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PubMed1996

An Ethylene-Mediated Increase in Sensitivity to Auxin Induces Adventitious Root Formation in Flooded Rumex palustris Sm.

The hormonal regulation of adventitious root formation induced by flooding of the root system was investigated in the wetland species Rumex palustris Sm. Adventitious root development at the base of the shoot is an important adaptation to flooded conditions and takes place soon after the onset of flooding. Decreases in either endogenous auxin or ethylene concentrations induced by application of inhibitors of either auxin transport or ethylene biosynthesis reduced the number of adventitious roots formed by flooded plants, suggesting an involvement of these hormones in the rooting process. The rooting response during flooding was preceded by increased endogenous ethylene concentrations in the root system. The endogenous auxin concentration did not change during flooding-induced rooting, but a continuous basipetal transport of auxin from the shoot to the rooting zone appeared to be essential in maintaining stable auxin concentrations. These results suggest that the higher ethylene concentration in soil-flooded plants increases the sensitivity of the root-forming tissues to endogenous indoleacetic acid, thus initiating the formation of adventitious roots.

Journal Article↗
PubMed2001

Root hair initiation is coupled to a highly localized increase of xyloglucan endotransglycosylase action in Arabidopsis roots.

Root hairs are formed by two separate processes: initiation and subsequent tip growth. Root hair initiation is always accompanied by a highly localized increase in xyloglucan endotransglycosylase (XET) action at the site of future bulge formation, where the trichoblast locally loosens its cell wall. This suggests an important role of XET in the first stages of root hair initiation. The tip of growing root hairs is not marked by localized high XET action. Experiments in which root hair initiation was modulated and observations on root hair mutants support this view. The ethylene precursor 1-aminocyclopropane-1-carboxylic acid shifts both root hair initiation and the local increase in XET action toward the root tip. On the other hand, roots treated with the ethylene inhibitor aminoethoxyvinyl-glycine, as well as roots of mutants affected in root hair initiation (rhl1, rhd6-1, and axr2-1) revealed no localized increases of XET action at all and consequently did not initiate root hairs. Disruption of actin and microtubules did not prevent the localized increase in XET action. Also, the temporal and spatial pattern of action as the specific pH dependence suggest that different isoforms of XET act in different processes of root development.

Actins↗
PubMed1989

Hertwig's epithelial root sheath differentiation and initial cementum and bone formation during long-term organ culture of mouse mandibular first molars using serumless, chemically-defined medium.

Studies were designed to test the hypothesis that Hertwig's epithelial root sheath (HERS) synthesizes and secretes enamel-related proteins that participate in the process of acellular cementum formation. Our experimental strategy was to examine sequential root development of the mouse mandibular first molar in vivo and in long-term organ culture in vitro using serumless, chemically-defined medium. Using anti-amelogenin, anti-enamelin and anti-peptide antibodies, enamel-related antigens were localized within intermediate cementum during HERS differentiation and root formation in vivo. Cap stage molars maintained for periods of up to 31 days in organ culture expressed morphogenesis and cytodifferentiation as identified by tooth crown and initial root, cementum and bone formation. Metabolically-labeled HERS products were analyzed by immunodetection using enamel-related antibodies and one- and two-dimensional SDS gel electrophoresis. A 72 kDa and 26 kDa polypeptide were identified in forming mouse cementum. Both of these root putative cementum proteins yield similar (identical) amino acid compositions; however, both proteins differed from the compositions of either mouse crown enamelin or amelogenin proteins. This approach provides a new and novel in vitro model towards understanding HERS differentiation and functions related to root and bone formation. The data support the hypothesis that HERS cells synthesize polypeptides related to but also different from canonical crown enamel proteins.

Animals↗
PubMed2002

An 18-month longitudinal study on a new silicon-based sealer, RSA RoekoSeal: a leakage study in vitro.

