Region Of Root Apex Research Articles

Analysis of Pulpal Stress in Varied Orthodontic Tooth Movements at Different Bone Levels: A Finite Element Analysis

Aim To analyze the pulpal stress in varied orthodontic tooth movements at ideal force levels and different bone levels, and compare any differences in pulpal stress values between anterior and posterior teeth. Materials and Methods Four Finite Element Method models of incisor and molar teeth were simulated with normal bone height and 50% bone height. Each of these models was loaded with five different types of orthodontic tooth movements—Tipping, Translation, Intrusion, Extrusion, and Rotation. The ideal force levels simulated for each type of tooth movement were: Intrusion-20 g, Extrusion-60 g, Tipping-60 g, Translation-120 g, Rotation-60 g. The pulpal stress was evaluated at three levels—pulp chamber, pulp canal, and below root apex, so that we get three values of pulpal stress for anterior and posterior teeth, for each type of tooth movement and its corresponding force level. Results The results showed that in both incisor and molar models with normal bone height as well as 50% bone height, rotation gave the highest pulpal stress while translation gave the least. In both incisor and molar models with normal bone height as well as 50% bone height, pulpal stress was found out to be highest in the root apex region of the tooth. The stress values for incisor and molar models with 50% bone height were found to be almost double that of the models with normal bone height. The pulpal stress for incisor teeth was found to be greater than the molar teeth for all types of tooth movement. Conclusion The present findings indicate that the stress manifested below the root apex is highest. Rotational movements induce the highest stress and translational forces develop the lowest stress related to the physiologic capillary blood pressure. Furthermore, in situations with reduced periodontium, lower forces are needed to reach the maximum tolerable stress compared with teeth with intact periodontium.

Role of chondroitin sulfate in the developmental and healing process of the dental pulp in mice.

Chondroitin sulfate proteoglycan (CSPG), one of the major extracellular matrices, plays an important part in organogenesis. Its core protein and chondroitin sulfate (CS) chain have a specific biological function. To elucidate the role of CS in the developmental and healing process of the dental pulp, we performed an experimental tooth replantation in CS N-acethylgalactosaminyltransferase-1 (T1) gene knockout (KO) mice. We also performed cell proliferation assay and qRT-PCR analysis for the WT and T1KO primary dental pulp cells using T1-siRNA technique and external CS. During tooth development, CS was diffusely expressed in the dental papilla, and with dental pulp maturation, CS disappeared from the differentiated areas, including the odontoblasts. In fully developed molars, CS was restricted to the root apex region colocalizing with Gli1-positive cells. In the healing process after tooth replantation, CD31-positive cells accumulated in the CS-positive stroma in WT molars. In T1KO molars, the appearance of Ki67- and Gli1-positive cells in the dental pulp was significantly fewer than in WT molars in the early healing stage, and collagen I-positive reparative dentin formation was not obvious in T1KO mice. In primary culture experiments, siRNA knockdown of T1 gene significantly suppressed cell proliferation in WT dental pulp cells, and the mRNA expression of cyclin D1 and CD31 was significantly upregulated by external CS in T1KO dental pulp cells. These results suggest that CS is involved in the cell proliferation and functional differentiation of dental pulp constituent cells, including vascular cells, in the healing process of dental pulp tissue after tooth injury.

Potential involvement of drought-induced Ran GTPase CLRan1 in root growth enhancement in a xerophyte wild watermelon

Enhanced root growth is known as the survival strategy of plants under drought. Previous proteome analysis in drought-resistant wild watermelon has shown that Ran GTPase, an essential regulator of cell division and proliferation, was induced in the roots under drought. In this study, two cDNAs were isolated from wild watermelon, CLRan1 and CLRan2, which showed a high degree of structural similarity with those of other plant Ran GTPases. Quantitative RT-PCR and promoter-GUS assays suggested that CLRan1 was expressed mainly in the root apex and lateral root primordia, whereas CLRan2 was more broadly expressed in other part of the roots. Immunoblotting analysis confirmed that the abundance of CLRan proteins was elevated in the root apex region under drought stress. Transgenic Arabidopsis overexpressing CLRan1 showed enhanced primary root growth, and the growth was maintained under osmotic stress, indicating that CLRan1 functions as a positive factor for maintaining root growth under stress conditions.

Root cap-dependent gravitropic U-turn of maize root requires light-induced auxin biosynthesis via the YUC pathway in the root apex.

Gravitropism refers to the growth or movement of plants that is influenced by gravity. Roots exhibit positive gravitropism, and the root cap is thought to be the gravity-sensing site. In some plants, the root cap requires light irradiation for positive gravitropic responses. However, the mechanisms regulating this phenomenon are unknown. We herein report that maize roots exposed to white light continuously for ≥1-2h show increased indole-3-acetic acid (IAA) levels in the root tips, especially in the transition zone (1-3mm from the tip). Treatment with IAA biosynthesis inhibitors yucasin and l-kynurenine prevented any increases in IAA content and root curvature under light conditions. Analyses of the incorporation of a stable isotope label from tryptophan into IAA revealed that some of the IAA in roots was synthesized in the root apex. Furthermore, Zmvt2 and Zmyuc gene transcripts were detected in the root apex. One of the Zmyuc genes (ZM2G141383) was up-regulated by light irradiation in the 0-1mm tip region. Our findings suggest that IAA accumulation in the transition zone is due to light-induced activation of Zmyuc gene expression in the 0-1mm root apex region. Light-induced changes in IAA levels and distributions mediate the maize root gravitropic U-turn.

How and why do root apices sense light under the soil surface?

