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At least 271 records · Page 15Linked to original sources
PubMed1999

Dental root resorption.

This article presents a review of physiologic mechanisms involved in various types of root resorption that may be encountered clinically. Included is a brief overview of suggested homeostatic mechanisms of the periodontal ligament and the role of the intermediate cementum in inhibiting root resorption. Root resorption (surface, inflammatory, and replacement) associated with traumatic injuries is discussed, with emphasis on etiology and the ability to provide treatment. The final discussion relates to other types of resorption, based on a classification of internal, cervical, and external resorption associated with periradicular pathosis and resulting from pressure in the periodontal ligament.

Humans↗
PubMed1984

Metabolic response of river birch and European birch and European birch roots to hypoxia.

Flood tolerance of woody plants has been attributed to internal oxygen diffusion from shoot to root, metabolic adaptation within the root, or both. The purpose of this study was to compare several biochemical and physiological responses of birch roots to hypoxia in order to determine the nature of root metabolic adaptation to low oxygen tension. One-year-old seedlings of flood-tolerant river birch (Betula nigra L.) and flood-intolerant European birch (Betula pendula Roth) were transferred to solution culture, and the solutions were bubbled with air or nitrogen. After 18 days of hypoxia, total adenosine phosphate and ATP contents of river birch roots were 35% and 23% of controls, respectively, whereas those of European birch roots were 13% and 8%. Adenylate energy charge of river birch roots decreased between 6 and 12 days of hypoxia. In contrast, energy charge of European birch roots decreased after only 1 day of hypoxia. In vitro activity of cytochrome c oxidase and oxygen consumption capacity of excised roots from both birch species decreased under hypoxia. In vitro activity of alcohol dehydrogenase from roots of both species increased after 1 day of hypoxia. However, alcohol dehydrogenase activity from river birch roots increased 25-fold after 6 days of hypoxia, whereas that from European birch decreased back to control levels. Hypoxia decreased malate content of roots from both species. Metabolic adaptation within the root, rather than internal oxygen diffusion, appears to be responsible for the relative tolerance of river birch to hypoxia.

Journal Article↗
PubMed2002

The physiology and biophysics of an aluminum tolerance mechanism based on root citrate exudation in maize.

Al-induced release of Al-chelating ligands (primarily organic acids) into the rhizosphere from the root apex has been identified as a major Al tolerance mechanism in a number of plant species. In the present study, we conducted physiological investigations to study the spatial and temporal characteristics of Al-activated root organic acid exudation, as well as changes in root organic acid content and Al accumulation, in an Al-tolerant maize (Zea mays) single cross (SLP 181/71 x Cateto Colombia 96/71). These investigations were integrated with biophysical studies using the patch-clamp technique to examine Al-activated anion channel activity in protoplasts isolated from different regions of the maize root. Exposure to Al nearly instantaneously activated a concentration-dependent citrate release, which saturated at rates close to 0.5 nmol citrate h(-1) root(-1), with the half-maximal rates of citrate release occurring at about 20 microM Al(3+) activity. Comparison of citrate exudation rates between decapped and capped roots indicated the root cap does not play a major role in perceiving the Al signal or in the exudation process. Spatial analysis indicated that the predominant citrate exudation is not confined to the root apex, but could be found as far as 5 cm beyond the root cap, involving cortex and stelar cells. Patch clamp recordings obtained in whole-cell and outside-out patches confirmed the presence of an Al-inducible plasma membrane anion channel in protoplasts isolated from stelar or cortical tissues. The unitary conductance of this channel was 23 to 55 pS. Our results suggest that this transporter mediates the Al-induced citrate release observed in the intact tissue. In addition to the rapid Al activation of citrate release, a slower, Al-inducible increase in root citrate content was also observed. These findings led us to speculate that in addition to the Al exclusion mechanism based on root citrate exudation, a second internal Al tolerance mechanism may be operating based on Al-inducible changes in organic acid synthesis and compartmentation. We discuss our findings in terms of recent genetic studies of Al tolerance in maize, which suggest that Al tolerance in maize is a complex trait.

