SEARCH · Search PubMed

Results for “root”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,729 records · Page 96Linked to original sources

PubMed2003

Diffusion of an organic cation into root cell walls.

Uptake of a cationic dye (methylene blue) by isolated root cell walls, roots of whole transpiring seedlings, and excised roots was investigated using 7-day-old seedlings of cucumber, maize, and wheat. The number of ionogenic groups per 1 g dry and wet weight of the root cell walls, their swelling capacity (K(cw)), time-dependence of methylene blue (M(cw)) ion exchange capacity, and diffusion coefficients of the cation diffusion in the polymer matrix of the cell walls (D(cw)) were determined. The M(cw) value depended on pH (or carboxyl group dissociation); it changed in accordance with the number of carboxyl groups per 1 g cell wall dry weight. This parameter decreased in the order: cucumber > wheat > maize. For description of experimental kinetic curves and calculation of cation diffusion coefficients, the equation for ion diffusion into a cylinder of infinite length was used. The chosen model adequately described cation diffusion in cell walls and roots. Diffusion coefficient values for cucumber, wheat, and maize were 3.1*10(-8), 1.3*10(-8), and 8.4*10(-8) cm(2)/sec, respectively. There was a statistically significant linear dependence between K(cw) and D(cw) values, which characterize the same property of the polymer matrix, rigidity of its polymer structure or the degree of cross-linkage or permeability. This also confirms the right choice of the model selected for calculation of methylene blue diffusion coefficients, because K(cw) and D(cw) values were obtained in independent experiments. The coefficients determined for methylene blue diffusion in transpiring seedling roots (D(ts)) and excised roots (D(er)) depended on the plant species. The rate of methylene blue diffusion into the excised roots was either 1.5-fold lower (cucumber) or 3-4-times lower (maize, wheat) than in cell walls. The values of diffusion coefficients in roots of whole seedlings were comparable which those for the cell walls. On the basis of the experimental data and results of calculations, it is concluded that the mechanism of methylene blue uptake by plant roots involves ion exchange reactions between the organic cation and cell wall carboxyl groups, and the uptake rate is determined by the cation diffusion in the polymer matrix of the cell walls.

Biological Transport↗

PubMed2003

Growth and cell wall changes in rice roots during spaceflight.

We analyzed the changes in growth and cell wall properties of roots of rice (Oryza sativa L. cv. Koshihikari) grown for 68.5, 91.5, and 136 h during the Space Shuttle STS-95 mission. In space, most of rice roots elongated in a direction forming a constant mean angle of about 55 degrees with the perpendicular base line away from the caryopsis in the early phase of growth, but later the roots grew in various directions, including away from the agar medium. In space, elongation growth of roots was stimulated. On the other hand, some of elasticity moduli and viscosity coefficients were higher in roots grown in space than on the ground, suggesting that the cell wall of space-grown roots has a lower capacity to expand than the controls. The levels of both cellulose and the matrix polysaccharides per unit length of roots decreased greatly, whereas the ratio of the high molecular mass polysaccharides in the hemicellulose fraction increased in space-grown roots. The prominent thinning of the cell wall could overwhelm the disadvantageous changes in the cell wall mechanical properties, leading to the stimulation of elongation growth in rice roots in space. Thus, growth and the cell wall properties of rice roots were strongly modified under microgravity conditions during spaceflight.

Cell Wall↗

PubMed2002

Shoot-derived auxin is essential for early lateral root emergence in Arabidopsis seedlings.

