Apical Region Of Root Research Articles

Evaluation of hard tissue characteristics and calcifications in pulp tissue of hypomineralized permanent molars using micro-computed tomography

ObjectivesTo determine and compare pulp volume, dentin mineral density, presence of microcracks, pulp stones, and accessory canals, as well as their localizations in root regions for hypomineralized and healthy teeth. DesignThis study included 60 extracted permanent molar teeth, categorized into hypomineralized and healthy groups (n = 30 each). The hypomineralized group comprised molar teeth with limited white, yellow, or brown opacities, post-eruptive breakdown, or extensive restoration or crown damage. The healthy group included caries-free molar teeth without these characteristics. Using 3D micro-computed tomography images pulp volume, dentin mineral density, and the presence and locations of microcracks, pulp stones, and accessory canals were determined for each group. Statistical analyses were conducted using Independent T-test and Chi-square test, with significance set at p < 0.05. ResultsThere was no statistically significant difference between the groups regarding pulp volume and microcracks (p ≥ 0.05). The number of accessory canals was significantly greater in the cervical (p = 0.011; p < 0.05) and middle (p = 0.010; p < 0.05) regions of the hypomineralized teeth than healthy teeth. Dentin mineral density was statistically higher in the apical, middle, and cervical root regions (p < 0.001; p < 0.05); however, the number of pulp stones was found to be greater in the cervical regions of healthy teeth compared with those with hypomineralization (p = 0.026; p < 0.05). ConclusionThere were lower dentin mineral density measurements, a decreased number of pulp stones in the cervical region, and a greater number of accessory canals in the middle and cervical regions of hypomineralized teeth compared with healthy teeth.

Measurement of Anterior Maxillary Alveolar Ridge Dimension and Assessment of Sagittal Root Position by Cone Beam Computerized Tomography (CBCT)

Maxillary anterior region is the implant site that may require the most rigorous pre-operative assessment as it will have a direct influence on aesthetic outcome and stability of the dental implant. In the present study, CBCT (cone beam computerized tomography) images were used to evaluate alveolar ridge dimension in the maxillary anterior region. This observational radiographic study was done at Nepal Medical College Teaching Hospital. The width of the alveolar bone was measured from the labial cortex to the palatal cortex of the maxillary anterior teeth in mm at the alveolar crest (L1), mid-root (L2), and apical root region (L3) for each tooth. Alveolar height was also measured from the alveolar crest to the floor of the nasal fossa. The Sagittal Root Position (SRP) of the maxillary anterior teeth was also assessed. Results showed that the maximum width of the alveolar bone was seen at L3 of canine and lateral incisor showed least width of alveolar bone width at L1. Maximum alveolar bone height was seen in canines. Males were seen to have increased width of the alveolar bone as compared to the females in all anterior teeth. The most frequent sagittal root position was class I which was seen in 270 (51.4%) of the total teeth examined, which was followed by class IV observed in 210 (40%) of the teeth examined. It could be concluded that for maxillary anterior region, additional regeneration therapy maybe required since class I is the most frequent SRP observed.

Effects of ethylenediaminetetraacetic acid, citric acid, and etidronic acid on root dentin mineral content and bond strength of a bioceramic-based sealer: A scanning electron microscopy-energy dispersive spectroscopy study.