OBJECTIVE: Because leakage along root fillings may increase or decrease during the long period after filling, the accumulated leakage data measured repeatedly after filling are clinically more relevant than the data measured just once shortly after filling. The aim of this study was to determine the long-term sealing ability of a recently developed root canal sealer RSA RoekoSeal (Roeko Dental Products, Langenau, Germany). STUDY DESIGN: Eighty extracted human mandibular premolars were equally divided into 4 groups (n = 20) and root canal instrumented. Canals in group 1 were obturated with laterally compacted gutta-percha points and RSA, in groups 2 to 4 with vertically compacted warm gutta-percha using RSA in group 2, Pulp Canal Sealer (Kerr, Romulus, Mich) in group 3, and no sealer in group 4. With the use of a fluid transport model, leakage along entire root fillings was measured before post space preparation. After post space preparation, leakage along the remaining apical root fillings was measured repeatedly at 1 week, 1, 2, 6, 12, and 18 months respectively and recorded in microliters per day. RESULTS: Before post space preparation, groups 1 and 2 leaked significantly less than groups 3 and 4 (P = .001), whereas no significant difference existed between the groups 1 and 2 (P = .317) or between the groups 3 and 4 (P = .074). For each group, a summation of the leakage at all time intervals after the post space preparation showed that the 2 RSA groups leaked significantly less than the other 2 groups (P =.000). However, no significant difference existed between the 2 RSA groups (P = .993) and between the groups 3 and 4 (P = .149). CONCLUSION: RSA used in combination with either cold laterally compacted or warm vertically compacted gutta-percha provided a consistent seal during a period of 18 months.

Bicuspid↗
PubMed2003

Dual genetic pathways controlling nodule number in Medicago truncatula.

We report the isolation and characterization of a new Medicago truncatula hyper-nodulation mutant, designated sunn (super numeric nodules). Similar to the previously described ethylene-insensitive mutant sickle, sunn exhibits a 10-fold increase in the number of nodules within the primary nodulation zone. Despite this general similarity, these two mutants are readily distinguished based on anatomical, genetic, physiological, and molecular criteria. In contrast to sickle, where insensitivity to ethylene is thought to be causal to the hyper-nodulation phenotype (R.V. Penmetsa, D.R. Cook [1997] Science 275: 527-530), nodulation in sunn is normally sensitive to ethylene. Nevertheless, sunn exhibits seedling root growth that is insensitive to ethylene, although other aspects of the ethylene triple response are normal; these observations suggest that hormonal responses might condition the sunn phenotype in a manner distinct from sickle. The two mutants also differ in the anatomy of the nodulation zone: Successful infection and nodule development in sunn occur predominantly opposite xylem poles, similar to wild type. In sickle, however, both infection and nodulation occur randomly throughout the circumference of the developing root. Genetic analysis indicates that sunn and sickle correspond to separate and unlinked loci, whereas the sunn/skl double mutant exhibits a novel and additive super-nodulation phenotype. Taken together, these results suggest a working hypothesis wherein sunn and sickle define distinct genetic pathways, with skl regulating the number and distribution of successful infection events, and sunn regulating nodule organogenesis.

Ethylenes↗
PubMed1984

Access cavity preparation.

The endodontic access cavity is an essential component of the endodontic triad upon which all subsequent canal preparation and filling is based. It is probably the most frequently underemphasized aspect of endodontic therapy. This results in great clinical frustration and poor immediate and long-term results for the practitioner. The access cavity must provide clear and unobstructed access to each and every orifice and must be designed in such a way so as not to interfere with the often difficult intracanal procedures to follow. An understanding of root development, chamber, and canal anatomy will allow the practitioner to more easily debride and seal each canal through proper access cavity preparation.

Dental Pulp Cavity↗
PubMed1994

Evidence for an essential role of the sucrose transporter in phloem loading and assimilate partitioning.

Sucrose is the principal transport form of assimilates in most plants. In many species, translocation of assimilates from the mesophyll into the phloem for long distance transport is assumed to be carrier mediated. A putative sucrose proton cotransporter cDNA has been isolated from potato and shown to be expressed mainly in the phloem of mature exporting leaves. To study the in vivo role and function of the protein, potato plants were transformed with an antisense construct of the sucrose transporter cDNA under control of the CaMV 35S promoter. Upon maturation of the leaves, five transformants that expressed reduced levels of sucrose transporter mRNA developed local bleaching and curling of leaves. These leaves contained > 20-fold higher concentrations of soluble carbohydrates and showed a 5-fold increase in starch content as compared with wild type plants, as expected from a block in export. Transgenic plants with a reduced amount of sucrose carrier mRNA show a dramatic reduction in root development and tuber yield. Maximal photosynthetic activity was reduced at least in the strongly affected transformants. The effects observed in the antisense plants strongly support an apoplastic model for phloem loading, in which the sucrose transporter located at the phloem plasma membrane represents the primary route for sugar uptake into the long distance distribution network.

Biological Transport↗
PubMed2003

Xyloglucan endotransglucosylase action is high in the root elongation zone and in the trichoblasts of all vascular plants from Selaginella to Zea mays.