Lateral root formation is profoundly affected by auxins. Here we present data which indicate that light influences the formation of indole-3-acetic acid (IAA) in germinating Arabidopsis seedlings. IAA transported from the developing leaves to the root system is detectable as a short-lived pulse in the roots and is required for the emergence of the lateral root primordia (LRP) during early seedling development. LRP emergence is inhibited by the removal of apical tissues prior to detection of the IAA pulse in the root, but this treatment has minimal effects on LRP initiation. Our results identify the first developing true leaves as the most likely source for the IAA required for the first emergence of the LRP, as removal of cotyledons has only a minor effect on LRP emergence in contrast to removal of the leaves. A basipetal IAA concentration gradient with high levels of IAA in the root tip appears to control LRP initiation, in contrast to their emergence. A significant increase in the ability of the root system to synthesize IAA is observed 10 days after germination, and this in turn is reflected in the reduced dependence of the lateral root emergence on aerial tissue-derived auxin at this stage. We propose a model for lateral root formation during early seedling development that can be divided into two phases: (i) an LRP initiation phase dependent on a root tip-localized IAA source, and (ii) an LRP emergence phase dependent on leaf-derived IAA up to 10 days after germination.

Arabidopsis↗

PubMed2001

Effect of access cavity location and design on degree and distribution of instrumented root canal surface in maxillary anterior teeth.

AIM: The null hypothesis tested in this study was that in single-rooted anterior teeth with simple root canal anatomy, different access cavity designs ('lingual cingulum', 'lingual conventional', 'incisal straight-line') do not influence the ability of endodontic files to plane the walls of the root canals. METHODOLOGY: Thirty extracted human maxillary anterior teeth were divided randomly into three groups for each access cavity. The access cavities were prepared according to predefined criteria and the roots embedded in individual polyvinyl-siloxane putty matrices. The matrices allowed these teeth to be split into buccal and palatal halves and to be reassembled. The split teeth enabled removal of pulpal remnants from the root canal system and the walls to be stained with an even layer of permanent black ink. Once dried, the split roots were reassembled in the putty matrices and a step-back filing technique was used to prepare the canals with water irrigation. The canal walls were examined for residual ink staining and scored by three independent assessors using an index devised for the purpose. RESULTS: There was good agreement between the assessors. None of the access cavities allowed file contact with the entire root canal wall. The overall (palatal and buccal sections) scores showed significant differences (P < 0.01) between the access cavity groups in the extent to which the canal walls could be filed. The straight-line incisal access cavity had the greatest proportion of instrumented root canal surface. The lingual cingulum access cavity was the worst in this respect. The differences in residual ink scores between the access cavity types were significant for the buccal halves (P < 0.01) but not for the palatal halves (P > 0.05). CONCLUSIONS: The null hypothesis was proven. Regardless of access cavity design, mechanical preparation did not allow instrumentation of the entire root canal wall. Straight-line access allowed the greatest proportion of the root canal wall to be instrumented and the lingual cingulum access the least.

Chi-Square Distribution↗

PubMed2003

Four-dimensional imaging and computer-assisted track analysis of nuclear migration in root hairs of Arabidopsis thaliana.

Nuclear migration is a fundamental mechanism necessary for the proper growth and development of many eukaryotic organisms. In this study root hairs of Arabidopsis thaliana were used as a research model to gain insight into the dynamics of nuclear migration. Root hairs are long tubular outgrowths of epidermal cells and are responsible for the uptake of water and nutrients. During the development of root hairs, the nucleus migrates into the hair after the bulge is formed. The position of the nucleus relative to the tip plays an essential role in the growth process. However, what is happening to the nucleus in full-grown root hairs is still unclear. To study nuclear dynamics in living root hair cells, stably transformed plants with the fusion proteins Histone2B-YFP and NLS-GFP-GUS were used. Four-dimensional confocal laser scanning microscopy made it possible to monitor the exact position of the nucleus in different root hairs. To analyse the sequential positions of the nuclei in the root hairs, a new computer-assisted method was developed. After track analysis a number of parameters could be extracted from the movies, such as the average speed, the amplitude, direction factor and the range of movement in the root hairs. Our results show that nuclei do not reach a final position in full-grown root hairs and this sustained movement seems to be more similar in root hairs lying close to each other. Moreover, with this methodology it could be quantitatively demonstrated that the integrity of actin is necessary for nuclear movement.

Arabidopsis↗

PubMed1997

Novel software for analysis of root gravitropism: comparative response patterns of Arabidopsis wild-type and axr1 seedlings.