This study assessed the impact of chelating agents, 17% ethylenediaminetetraacetic acid (EDTA), 10% citric acid (CA), and 18% etidronic acid (HEDP), on root dentin mineral content. Scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) was applied to analyze changes, and the push-out bond strength test was used to measure dentin adhesion of Well-Root ST, a bioceramic root canal sealer. A total of 80 extracted single-rooted lower premolar teeth were included in this study and randomly divided into four groups (n=20): group 1 (17% EDTA), group 2 (10% CA), group 3 (18% HEDP), and group 4 (distilled water, control). After irrigation and drying, SEM-EDS was applied to analyze eight samples from each group at coronal, middle, and apical root regions for mineral content and SEM images. The remaining 12 samples underwent a push-out bond strength test using Well-Root ST sealer and gutta-percha. Kruskal-Wallis and Dunn's tests were used for statistical analyses. Statistically significant differences were found between groups (P<0.05). SEM-EDS showed significant differences in C, O, Ca, P, and Ca/P content, with no significant differences in Na and Mg. Push-out bond strength was significantly higher in the 17% EDTA, 10% CA, and 18% HEDP groups compared to the control group, with no significant differences between chelating agents. Chelating agents altered root dentin mineral content and improved the adhesive properties of the bioceramic sealer. These findings highlight the importance of considering the selection and use of chelating agents in the clinical practice for root canal treatment.

The osteoclastic activity in apical distal region of molar mesial roots affects orthodontic tooth movement and root resorption in rats

The utilization of optimal orthodontic force is crucial to prevent undesirable side effects and ensure efficient tooth movement during orthodontic treatment. However, the sensitivity of existing detection techniques is not sufficient, and the criteria for evaluating optimal force have not been yet established. Here, by employing 3D finite element analysis methodology, we found that the apical distal region (A-D region) of mesial roots is particularly sensitive to orthodontic force in rats. Tartrate-resistant acidic phosphatase (TRAP)-positive osteoclasts began accumulating in the A-D region under the force of 40 grams (g), leading to alveolar bone resorption and tooth movement. When the force reached 80 g, TRAP-positive osteoclasts started appearing on the root surface in the A-D region. Additionally, micro-computed tomography revealed a significant root resorption at 80 g. Notably, the A-D region was identified as a major contributor to whole root resorption. It was determined that 40 g is the minimum effective force for tooth movement with minimal side effects according to the analysis of tooth movement, inclination, and hyalinization. These findings suggest that the A-D region with its changes on the root surface is an important consideration and sensitive indicator when evaluating orthodontic forces for a rat model. Collectively, our investigations into this region would aid in offering valuable implications for preventing and minimizing root resorption during patients’ orthodontic treatment.

The effect of periapical bone defects on stress distribution in teeth with periapical periodontitis: a finite element analysis

BackgroundApical periodontitis directly affects the stress state of the affected tooth owing to the destruction of the periapical bone. Understanding the mechanical of periapical bone defects/tooth is clinically meaningful. In this study, we evaluate the effect of periapical bone defects on the stress distribution in teeth with periapical periodontitis using finite element analysis.MethodsFinite element models of normal mandibular second premolars and those with periapical bone defects (spherical defects with diameters of 5, 10, 15, and 20 mm) were created using a digital model design software. The edges of the mandible were fixed and the masticatory cycle was simplified as oblique loading (a 400 N force loaded obliquely at 45° to the long axis of the tooth body) to simulate the tooth stress state in occlusion and analyze the von Mises stress distribution and tooth displacement distribution in each model.ResultsOverall analysis of the models: Compared to that in the normal model, the maximum von Mises stresses in all the different periapical bone defect size models were slightly lower. In contrast, the maximum tooth displacement in the periapical bone defect model increased as the size of the periapical bone defect increased (2.11–120.1% of increase). Internal analysis of tooth: As the size of the periapical bone defect increased, the maximum von Mises stress in the coronal cervix of the tooth gradually increased (2.23–37.22% of increase). while the von Mises stress in the root apical region of the tooth showed a decreasing trend (41.48–99.70% of decrease). The maximum tooth displacement in all parts of the tooth showed an increasing trend as the size of the periapical bone defect increased.ConclusionsThe presence of periapical bone defects was found to significantly affect the biomechanical response of the tooth, the effects of which became more pronounced as the size of the bone defect increased.

Evaluation of Bond Strength and Fracture Load of Teeth With Flared Root Canals Restored With Prefabricated, Anatomical, and Computer-aided Design and Computer-aided Manufacturing Fiber Posts.