The endotransglucosylase action of the enzyme xyloglucan endotransglucosylase/hydrolase (XTH) was localized in the roots of diverse vascular plants: club-mosses (lycopodiophytes), ferns, gymnosperms, monocots, and dicots. High action was always found in the epidermis cell wall of the elongation zone and in trichoblasts in the differentiation zone. Clearly XTH and its action in root development evolved before the evolutionary divergence of ferns and seed plants and also of the lycopodiophytes and euphyllophytes.

Cycadopsida↗
PubMed1997

An evaluation of after-office-hour dental trauma in Singapore.

The purpose of this study was to assess the post-traumatic sequelae and treatment outcome and the corresponding prognostic factors at the initial emergency visit. Over a 5-year period, the authors collected case records from 129 dental trauma patients. These patients had been referred subsequent to receiving emergency treatment after office hours at the Accident and Emergency Department of Singapore General Hospital. After the exclusion of 31 cases with concomitant fracture of maxilla and/or mandible and cases with insufficient documentation, the final study sample consisted of 98 patients (41 males, 57 females) who had sustained injuries to 264 permanent teeth. The main cause of dental trauma was falls (56%), and the main type of injuries was periodontal tissue injuries with or without concomitant injuries to hard tissue, including root fracture (73%). For the final evaluation, teeth with insufficient recall period were excluded before univariate and multivariate stepwise logistic regression analysis. It was found that for 100 teeth with luxation type of injuries, the presence of concomitant hard tissue injuries retained prognostic significance for pulpal outcome (p < 0.001) after adjusting for severity of luxation, while the severity of luxation was the only significant factor for periodontal outcome (p < 0.001). For 34 avulsed teeth, the stage of root development was the major factor associated with the pulpal outcome (p = 0.003), while extra-alveolar storage media were found to be significantly related to the periodontal outcome (p < 0.001). For 72 teeth with hard tissue injuries, first-visit interval played a significant role in the outcome (p = 0.03). Although the sample size in the root fracture group was too small for such statistical analysis, the results indicated that patient education on dental trauma was an important factor. Thorough standardized documentation was also recommended to facilitate optimal follow-up management and future research as well as medico-legal purposes.

Adolescent↗
PubMed1999

Osmotic water permeability of isolated protoplasts. Modifications during development

A transference chamber was developed to measure the osmotic water permeability coefficient (Pos) in protoplasts 40 to 120 μm in diameter. The protoplast was held by a micropipette and submitted to a steep osmotic gradient created in the transference chamber. Pos was derived from the changes in protoplast dimensions, as measured using a light microscope. Permeabilities were in the range 1 to 1000 μm s-1 for the various types of protoplasts tested. The precision for Pos was </=40%, and within this limit, no asymmetry in the water fluxes was observed. Measurements on protoplasts isolated from 2- to 5-d-old roots revealed a dramatic increase in Pos during root development. A shift in Pos from 10 to 500 μm s-1 occurred within less than 48 h. This phenomenon was found in maize (Zea mays), wheat (Triticum aestivum), and rape (Brassica napus) roots. These results show that early developmental processes modify water-transport properties of the plasma membrane, and that the transference chamber is adapted to the study of water-transport mechanisms in native membranes.

Journal Article↗
PubMed1998

Maxillary dental development in complete unilateral alveolar clefts.

OBJECTIVE: This study was conducted to determine whether development of individual maxillary teeth in subjects with complete unilateral alveolar clefts was significantly different from that found in unaffected children. DESIGN: Retrospective, mixed longitudinal. SETTING: Craniofacial Center, university based. MATERIALS AND METHODS: A sample of 179 panoramic radiographs obtained during the mixed dentition from 79 subjects (47 males, 32 females) with complete alveolar clefts was analyzed. After visual evaluation of root development of the permanent maxillary teeth from radiographs, a score from 0 to 5 was assigned utilizing a predefined scoring system. Statistical analyses were performed between the cleft and unaffected reference groups available in the literature. RESULTS: The cleft side dentition was found to be significantly delayed in development relative to the noncleft side (p < .05). Compared to the reference group, the cleft side lateral incisor demonstrated a mean difference in development of 1.59 years followed by the canine (1.39 years), the central incisor (0.96 years), the first premolar (0.94), and the second premolar (0.78). CONCLUSION: Teeth directly adjacent to the cleft site were shown to be the most delayed. The lateral incisors and canines were observed to be the most variable when compared to their corresponding antimeres. The information obtained from this study may assist the orthodontist in selecting the appropriate time to initiate orthodontic treatment in order to prepare the permanent dentition prior to alveolar bone grafting.

Adolescent↗
PubMed2001

Flavonoids act as negative regulators of auxin transport in vivo in arabidopsis.