In an earlier study (Evans, Ishikawa & Estelle 1994, Planta 194, 215-222) we used a video digitizer system to compare the kinetics of auxin action on root elongation in wild-type seedlings and seedlings of auxin response mutants of Arabidopsis thaliana (L.) Heynh. We have since modified the system software to allow determination of elongation on opposite sides of vertical or gravistimulated roots and to allow continuous measurement of the angle of orientation of sequential subsections of the root during the response. We used this technology to compare the patterns of differential growth that generate curvature in roots of the Columbia ecotype and in the mutants axr1-3, axr1-12 and axr2, which show reduced gravitropic responsiveness and reduced sensitivity to inhibition by auxin. The pattern of differential growth during gravitropism differed in roots of wild-type and axr1 seedlings. In wild-type roots, initial curvature resulted from differential inhibition of elongation in the distal elongation zone (DEZ). This was followed by an acceleration of elongation along the top side of the DEZ. In roots of axr1-3, curvature resulted from differential stimulation of elongation whereas in roots of axr1-12 the response was variable. Roots of axr2 did not exhibit gravitropic curvature. The observation that the pattern of differential growth causing curvature is dramatically altered by a change in sensitivity to auxin is consistent with the classical Cholodny-Went theory of gravitropism which maintains that differential growth patterns induced by gravistimulation are mediated primarily by gravi-induced shifts in auxin distribution. The new technology introduced with this report allows automated determination of stimulus response patterns in the small but experimentally popular roots of Arabidopsis.

Arabidopsis↗

PubMed2001

Sulphate reduction and nitrogen fixation rates associated with roots, rhizomes and sediments from Zostera noltii and Spartina maritima meadows.

Sulphate reduction rates (SRR) and nitrogen fixation rates (NFR) associated with isolated roots, rhizomes and sediment from the rhizosphere of the marine macrophytes Zostera noltii and Spartina maritima, and the presence and distribution of Bacteria on the roots and rhizomes, were investigated. Between 1% and 3% of the surface area of the roots and rhizomes of both macrophytes were colonized by Bacteria. Bacteria on the surfaces of S. maritima roots and rhizomes were evenly distributed, while the distribution of Bacteria on Z. noltii roots and rhizomes was patchy. Root- and rhizome-associated SRR and NFR were always higher than rates in the bulk sediment. In particular, nitrogen fixation associated with the roots and rhizomes was 41-650-fold higher than in the bulk sediment. Despite the fact that sulphate reduction was elevated on roots and rhizomes compared with bulk sediment, the contribution of plant-associated sulphate reduction to overall sulphate reduction was small (< or =11%). In contrast, nitrogen fixation associated with the roots and rhizomes accounted for 31% and 91% of the nitrogen fixed in the rhizosphere of Z. noltii and S. maritima respectively. In addition, plant-associated nitrogen fixation could supply 37-1,613% of the nitrogen needed by the sulphate-reducing community. Sucrose stimulated nitrogen fixation and sulphate reduction significantly in the root and rhizome compartments of both macrophytes, but not in the bulk sediment.

Acetylene↗

PubMed2002

Persistence of Escherichia coli O157:H7 in soil and on plant roots.

Soil microcosms were inoculated with Escherichia coli O157:H7 to test persistence in fallow soil, on roots of cover crops and in presence of manure. In fallow soils, E. coli O157:H7 persisted for 25-41 days, on rye roots for 47-96 days and on alfalfa roots, in a silt loam soil, for 92 days whereas on other legumes persistence ranged from 25-40 days, similar to fallow soil. Manure did not seem to affect the persistence of E. coli O157:H7 in these soils. Indigenous and manure-applied coliform populations often decreased faster when E. coli O157:H7 was applied, indicating possible competition between microflora. Coliform populations in microcosms not inoculated with E. coli O157:H7 decreased more slowly or increased. Microbial community analyses showed little effect for E. coli O157:H7 inoculation or addition of manure. Microbial community metabolic activity was enhanced from rye roots after 14 days and by 63 days from alfalfa roots. Microbial community lactose utilization increased over time on rye roots in all soils and on alfalfa roots in a silt loam soil when E. coli O157:H7 was inoculated. Lactose utilization also increased for uninoculated rye roots, soil around rye roots and in some fallow soils. Our data suggest that clay increases persistence and activity of E. coli O157:H7 and other coliforms. In frozen soil stored for over 500 days, E. coli O157:H7 was viable in 37% of tested samples. In summary, E. coli O157:H7 persisted longer and activity was enhanced with some cover crops in these soils due to plant roots, the presence of clay and freezing.