This study compared the use of anatomical glass fiber posts using bulk-fill composite resin with computer-aided design and computer-aided manufacturing (CAD/CAM) milled glass fiber post in oversized root canals, through bond strength (BS) and fracture resistance (FR) tests (fracture load). A total of 48 mandibular premolars were selected, half of them had their crowns removed at the cemento-enamel junction (CEJ) and the other half were sectioned 2 mm above the CEJ. Subsequently, teeth were endodontically treated. After 1 week, the standard preparation of the canals was carried out, and the roots were divided into three groups (n=16), according to the use of different restorative techniques (control: prefabricated glass fiber post [PFP], direct anatomical glass fiber post [AFP], and CAD/CAM milled glass fiber post [MFP]). After luting procedures using Single Bond Universal and RelyX Ultimate (3M ESPE), for eight teeth in each group, six specimens were obtained (two slices from each root third: cervical, middle, and apical). For the remaining eight roots of each group, standardized preparations for metal-free crowns, milling of 5 mol% yttria-stabilized tetragonal zirconia polycrystalline, cementation of the crowns, and periodontal ligament simulation were performed. Then, for each group, the BS was evaluated through the push-out test, and the FR was evaluated in compression. The data obtained from BS were submitted to two-way analysis of variance (ANOVA; group vs root region) and Tukey (α=0.05) and from FR to one-way ANOVA (group) and Tukey (α=0.05). For the BS test, the MFP group was statistically superior to the PFP group in all root regions and was statistically superior to the AFP group only in the cervical region, being statistically similar in the middle and apical root regions. For the FR test, the MFP group was statistically superior to the PFP and AFP groups. The milled fiber post technique can be a legitimate alternative in the restoration of weakened roots with flared root canals.

Minimally Invasive Approaches in Endodontic Practice by Gianluca Plotino, Editor. Cham, Switzerland: Sringer Nature; 2021

A new must-read textbook, Minimally Invasive Approaches in Endodontic Practice, is designed by top experts for the future generation of specialists in endodontics. The textbook consists of 9 beautifully-written Chapters carefully prepared by 18 co-authors from 11 countries (Brazil, Canada, France, Greece, Hong Kong [the Special Administrative Region, China], Italy, Norway, Portugal, Spain, United States of America, and Venezuela) under the leadership of Gianluca Plotino (Italy). For the practitioners who are only starting to grow or already deeply specialize in endodontic microsurgery, the Chapter 7, “Minimally Invasive Approach to Endodontic Retreatment and Surgical Endodontics” by Mario Zuolo (São Paulo, Brazil) and Leandro Pereira (Campinas, Brazil) is the useful one. The chapter highlights important data in a very informative academic way. The table 7.1 is more than worth of attention due to the state of the art comparison of technical differences between macro- and microsurgery. The apical microsurgery success rate of around 90 percent comparing to less than 60 percent of macrosurgery clearly shows the advantages of the first one. Perfect illustration of retrocavity filing (i.e., retrofilling) is a role model part of protocol of the microsurgical management for the apical root region. In summary, this textbook is a very important source of knowledge and practical skills for every dental practitioner related more or less with the endodontics.

Oral stem cells, decoding and mapping the resident cells populations.