Polar transport of the plant hormone auxin controls many aspects of plant growth and development. A number of synthetic compounds have been shown to block the process of auxin transport by inhibition of the auxin efflux carrier complex. These synthetic auxin transport inhibitors may act by mimicking endogenous molecules. Flavonoids, a class of secondary plant metabolic compounds, have been suggested to be auxin transport inhibitors based on their in vitro activity. The hypothesis that flavonoids regulate auxin transport in vivo was tested in Arabidopsis by comparing wild-type (WT) and transparent testa (tt4) plants with a mutation in the gene encoding the first enzyme in flavonoid biosynthesis, chalcone synthase. In a comparison between tt4 and WT plants, phenotypic differences were observed, including three times as many secondary inflorescence stems, reduced plant height, decreased stem diameter, and increased secondary root development. Growth of WT Arabidopsis plants on naringenin, a biosynthetic precursor to those flavonoids with auxin transport inhibitor activity in vitro, leads to a reduction in root growth and gravitropism, similar to the effects of synthetic auxin transport inhibitors. Analyses of auxin transport in the inflorescence and hypocotyl of independent tt4 alleles indicate that auxin transport is elevated in plants with a tt4 mutation. In hypocotyls of tt4, this elevated transport is reversed when flavonoids are synthesized by growth of plants on the flavonoid precursor, naringenin. These results are consistent with a role for flavonoids as endogenous regulators of auxin transport.

Alleles↗
PubMed2000

Carbon and nitrogen mobilization in Larix x eurolepis leafy stem cuttings assessed by dual (13)C and (15)N labeling: relationships with rooting.

Changes in use of both stored and newly synthesized sources of carbon (C) and nitrogen (N) were investigated during rooting of leafy cuttings of Larix x eurolepis A. Henry. We used dual (13)C and (15)N long-term labeling of reserves of stock plants and followed isotope dilution of the labels in the cuttings to determine the respective proportions of C and N derived from stock plant reserves (Q(C,old), Q(N,old)) and from newly synthesized sources (Q(C,new), Q(N,new)). We also assessed their partitioning into the growing needles and roots. Because rooting development occurred over several months, destructive harvests were made during three periods (t(0): April 9; t(1): May 15 to June 5; t(2): June 12 to June 26). Total C content (Q(C)) of cuttings did not change with time, whereas total N content (Q(N)) decreased significantly between t(0) and t(2). In rooted cuttings, unlike unrooted cuttings, total N concentration decreased less markedly in needles and in the lower stem component between t(1) and t(2) than between t(0) and t(2). The lower stem of rooted cuttings contained more Q(N,old) than that of unrooted cuttings and showed lower C:N and (13)C:(15)N ratios. The increase in Q(N,new) in the lower stem was positively correlated with rooting status. At t(1), new roots appeared and grew mainly at the expense of Q(C,new) and Q(N,old). By t(2), root growth was mainly dependent on new assimilates. We conclude that in leafy cuttings the initial amount of N reserves, rather than C reserves, may constitute a limiting factor for rooting.

Journal Article↗
PubMed2003

Arabidopsis actin gene ACT7 plays an essential role in germination and root growth.

Arabidopsis contains eight actin genes. Of these ACT7 is the most strongly expressed in young plant tissues and shows the greatest response to physiological cues. Adult plants homozygous for the act7 mutant alleles show no obvious above-ground phenotypes, which suggests a high degree of functional redundancy among plant actins. However, act7-1 mutant plants are at a strong selective disadvantage when grown in competition with wild-type plants and therefore must have undetected physical defects. The act7-1 and act7-4 alleles contain T-DNA insertions just after the stop codon and within the first intron, respectively. Homozygous mutant seedlings of both alleles showed less than 7% of normal ACT7 protein levels. Mutants displayed delayed and less efficient germination, increased root twisting and waving, and retarded root growth. The act7-4 mutant showed the most dramatic reduction in root growth. The act7-4 root apical cells were not in straight files and contained oblique junctions between cells suggesting a possible role for ACT7 in determining cell polarity. Wild-type root growth was fully restored to the act7-1 mutant by the addition of an exogenous copy of the ACT7 gene. T-DNA insertions just downstream of the major polyadenylation sites (act7-2, act7-3) appeared fully wild type. The act7 mutant phenotypes demonstrate a significant requirement for functional ACT7 protein during root development and explain the strong negative selection component seen for the act7-1 mutant.

Actins↗
PubMed1996

Methods of reducing observer variation in age estimation from panoramic radiographs.