Aluminum Silicates↗

PubMed2004

Fine-root production dominates response of a deciduous forest to atmospheric CO2 enrichment.

Fine-root production and turnover are important regulators of the biogeochemical cycles of ecosystems and key components of their response to global change. We present a nearly continuous 6-year record of fine-root production and mortality from minirhizotron analysis of a closed-canopy, deciduous sweetgum forest in a free-air CO(2) enrichment experiment. Annual production of fine roots was more than doubled in plots with 550 ppm CO(2) compared with plots in ambient air. This response was the primary component of the sustained 22% increase in net primary productivity. Annual fine-root mortality matched annual production, and the mean residence time of roots was not altered by elevated CO(2), but peak fine-root standing crop in midsummer was significantly higher in CO(2)-enriched plots, especially deeper in the soil profile. The preferential allocation of additional carbon to fine roots, which have a fast turnover rate in this species, rather than to stemwood reduces the possibility of long-term enhancement by elevated CO(2) of carbon sequestration in biomass. However, sequestration of some of the fine-root carbon in soil pools is not precluded, and there may be other benefits to the tree from a seasonally larger and deeper fine-root system. Root-system dynamics can explain differences among ecosystems in their response to elevated atmospheric CO(2); hence, accurate assessments of carbon flux and storage in forests in a globally changing atmosphere must account for this unseen and difficult-to-measure component.

Atmosphere↗

PubMed2006

The Arabidopsis NRT1.1 transporter participates in the signaling pathway triggering root colonization of nitrate-rich patches.

Localized proliferation of lateral roots in NO(3)(-)-rich patches is a striking example of the nutrient-induced plasticity of root development. In Arabidopsis, NO(3)(-) stimulation of lateral root elongation is apparently under the control of a NO(3)(-)-signaling pathway involving the ANR1 transcription factor. ANR1 is thought to transduce the NO(3)(-) signal internally, but the upstream NO(3)(-) sensing system is unknown. Here, we show that mutants of the NRT1.1 nitrate transporter display a strongly decreased root colonization of NO(3)(-)-rich patches, resulting from reduced lateral root elongation. This phenotype is not due to lower specific NO(3)(-) uptake activity in the mutants and is not suppressed when the NO(3)(-)-rich patch is supplemented with an alternative N source but is associated with dramatically decreased ANR1 expression. These results show that NRT1.1 promotes localized root proliferation independently of any nutritional effect and indicate a role in the ANR1-dependent NO(3)(-) signaling pathway, either as a NO(3)(-) sensor or as a facilitator of NO(3)(-) influx into NO(3)(-)-sensing cells. Consistent with this model, the NRT1.1 and ANR1 promoters both directed reporter gene expression in root primordia and root tips. The inability of NRT1.1-deficient mutants to promote increased lateral root proliferation in the NO(3)(-)-rich zone impairs the efficient acquisition of NO(3)(-) and leads to slower plant growth. We conclude that NRT1.1, which is localized at the forefront of soil exploration by the roots, is a key component of the NO(3)(-)-sensing system that enables the plant to detect and exploit NO(3)(-)-rich soil patches.

Anion Transport Proteins↗

PubMed2003

Long-distance root-to-shoot transport of phytochelatins and cadmium in Arabidopsis.