ABSTRACTThe teeth and their supporting tissues provide an easily accessible source of oral stem cells. These different stem cell populations have been extensively studied for their properties, such as high plasticity and clonogenicity, expressing stem cell markers and potency for multilineage differentiation in vitro. Such cells with stem cell properties have been derived and characterised from the dental pulp tissue, the apical papilla region of roots in development, as well as the supporting tissue of periodontal ligament that anchors the tooth within the alveolar socket and the soft gingival tissue. Studying the dental pulp stem cell populations in a continuously growing mouse incisor model, as a traceable in vivo model, enables the researchers to study the properties, origin and behaviour of mesenchymal stem cells. On the other side, the oral mucosa with its remarkable scarless wound healing phenotype, offers a model to study a well-coordinated system of healing because of coordinated actions between epithelial, mesenchymal and immune cells populations. Although described as homogeneous cell populations following their in vitro expansion, the increasing application of approaches that allow tracing of individual cells over time, along with single-cell RNA-sequencing, reveal that different oral stem cells are indeed diverse populations and there is a highly organised map of cell populations according to their location in resident tissues, elucidating diverse stem cell niches within the oral tissues. This review covers the current knowledge of diverse oral stem cells, focusing on the new approaches in studying these cells. These approaches “decode” and “map” the resident cells populations of diverse oral tissues and contribute to a better understanding of the “stem cells niche architecture and interactions. Considering the high accessibility and simplicity in obtaining these diverse stem cells, the new findings offer potential in development of translational tissue engineering approaches and innovative therapeutic solutions.

Short-chain aldehydes increase aluminum retention and sensitivity by enhancing cell wall polysaccharide contents and pectin demethylation in wheat seedlings

Upon environmental stimuli, aldehydes are generated downstream of reactive oxygen species and thereby contribute to severe cell damage. In this study, using two wheat genotypes differing in aluminum (Al) tolerance, we investigated the effects of lipid peroxidation-derived aldehydes on cell wall composition and subsequent Al-binding capacities. The spatial accumulation of Al along wheat roots was found to the generation of reactive aldehydes, which are highly localized to the apical regions of roots. Elimination of aldehydes by carnosine significantly reduced Al contents in root tips, with a concomitant alleviation of root growth inhibition. In contrast, root growth and Al accumulation were exacerbated by application of the short-chain aldehyde (E)−2-hexenal. We further confirmed that cell wall binding capacity, rather than malate efflux or pH alteration strategies, is associated with the aldehyde-induced accumulation of Al. Scavenging of lipid-derived aldehydes reduced Al accumulation in the pectin and hemicellulose 1 (HC1) fractions of root cell walls, whereas exposure to (E)−2-hexenal promoted a further accumulation of Al, particularly in the cell wall HC1 fraction of the Al-sensitive genotype. Different strategies were introduced by pectin and HC1 to accumulate Al in response to aldehydes in wheat roots. Accumulation in pectin is based on a reduction of methylation levels in response to elevated pectin methylesterase activity and gene expression, whereas that in HC1 is associated with an increase in polysaccharide contents. These findings indicate that aldehydes exacerbate Al phytotoxicity by enhancing Al retention in cell wall polysaccharides.

Expression analysis of plant intracellular Ras-group related leucine-rich repeat proteins (PIRLs) in Arabidopsis thaliana

Arabidopsis thaliana contains a family of nine genes known as plant intracellular Ras-group related leucine-rich repeat (LRR) proteins (PIRLs). These are structurally similar to animals and fungal LRR proteins and play important roles in developmental pathways. However, to date, no detailed tissue-specific expression analysis of these PIRLs has been performed. Therefore, in this study, we generated promoter:GUS transgenic plants for the nine A. thaliana PIRL genes and identified their expression patterns in seedlings and floral organs at different developmental stages. Most PIRL members showed expression in the root apical region and in the vascular tissue of primary and lateral roots. Shoot apex-specific expression was recorded for PIRL1 and PIRL8. Furthermore, PIRL1, PIRL3, PIRL5, PIRL6, and PIRL7 showed distinct expression patterns in flowers, especially in pollen and anthers. In addition, co-expression network analysis identified cases where PIRLs were co-expressed with other genes known to have specific functions related to growth and development. Taken together, the tissue-specific expression patterns of PIRL genes improve our understanding of the functions of this gene family in plant growth and development.

Monitoring the apical growth characteristics of hairy roots using non-invasive laser speckle contrast imaging.

