization by Pseudomonas fluorescens. To test the hypothesis that this role of motility is based on chemotaxis toward exudate components, cheA mutants that were defective in flagella-driven chemotaxis but retained motility were constructed in four P. fluorescens strains. After inoculation of seedlings with a 1:1 mixture of wild-type and nonmotile mutants all mutants had a strongly reduced competitive root colonizing ability after 7 days of plant growth, both in a gnotobiotic sand system as well as in nonsterile potting soil. The differences were significant on all root parts and increased from root base to root tip. Significant differences at the root tip could already be detected after 2 to 3 days. These experiments show that chemotaxis is an important competitive colonization trait. The best competitive root-tip colonizer, strain WCS365, was tested for chemotaxis toward tomato root exudate and its major identified components. A chemotactic response was detected toward root exudate, some organic acids, and some amino acids from this exudate but not toward its sugars. Comparison of the minimal concentrations required for a chemotactic response with concentrations estimated for exudates suggested that malic acid and citric acid are among major chemo-attractants for P. fluorescens WCS365 cells in the tomato rhizosphere.     

Mobilization of iron and other micronutrient cations from a calcareous soil by plant-borne,microbial, and synthetic metal chelators

Mobilization of Fe, Zn, Cu, and Mn by various chelators from a calcareous soil was measured using a simple dialysis tube/complexing resin system. Root exudates from Fe-deficient barley increased the concentrations of all four metals in solution by, on average, a factor of 20, and the addition of complexing resin as a sink for heavy metal cations forced steady state solution concentrations to be reached sooner. Root exudates mobilized increasing amounts of the various micronutrients in the following order: Cu<Fe<Zn<Mn. Phytosiderophores isolated from root exudates of Fe-deficient barley mobilized similar amounts of Cu and Zn but somewhat more Fe and considerably more Mn than crude exudate. The synthetic chelators EDDHA and DTPA showed low specificity in micronutrient mobilization, but the microbial siderophore Desferal was relatively more specific, preferentially mobilizing Fe and Mn. The data indicates that phytosiderophores are capable of increasing the amount of complexed cations in solution. Despite their lack of specificity, phytosiderophores were just as effective as Desferal increasing the availability of Fe. Thus, phytosiderophores, as plant-borne chelators, are certainly of significance for the Fe nutrition of cereals grown in calcareous soils.     

Characterization of the high affinity Zn transporter from Noccaea caerulescens, NcZNT1, and dissection of its promoter for its role in Zn uptake and hyperaccumulation

? In this paper, we conducted a detailed analysis of the ZIP family transporter, NcZNT1, in the zinc (Zn)/cadmium (Cd) hyperaccumulating plant species, Noccaea caerulescens, formerly known as Thlaspi caerulescens. NcZNT1 was previously suggested to be the primary root Zn/Cd uptake transporter. Both a characterization of NcZNT1 transport function in planta and in heterologous systems, and an analysis of NcZNT1 gene expression and NcZNT1 protein localization were carried out. ? We show that NcZNT1 is not only expressed in the root epidermis, but also is highly expressed in the root and shoot vasculature, suggesting a role in long-distance metal transport. Also, NcZNT1 was found to be a plasma membrane transporter that mediates Zn but not Cd, iron (Fe), manganese (Mn) or copper (Cu) uptake into plant cells. ? Two novel regions of the NcZNT1 promoter were identified which may be involved in both the hyperexpression of NcZNT1 and its ability to be regulated by plant Zn status. ? In conclusion, we demonstrate here that NcZNT1 plays a role in Zn and not Cd uptake from the soil, and based on its strong expression in the root and shoot vasculature, could be involved in long-distance transport of Zn from the root to the shoot via the xylem.