Phytochelatin synthases (PCS) mediate cellular heavy-metal resistance in plants, fungi, and worms. However, phytochelatins (PCs) are generally considered to function as intracellular heavy-metal detoxification mechanisms, and whether long-distance transport of PCs occurs during heavy-metal detoxification remains unknown. Here, wheat TaPCS1 cDNA expression was either targeted to Arabidopsis roots with the Arabidopsis alcohol dehydrogenase (Adh) promoter (Adh::TaPCS1/cad1-3) or ectopically expressed with the cauliflower mosaic virus 35S promoter (35S::TaPCS1/cad1-3) in the PC-deficient mutant cad1-3. Adh::TaPCS1/cad1-3 and 35S::TaPCS1/cad1-3 complemented the cadmium, mercury, and arsenic sensitivities of the cad1-3 mutant. Northern blot, RT-PCR, and Western blot analyses showed Adh promoter-driven TaPCS1 expression only in roots and thus demonstrated lack of long-distance TaPCS1 mRNA and protein transport in plants. Fluorescence HPLC analyses showed that under Cd2+ stress, no PCs were detectable in cad1-3. However, in Adh::TaPCS1/cad1-3 plants, PCs were detected in roots and in rosette leaves and stems. Inductively coupled plasma atomic emission spectrometer analyses showed that either root-specific or ectopic expression of TaPCS1 significantly enhanced long-distance Cd2+ transport into stems and rosette leaves. Unexpectedly, transgenic expression of TaPCS1 reduced Cd2+ accumulation in roots compared with cad1-3. The reduced Cd2+ accumulation in roots and enhanced root-to-shoot Cd2+ transport in transgenic plants were abrogated by l-buthionine sulfoximine. The presented findings show that (i) transgenic expression of TaPCS1 suppresses the heavy-metal sensitivity of cad1-3, (ii) PCs can be transported from roots to shoots, and (iii) transgenic expression of the TaPCS1 gene increases long-distance root-to-shoot Cd2+ transport and reduces Cd2+ accumulation in roots.

Aminoacyltransferases↗

PubMed1996

Preferential expression of an ammonium transporter and of two putative nitrate transporters in root hairs of tomato.

Root hairs as specialized epidermal cells represent part of the outermost interface between a plant and its soil environment. They make up to 70% of the root surface and, therefore, are likely to contribute significantly to nutrient uptake. To study uptake systems for mineral nitrogen, three genes homologous to Arabidopsis nitrate and ammonium transporters (AtNrt1 and AtAmt1) were isolated from a root hair-specific tomato cDNA library. Accumulation of LeNrt1-1, LeNrt1-2, and LeAmt1 transcripts was root-specific, with no detectable transcripts in stems or leaves. Expression was root cell type-specific and regulated by nitrogen availability. LeNrt1-2 mRNA accumulation was restricted to root hairs that had been exposed to nitrate. In contrast, LeNrt1-1 transcripts were detected in root hairs as well as other root tissues under all nitrogen treatments applied. Analogous to LeNrt1-1, the gene LeAmt1 was expressed under all nitrogen conditions tested, and root hair-specific mRNA accumulation was highest following exposure to ammonium. Expression of LeAMT1 in an ammonium uptake-deficient yeast strain restored growth on low ammonium medium, confirming its involvement in ammonium transport. Root hair specificity and characteristics of substrate regulation suggest an important role of the three genes in uptake of mineral nitrogen.

Amino Acid Sequence↗

PubMed1951

After-currents, after-potentials, excitability, and ventral root electrotonus in spinal motoneurons.