Hairy roots are used to produce plant agents and additives. Due to their heterogeneous structure and growth characteristics, it is difficult to determine growth‐related parameters continuously and in real time. Laser speckle contrast analysis is widely used as a non‐destructive measurement technique in material testing or in medical technology. This type of analysis is based on the principle that moving objects or particles cause fluctuations in stochastic interference patterns known as speckle patterns. They are formed by the random backscattering of coherent laser light on an optically rough surface. A Laser Speckle Imager, which is well established for speckle studies of hemodynamics, was used for the first time for non‐invasive speckle measurements on hairy roots to study dynamic behavior in plant tissue. Based on speckle contrast, a specific flux value was defined to map the dynamic changes in the investigated tissue. Using this method, we were able to predict the formation of lateral strands and to identify the growth zone in the apical root region, as well as dividing it into functional regions. This makes it possible to monitor physiological processes in the apical growth zone in vivo and in real time without labeling the target structures.

Exploration of Candidate Genes Derived from SNPs Associated with Phenotypic Root Plasticity Using Philippine Rice Germplasm for Drought Adaptation

Phenotypic root plasticity is a crucial trait for stable growth, adaptability, and productivity under abiotic-stressed growing environments. However, the genetic determinants and mechanisms controlling the trait are largely unknown, thus limiting its breeding application. We previously found 17 single nucleotide polymorphism (SNPs) significantly associated with phenotypic root plasticity traits – particularly, total root length (TRL), total nodal root length (TNRL), and total lateral root length (TLRL) – under moderate and severe drought using selected Philippine rice germplasm by employing the genome-wide association studies (GWAS) approach. Here, we present around 92 candidate genes using these SNP data. The genes were derived from various functional categories and drought intensity dependent. These were further narrowed via Gene Ontology and gene expression profile at root apical regions using databases to those whose putative functions were likely to be associated with root development in response to drought stress. Sixteen (16) more interesting known or novel genes were selected and discussed. When these genes are validated, they can help improve rice adaptation to water-limited environments.

Guttaflow Bioseal as Monocone Obturation Technique: A Scanning Electron Microscopy Study

INTRODUCTION: This study compared the obturated surface area, the extrusion of root filling material beyond the apical foramen and the duration of obturation procedure in single-rooted mandibular premolar using monocone obturation technique. MATERIALS AND METHODS: The root canal of twenty single-rooted mandibular premolars were prepared, and then divided into two groups; Group 1 (GuttaFlow Bioseal (GFB) and a gutta-percha (GP) cone) and Group 2 (RoekoSeal Automix root canal sealer and a GP cone). The obturation procedure was timed and the obturation radiograph was taken after the procedure. The roots were sectioned perpendicularly and the surfaces were observed under scanning electron microscope. The images were transferred to the SketchAndCalc Area Calculator software for evaluation of the obturated surface area. RESULTS: The median score of obturated surface area in Group 1 and 2 at the apical was 86.51 and 83.00, at the middle was 90.48 and 87.35 and at the coronal was 93.00 and 83.39, respectively. The extrusion of root filling material between two groups did not show statistically significant difference. The mean duration of obturation in Group 1 and 2 was 149.50 and 137.60, respectively. CONCLUSIONS: The obturated surface area at the apical and middle root regions in Group 1 and 2 was comparable but at the coronal region, Group 1 showed 11.5% better coverage. The extrusion of root filling material in Group 1 and 2 was equivalent. Obturation procedure in Group 1 took 8.6% longer than in the Group 2.

SHORT-ROOT1 is critical to cell division and tracheary element development in rice roots.