OBJECTIVE: To compare inter- and intra-observer variation in age estimation using subjective and objective methods. METHODS: Fifty-six panoramic radiographs of patients aged 13 to 25 years were assessed subjectively twice by four observers for the stage of root development of the lower third molars on a seven-point scale. Two of the observers were calibrated before the first evaluation, and the other two before the second. The same observers also digitized predefined reference points in a subsample of the third molars ten times by means of a computer-based digitizer system. Observer variation in classifying different root stages and in digitizing coordinates and measuring root lengths were studied. RESULTS: Significant systematic differences existed between two of the observers in the subjective assessment. One non-pre-calibrated observer changed her pattern most. Scattergrams from the digitizer measurements showed a good precision within and between observers with no significant differences in calculating root lengths. When, however, the teeth were analysed separately, some significant differences were found. CONCLUSIONS: The overall observer agreement was best using the objective method on several teeth. With only one tooth there were some significant differences. Subjective evaluation was improved by prior calibration.

Adolescent↗
PubMed1993

Histological reconstruction of dental development and age at death of a juvenile Paranthropus robustus specimen, SK 63, from Swartkrans, South Africa.

There has been disagreement about whether the earliest hominids grew in a similar manner to great apes or modern humans. This has important biological implications, since it may have been inappropriate to apply modern human developmental standards to early hominids. The aim of the present study was to combine data from replicas of tooth surfaces, computed tomographic (CT) scans, and radiographs with data from a histological section of the canine crown, in order to provide a complete description of tooth crown and tooth root development in a single early hominid specimen (SK 63). Although partially destructive in nature, we have been able to determine the most reliable data yet for aspects of dental development in an important juvenile early hominid specimen. Appositional enamel formation time in the permanent right canine was estimated at between 305 and 418 days, imbricational enamel formation time at 819 days, and total crown formation time at between 3.18 and 3.48 years. The most likely age at death was estimated at around 4 years with a range of ages calculated between 3.18 and 4.23 years based on differences in timing of initial mineralization of the canine and differences in appositional enamel formation times. Crown formation times of the lower central and lateral incisors were estimated between 2.35-2.68 years and 2.57-2.91 years, respectively. Crown formation time of the first permanent molar was estimated at 2.4 years. Wear facets on the first permanent molars indicate that gingival emergence had occurred sometime prior to death, between 3 and 4 years of age. Estimates of root extension rates in the first permanent molars and in the permanent incisors are fast, and either within or above ranges of rates estimated for modern great apes. While we recognize that data for one individual may not be representative of data for a whole population of early hominids, the data for age at death, for age of M1 emergence, and for root extension rates presented here accord with those known for modern great apes and fall beyond the known ranges for modern humans.

Age Determination by Teeth↗
PubMed1995

Cellular and molecular events in a newly organizing lateral root meristem.

Spontaneous or auxin-induced lateral root formation in radish and Arabidopis provides an efficient system in which to examine molecular and cellular events associated with the initiation of a new meristem. Subtracted cDNA libraries made at different times in lateral root initiation were used as a source of genes that are expressed differentially during this developmental process, and expression studies on a small gene family of ribosomal protein genes were conducted. From analysis of cell division patterns in pericycle cells the number of founder cells for lateral roots was established. By the use of in vitro growth assays lateral root formation was determined to be a two-stage process. First a primordium is formed, and subsequently a subset of primordial cells begins to function as the lateral root apical meristem. This mode of root development has implications for pattern formation in newly organizing organs.

Arabidopsis↗
PubMed1997

Characterization of the common bean uricase II and its expression in organs other than nodules.

Uricase II is a purine metabolic enzyme highly induced in root nodules during the symbiosis established between legumes and bacteria of the genera Rhizobium and Bradyrhizobium. Here we describe the characterization of bean (Phaseolus vulgaris) nodule uricase II cDNA and show that uricase II is encoded by a single gene in the bean genome. This gene is also expressed in cotyledons, roots, and hypocotyls during bean seedling establishment, and an anti-uricase antibody recognizes the protein in different seedling organs. Uricase II has also been found in Leucaena leucocephala seedlings, suggesting that it participates during seedling establishment in legumes that do not transport ureides. A 50-kD polypeptide that is detected by the anti-uricase antibody is found in cotyledons during seedling development. This higher-molecular-mass form is also detected in developing roots and hypocotyls but not in nodules. In situ hybridization experiments in root seedlings showed uricase II transcripts in the metaxylem parenchyma cells and phloem fibers of the vascular system.

Amino Acid Sequence↗