The spinal cord constitutes a volume conductor. Potential changes are recorded therefrom only as current flows. During the period of the after-potentials current flows in significant density only if the after-polarization differs at different points of the active neurons. Thus one does not record after-potentials in volume; one may record after-currents which are defined as the resultants of differences in after-potentials. Measurable excitability change during the period of the after-potentials, in the event no current flows, might be regarded as approximating the change of intrinsic polarization status at the region tested. In the presence of after-current flow excitability change would approximate the sum of intrinsic change and extrinsic change due to current flow. In giving rise by differences to current flow after-potentials come to act as agents, and events in one part of a neuron help to determine excitability in other parts. Since the intramedullary after-current flow is not the after-potential of the soma, it follows that ventral root electrotonus which results from axonal after-current flow cannot be considered the counterpart of somatic after-potential. Following conduction of an antidromic volley after-current flows between somata and axons. According to the signs of the recorded potential changes, after-current flow initially, and for approximately 45 msec., is in the direction from somata to axons. Thereafter, and for approximately another 75 msec., the direction of flow is reversed. During the period of after-current flow following antidromic conduction the excitability of neighboring motoneurons is altered in a manner that reproduces the phases of after-current flow. The initial phase, depression, was first described by Renshaw. The after-potentials of ventral root fibers have been studied. In a single action and in usual form, they consist of a negative after-potential of considerable magnitude and of some 35 msec. duration, and a positive after-potential detectable for approximately 120 msec. Variants and the influence of temperature change are described. The recovery cycle of ventral root axons in general compares with the after-potential cycle. Recovery of intramedullary motor axons differs from that of their extramedullary projections as ventral root fibers in a manner that is accountable to intramedullary flow of after-current. Since the intrinsic recovery process of the motoneuron somata cannot be measured in the presence of current flow it must be estimated by correcting the observed recovery for the influence of known current flows. When this is done the resultant in simplest form provides for intrinsic somatic recovery from refractoriness through a single phase of subnormality lasting some 60 msec. Conditions for the relatively undistorted recording of antidromic ventral root electrotonus are described. They include provisions that the proximal ventral root electrode must be within 12 mm. of the root-cord junction and that the distal electrode must be located in excess of 30 mm. from the distal severed end of the ventral root. Antidromic ventral root electrotonus is a counterpart of the current flows in the intramedullary stretch of the axons. Initially, during the phase of metadromal postivity of the intramedullary axons, electrotonus is negative. During the period of deflections Sp-An, that signify after-current flow into the axons, electrotonus is positive. Finally during the period of deflections Sn-Ap, that signify after-current flow outwards through the intramedullary axon membranes, electrotonus is negative. Electrotonic showing is not of sufficient magnitude to make the time course of ventral root electrotonus palpably different from that of the generating intramedullary currents.

Axons↗

PubMed2001

Evidence of root zone hypoxia in Brassica rapa L. grown in microgravity.

A series of experiments was conducted aboard the U.S. space shuttle and the Mir space station to evaluate microgravity-induced root zone hypoxia in rapid-cycling Brassica (Brassica rapa L.), using both root and foliar indicators of low-oxygen stress to the root zone. Root systems from two groups of plants 15 and 30 d after planting, grown in a phenolic foam nutrient delivery system on the shuttle (STS-87), were harvested and fixed for microscopy or frozen for enzyme assays immediately postflight or following a ground-based control. Activities of fermentative enzymes were measured as indicators of root zone hypoxia and metabolism. Following 16 d of microgravity, ADH (alcohol dehydrogenase) activity was increased in the spaceflight roots 47% and 475% in the 15-d-old and 30-d-old plants, respectively, relative to the ground control. Cytochemical localization showed ADH activity in only the root tips of the space-grown plants. Shoots from plants that were grown from seed in flight in a particulate medium on the Mir station were harvested at 13 d after planting and quick-frozen and stored in flight in a gaseous nitrogen freezer or chemically fixed in flight for subsequent microscopy. When compared to material from a high-fidelity ground control, concentrations of shoot sucrose and total soluble carbohydrate were significantly greater in the spaceflight treatment according to enzymatic carbohydrate analysis. Stereological analysis of micrographs of sections from leaf and cotyledon tissue fixed in flight and compared with ground controls indicated no changes in the volume of protoplast, cell wall, and intercellular space in parenchyma cells. Within the protoplasm, the volume occupied by starch was threefold higher in the spaceflight than in the ground control, with a concomitant decrease in vacuolar volume in the spaceflight treatment. Both induction of fermentative enzyme activity in roots and accumulation of carbohydrates in foliage have been repeatedly shown to occur in response to root zone oxygen deprivation. These results indicate that root zone hypoxia is a persistent challenge in spaceflight plant growth experiments and may be caused by microgravity-induced changes in fluid and gas distribution.