The exocyst is a key factor in vesicle transport and is involved in cell secretion, cell growth, cell division and other cytological processes in eukaryotes. EXO70 is the key exocyst subunit. We obtained a gene, SHORT-ROOT1 (SR1), through map-based cloning and genetic complementation. SR1 is a conserved protein with an EXO70 domain in plants. SR1 mutation affected the whole root-development process: producing shorter radicles, adventitious roots and lateral roots, and demonstrating abnormal xylem development, resulting in dwarfing and reduced water potential and moisture content. SR1 was largely expressed in the roots, but only in developing root meristems and tracheary elements. The shortness of the sr1 mutant roots was caused by the presence of fewer meristem cells. The insitu histone H4 expression patterns confirmed that cell proliferation during root development was impaired. Tracheary element dysplasia was caused by marked decreases in the inner diameters of and distances between the perforations of adjacent tracheary elements. The membrane transport of sr1 mutants was blocked, affecting cell division in the root apical region and the development of root tracheary elements. The study of SR1 will deepen our understanding of the function of EXO70 genes in Oryza sativa (rice) and guide future studies on the molecular mechanisms involved in plant root development.

A Rare Case of Radicular Dens Invaginatus (Dens in Dente) in a Dog

A rare case of radicular dens invaginatus (dens in dente) was found during dental cleaning of a 5-year-old male Rottweiler dog. Radiographic examination revealed intense radiopacity, which extended from the crown to the apical root region of the affected tooth. Macroscopically, the crown of the left maxillary first molar tooth (209) had irregular and deformed buccal and lingual surfaces. Microscopic examination revealed dentine invagination in the pulp cavity in of the crown and root and pulp necrosis. Based on the gross, radiographic and histological findings, a diagnosis of radicular dens invaginatus was made.

Dynamics of radial oxygen loss in mangroves subjected to waterlogging.

Tidal flooding can directly result in oxygen (O2) shortage, however the functions of root aeration in flooding tolerance and O2 dynamics within mangroves are still poorly understood. Thus, in this study, the correlations among waterlogging tolerance, root porosity and O2 movement within the plants were investigated using two mangrove species (Aegiceras corniculatum and Bruguiera gymnorrhiza) and a semi-mangrove Heritiera littoralis. Based on the present data, the species A. corniculatum and B. gymnorrhiza, which possessed higher root porosity, exhibited higher waterlogging tolerance, while H. littoralis is intolerant. Increased root porosity, leaf stoma, and total ROL were observed in the roots of A. corniculatum and B. gymnorrhiza growing in stagnant solution when compared to respective aerated controls. As for ROL spatial pattern along roots, external anaerobic condition could promote ROL from apical root regions but reduce ROL from basal roots, leading to a 'tighter barrier'. In summary, the present study indicated that the plants (e.g., A. corniculatum and B. gymnorrhiza) prioritized to ensure O2 diffusion towards root tips under waterlogging by increasing aerenchyma formation and reducing O2 leakage at basal root regions.

Modulation of the defence responses against Cd in willow species through a multifaceted analysis

Willow, due to the extensive root system, high transpiration rates and ability to accumulate large amounts of cadmium, is considered particularly useful for green remediation practices. In this study two different willow species, Salix viminalis and Salix alba, were used to assess possible differences in their ability of cadmium accumulation and to analyse in detail the physiology of their response to treatments with this metal using a multidisciplinary approach. Plants were grown in hydroponics and treated with 0, 50 and 100 μM Cd2+ (CdCl2) for 7 and 14 days. Cadmium content, oxidative stress, both evaluated by biochemical and histochemical techniques, antioxidant response, leaf stomatal conductance and photosynthetic efficiency were measured in control and treated roots and/or leaves. The two willow species removed cadmium with a high efficiency from the growth solution; however, the highest contents of Cd recorded in plants grown in the presence of the lower Cd concentrations suggest a limited capacity of metal accumulation. No photochemical limitation characterised treated plants, probably due to the ability to store large amounts of Cd in the root compartment, with reduction of damage to the photosynthetic machinery. S. viminalis, able to uptake cadmium also in the root apical region, seemed to be a more efficient accumulator than S. alba and, thanks to a relatively higher antioxidant response, did not show a higher level of oxidative stress. On the basis of the above, the two plant species, in particular S. viminalis, are confirmed as useful for cadmium phytostabilisation/phytoextraction.