Light can penetrate several centimeters below the soil surface. Growth, development and behavior of plant roots are markedly affected by light despite their underground lifestyle. Early studies provided contrasting information on the spatial and temporal distribution of light-sensing cells in the apical region of root apex and discussed the physiological roles of plant hormones in root responses to light. Recent biological and microscopic advances have improved our understanding of the processes involved in the sensing and transduction of light signals, resulting in subsequent physiological and behavioral responses in growing root apices. Here, we review current knowledge of cellular distributions of photoreceptors and their signal transduction pathways in diverse root tissues and root apex zones. We are discussing also the roles of auxin transporters in roots exposed to light, as well as interactions of light signal perceptions with sensing of other environmental factors relevant to plant roots.

MeJA Affects Root Growth by Modulation of Transmembrane Auxin Flux in the Transition Zone

Biosynthesis and accumulation of jasmonate (JA) can regulate plant defense responses and organ development under insect herbivore stress conditions. One of these responses, the inhibition of root growth, is a common phenomenon. However, the physiological and molecular mechanisms of how JA affects root growth are not completely understood. In this study, the influence of MeJA treatment on auxin and proton flux rates in the root apex region of Col-0, coi1-1, pin2, and aux1-7 mutant lines was examined using a non-invasive micro-test technique. The auxin and H+ flux profiles taken from coi1-1 mutants suggest that the modulation of auxin and H+ flux by JA requires the function of COI1. The auxin and H+ flux in pin2 and aux1 mutants with and without JA treatment suggest that JA can affect polar auxin transport by regulating PIN-mediated auxin efflux and the AUX-mediated influx pathways. Furthermore, the expression levels of PIN1, PIN2, PIN3, PIN7, AUX1, and TIR1 genes were reduced under MeJA treatment, and expression levels of CYP79B2 and CYP79B3 were elevated. Together, these results suggest that JA signaling may modulate the auxin signaling pathways by regulating the expression of key genes.

Spatiotemporal dynamics of the electrical network activity in the root apex.

The study of electrical network systems, integrated with chemical signaling networks, is becoming a common trend in contemporary biology. Classical techniques are limited to the assessment of signals from doublets or triplets of cells at a fixed temporal bin width. At present, full characteristics of the electrical network distribution and dynamics in plant cells and tissues has not been established. Here, a 60-channels multielectrode array (MEA) is applied to study spatiotemporal characteristics of the electrical network activity of the root apex. Both intense spontaneous electrical activities and stimulation-elicited bursts of locally propagating electrical signals have been observed. Propagation of the spikes indicates the existence of excitable traveling waves in plants, similar to those observed in non-nerve electrogenic tissues of animals. Obtained data reveal synchronous electric activities of root cells emerging in a specific root apex region. The dynamic electrochemical activity of root apex cells is proposed to continuously integrate internal and external signaling for developmental adaptations in a changing environment.

Changes in cell-wall properties of wheat (Triticum aestivum) roots during aluminum-induced growth inhibition.

The effects of aluminum (Al) on root elongation, the mechanical extensibility of the cell wall, and the amount of cell-wall polysaccharides in the roots of Al-resistant (Atlas 66) and Al-sensitive (Scout 66) cultivars of wheat (Triticum aestivum L.) were examined. Exposure to 10 &mgr;M AlCl3 for 6 h inhibited root elongation in Scout 66 but not in Atlas 66. It also decreased the mechanical extensibility of the cell wall in the roots of both cultivars, but prominently only in the roots of Scout 66. The amount of hemicellulose in the 10-mm region of root apex of Scout 66 was increased by the exposure to Al, especially in the apical regions. Al did not influence the neutral sugar composition of either pectin or hemicellulose in Scout 66 roots. However, Al increased the weight-average molecular mass of hemicellulosic polysaccharides and the amounts of wall-bound ferulic and diferulic acids in Scout 66 roots. These findings suggest that Al modifies the metabolism of cell-wall components and thus makes the cell wall thick and rigid, thereby inhibiting the growth of wheat roots.

Differential distribution of lumican and fibromodulin in tooth cementum.

The objectives of this study were to isolate and characterize the major proteoglycans of tooth cementum in relation to the tissue's mineralization. Cementum was collected from the root apex region of bovine molars and pulverized. It was first extracted with 6M guanidine-HCI, pH 7.4 (G-extract, mineral-unassociated) and then demineralized and extracted with 0.5M EDTA (E-extract, mineral-associated). Both extracts were applied to anion exchange and then molecular sieve chromatography to isolate proteoglycans. The fractions collected were assayed for chondroitin-(CS) and keratan sulfate (KS) containing proteoglycans using the monoclonal antibodies 2-B-6 and 5-D-4, respectively. It was found that the KS was the major glycosaminoglycan and was enriched in the G-extract fraction. The major KS fraction was then applied to 7.5% SDS-PAGE. The major broad band (69 kDa) was 5-D-4 positive in Western blot analysis and separated into two bands (46 kDa and 50 kDa) after treatment with keratanase II and endo-beta-galactosidase. These two proteins were transfered to PVDF membrane and analyzed for amino acid sequence. The results showed the major band (46 kDa) to be lumican and the minor (50 kDa) fibromodulin. In addition, based on the immunohistochemical study using a number of mono- and polyclonal antibodies including 5-D-4, anti-lumican core protein as well as anti-fibromodulin core protein antibodies, the KSPGs were found to be located almost exclusively in nonmineralized portions of cementum such as precementum and the pericementocyte area. These biochemical as well as immunohistochemical data suggest that the major KSPGs of cementum, lumican and fibromodulin, have a specific tissue distribution and may have regulatory roles in cementum mineralization.