Alcohol Dehydrogenase↗

PubMed2000

Gallium diffusion in human root dentin: quantitative measurements by pulsed Nd:YAG laser ablation combined with an inductively coupled plasma mass spectrometer.

OBJECTIVE: The purpose of this work was to determine if gallium nitrate placed in human root canals would diffuse across root dentin and reach concentrations high enough to inhibit osteoclasts (approximately 10(-4) M). BACKGROUND DATA: External root resorption by osteoclasts is a common sequela of dental trauma. If not detected and treated, it can lead to the loss of a tooth. Gallium has recently been reported to inhibit osteoclastic resorption in vitro. METHODS: Roots were cleaned and shaped using standard endodontic procedures and the tips sealed with cyanoacrylate cement. The root canal space was filled with an aqueous solution of 1.0 M gallium nitrate chelated with 1.0 M sodium citrate buffer (pH 7.2). The roots were then sectioned longitudinally into two equal halves. Each half was fixed to a translation stage that moved at a constant rate beneath a frequency-quadrupled Nd-YAG laser (266 nm) laser that was used to sample the concentration of 43Ca, 69Ga, and 71Ga by laser ablation across the thickness of root dentin to the periodontal surface. The plume of ablated dentin was swept into an inductively heated plasma chamber by argon gas and hence into a mass spectrometer. RESULTS: Quantitative analyses of the distribution of gallium showed it was highest adjacent to the root canal space and fell as more peripheral sites were sampled but then rose slightly at the external boundary of the root which is covered with a thin layer of atubular cementum. CONCLUSIONS: Even the lowest concentrations of gallium found in peripheral root dentin exceeded the 10(-4) M concentration required to inhibit osteoclastic activity. This simple endodontic treatment should undergo clinical trials to determine its efficacy in vivo. The laser ablation, inductively coupled mass spectrometry method is a powerful analytic tool for measuring spatial distribution of materials in mineralized tissues.

Dental Pulp Cavity↗

PubMed2004

Nitrogen- and storage-affected carbohydrate partitioning in high-light-adapted Pelargonium cuttings in relation to survival and adventitious root formation under low light.

BACKGROUND AND AIMS: The aim of this study was to determine the role of nitrogen- and storage-affected carbohydrate availability in rooting of pelargonium cuttings, focusing on the environmental conditions of stock plant cultivation at low latitudes, transport of cuttings, and rooting under the low light that prevails during the winter rooting period in Central European greenhouses. METHODS: Carbohydrate partitioning in high-light-adapted cuttings of the cultivar 'Isabell' was studied in relation to survival and adventitious root formation under low light. Effects of a graduated supply of mineral nitrogen to stock plants and of cutting storage were examined. KEY RESULTS: Nitrogen deficiency raised starch levels in excised cuttings, whereas the concentrations of glucose and total sugars in leaves and the basal stem were positively correlated with internal total nitrogen (Nt). Storage reduced starch to trace levels in all leaves, but sugar levels were only reduced in tissues of non-nitrogen deficient cuttings. Sugars accumulated in the leaf lamina of stored cuttings during the rooting period, whereas carbohydrates were simultaneously exhausted in all other cutting parts including the petioles, thereby promoting leaf senescence. The positive correlation between initial Nt and root number disappeared after storage. Irrespectively of storage, higher pre-rooting leaf glucose promoted subsequent sugar accumulation in the basal stem and final root number. The positive relationships between initial sugar levels in the stems with cutting survival and in leaves with root formation under low light were confirmed in a sample survey with 21 cultivars provided from different sources at low latitudes. CONCLUSIONS: The results indicate that adventitious rooting of pelargonium cuttings can be limited by the initial amount of nitrogen reserves. However, this relationship reveals only small plasticity and is superimposed by a predominant effect of carbohydrate availability that depends on the initial leaf sugar levels, when high-light adaptation and low current light conditions impair net carbon assimilation.