Maxillary molar root protrusion into the maxillary sinus: a comparison of cone beam computed tomography and panoramic findings

This study aimed to examine the prevalence of molar roots protruding into the maxillary sinus and to determine the panoramic radiographic signs as correlated with cone beam computed tomography (CBCT). CBCT images of 354 roots were assessed and classified into three types, according to the relationship between the root and maxillary sinus. The prevalence of root protrusion into the maxillary sinus was calculated then the panoramic images assessed. After excluding some unidentified roots on the panoramic images, 200 were investigated for panoramic signs, including (i) projection of the root apex into the sinus cavity, (ii) interruption of the maxillary sinus floor’s cortex, (iii) absence of periodontal ligament space, (iv) darkening of the involved root region, and (v) upward curving of the sinus floor. The respective correlation between the panoramic signs and CBCT types was assessed. Forty-six percent of roots showed protrusion into the sinus with the palatal root of the first molar having the greatest prevalence (33/200 roots). The panoramic signs ‘projection of the root apex in the sinus cavity’ and ‘darkening of the involved root apical region’ both strongly indicated root protrusion into the maxillary sinus (P<0.05).

Velamen or uniseriate epidermis? Root apices in Bromeliaceae Juss

The anatomy of Bromeliaceae roots has attracted the attention of researchers for a long time. Several authors have described them by highlighting characters associated with mechanisms of water uptake, water retention and adaptation to the environment. In this context, the dermal tissue is frequently mentioned, being described by different authors as uniseriate or pluriestratified epidermis, or even as velamen. In the present study we analyzed the apical meristem region of adventitious roots of nine species belonging to the Pitcairnioideae, Bromelioideae and Tillandsioideae subfamilies. The goal of this study was to elucidate the ontogenetic origin of the tissue referred by several authors as velamen. The root anatomy of analyzed species showed characteristics shared by all taxa, such as the presence of uniseriate epidermis, parenchymal cortex, idioblasts and air channels, as well as a polyarch vascular cylinder. The ontogenetic analysis of the root epidermis carried out in this study enabled us to clarify issues related to the anatomy of this organ that were previously unknown. Our analysis revealed the presence of a uniseriate epidermis in all analyzed taxa in this study, thus increasing the knowledge about the root anatomy of the family.

Contribution of NtZIP1-Like to the Regulation of Zn Homeostasis.

Tobacco has frequently been suggested as a candidate plant species for use in phytoremediation of metal contaminated soil but knowledge on the regulation of its metal-homeostasis is still in the infancy. To identify new tobacco metal transport genes that are involved in Zn homeostasis a bioinformatics study using the tobacco genome information together with expression analysis was performed. Ten new tobacco metal transport genes from the ZIP, NRAMP, MTP, and MRP/ABCC families were identified with expression levels in leaves that were modified by exposure to Zn excess. Following exposure to high Zn there was upregulation of NtZIP11-like, NtNRAMP3, three isoforms of NtMTP2, three MRP/ABCC genes (NtMRP5-like, NtMRP10-like, and NtMRP14 like) and downregulation of NtZIP1-like and NtZIP4. This suggests their involvement in several processes governing the response to Zn-related stress and in the efficiency of Zn accumulation (uptake, sequestration, and redistribution). Further detailed analysis of NtZIP1-like provided evidence that it is localized at the plasma membrane and is involved in Zn but not Fe and Cd transport. NtZIP1-like is expressed in the roots and shoots, and is regulated developmentally and in a tissue-specific manner. It is highly upregulated by Zn deficiency in the leaves and the root basal region but not in the root apical zone (region of maturation and absorption containing root hairs). Thus NtZIP1-like is unlikely to be responsible for Zn uptake by the root apical region but rather in the uptake by root cells within the already mature basal zone. It is downregulated by Zn excess suggesting it is involved in a mechanism to protect the root and leaf cells from accumulating excess Zn.