Adaptation, Physiological↗

PubMed2004

Assessment of inequality of root hair density in Arabidopsis thaliana using the Gini coefficient: a close look at the effect of phosphorus and its interaction with ethylene.

BACKGROUND AND AIMS: Root hair density (i.e. the number of root hairs per unit root length) in Arabidopsis thaliana varies among individual plants in response to different nutrient stresses. The degree of such variation, defined as inequality, serves as a unique indicator of the uniformity of response within a plant population to nutrient availability. METHODS: Using the Gini coefficient (G) as an inequality index, the inequality of root hair density in Arabidopsis thaliana 'Columbia' was evaluated under conditions of nutrient stresses; in particular the effect of phosphorus and its interaction with ethylene. KEY RESULTS: With decreasing phosphorus concentration, root hair density increased while inequality decreased logarithmically. The addition of the ethylene precursor 1-aminocyclopropane-1-carboxylate (ACC) under high phosphorus increased root hair density and decreased inequality by 7-fold. Inhibition of ethylene action with 1-methylcyclopropene (MCP) and silver thiosulphate (STS) under low phosphorus decreased root hair density, and increased inequality by 9-fold and 4-fold, respectively. The ethylene action inhibitors had little effect on root hair density under high phosphorus, but inequality increased 3-fold in the presence of MCP and decreased 2-fold in the presence of STS. Compared with the control, deficiencies in S, N and K increased inequality of root hair density, whereas deficiencies in P, Ca, B, Mn, Fe, Zn, Cu and Mg decreased inequality. In particular, the inequality of root hair density increased by over 2-fold under deficiencies of N or K, but decreased 14-fold under phosphorus deficiency. CONCLUSIONS: The inequality analysis indicates a strong correlation between prevalent signals from the environment (i.e. phosphorus stress) and the response of the plant, and the role of ethylene in this response. As the environmental signals become stronger, an increasing proportion of individuals respond, resulting in a decrease in variation in responsiveness among individual plants as indicated by reduced inequality.

Amino Acids, Cyclic↗

PubMed2005

Co-ordinated growth between aerial and root systems in young apple plants issued from in vitro culture.

BACKGROUND AND AIMS: In several species exhibiting a rhythmic aerial growth, the existence of an alternation between root and shoot growth has been demonstrated. The present study aims to investigate the respective involvement of the emergence of new organs and their elongation in relation to this phenomenon and its possible genotypic variation in young apple plants. METHODS: Two apple varieties, X6407 (recently named 'Ariane') and X3305 ('Chantecler' x 'Baujade'), were compared. Five plants per variety, issued from in vitro culture, were observed in minirhizotrons over 4 months. For each plant, root emergence and growth were observed twice per week. Growth rates were calculated for all roots with more than two segments and the branching density was calculated on primary roots. On the aerial part, the number of leaves, leaf area and total shoot length were observed weekly. KEY RESULTS: No significant difference was observed between varieties in any of the final characteristics of aerial growth. Increase in leaf area and shoot length exhibited a 3-week rhythm in X3305 while a weaker signal was observed in Ariane. The primary root growth rate was homogeneous between the plants and likewise between the varieties, while their branching density differed significantly. Secondary roots emerged rhythmically, with a 3-week and a 2-week rhythm, respectively, in X3305 and 'Ariane'. Despite a high intra-variety variability, significant differences were observed between varieties in the secondary root life span and mean length. A synchronism between leaf emergence and primary root growth was highlighted in both varieties, while an opposition phase was observed between leaf area increments and secondary root emergence in X3305 only. CONCLUSION: A biological model of dynamics that summarizes the interactions between processes and includes the assumption of a feedback effect of lateral root emergence on leaf emergence is proposed.

Cells, Cultured↗