Adaptation, Physiological↗
PubMed1998

Auxin and ethylene promote root hair elongation in Arabidopsis.

Genetic and physiological studies implicate the phytohormones auxin and ethylene in root hair development. To learn more about the role of these compounds, we have examined the root hair phenotype of a number of auxin- and ethylene-related mutants. In a previous study, Masucci and Schiefelbein (1996) showed that neither the auxin response mutations aux1 and axr1 nor the ethylene response mutations etr1 and ein2 have a significant effect on root hair initiation. In this study, we found that mutants deficient in either auxin or ethylene response have a pronounced effect on root hair length. Treatment of wild-type, axr1 and etr1 seedlings with the synthetic auxin, 2,4-D, or the ethylene precursor ACC, led to the development of longer root hairs than untreated seedlings. Furthermore, axr1 seedlings grown in the presence of ACC produce ectopic root hairs and an unusual pattern of long root hairs followed by regions that completely lack root hairs. These studies indicate that both auxin and ethylene are required for normal root hair elongation.

2,4-Dichlorophenoxyacetic Acid↗
PubMed1985

An electron transport system in maize roots for reactions of glutamate synthase and nitrite reductase : physiological and immunochemical properties of the electron carrier and pyridine nucleotide reductase.

A non-heme iron containing protein which bears an antigenic similarity to ferredoxin from spinach leaves (Spinacia oleracea L.) has been identified in extracts prepared from young roots of maize (Zea mays L., hybrid W64A x W182E). The ferredoxin-like root electron carrier could substitute for ferredoxin in a cytochrome c reduction system in which pyridine nucleotide (NADPH) reduces the root electron carrier in a reaction catalyzed by ferredoxin-NADP(+) reductase (EC 1.6.7.1) from spinach leaves. However, the root electron carrier did not mediate the photoreduction of NADP(+) in an illuminated reconstituted chloroplast system.A pyridine nucleotide reductase which shares identical immunological determinants with the ferredoxin-NADP(+) reductase from spinach leaves has also been characterized from maize roots. Root pyridine nucleotide reductase mediated the transfer of electrons from either NADPH or NADH to cytochrome c via ferredoxin or the root electron carrier. Under chemical reducing conditions with sodium dithionite and bicarbonate, the ferredoxin-like root electron carrier served as an electron carrier for the ferredoxin-requiring glutamate synthase (EC 1.4.7.1) and nitrite reductase (EC 1.7.7.1) obtained from maize roots or leaves. In the presence of root pyridine nucleotide reductase and root electron carrier, either NADPH or NADH served as the primary electron donor for glutamate synthesis in extracts from maize roots or leaves. The electron transport system originating with NADH or NADPH, was, however, not able to mediate the reduction of NO(2) (-) to NH(3).

Journal Article↗
PubMed2002

A possible stress physiological role of abscisic acid conjugates in root-to-shoot signalling.

Abscisic acid (ABA) conjugates, predominantly their glucose esters, have recently been shown to occur in the xylem sap of different plants. Under stress conditions, their concentration can rise substantially to levels that are higher than the concentration of free ABA. External ABA conjugates cannot penetrate apoplastic barriers in the root. They have to be hydrolysed by apoplastic enzymes in the root cortex. Liberated free ABA can then be redistributed to the root symplast and dragged directly across the endodermis to the stele. Endogenous ABA conjugates are formed in the cytosol of root cells, transported symplastically to the xylem parenchyma cells and released to the xylem vessels. The mechanism of release is unknown; it may include the action of ABC-transporters. Because of its extremely hydrophilic properties, ABA-GE is translocated in the xylem of the stem without any loss to the surrounding parenchyma. After arrival in the leaf apoplast, transporters for ABA-GE in the plasmalemma have to be postulated to redistribute the conjugates to the mesophyll cells. Additionally, apoplastic esterases can cleave the conjugate and release free ABA to the target cells and tissues. The activity of these esterases is increased when barley plants are subjected to salt stress.

Journal Article↗
PubMed1983

Clastogenic and physiological response of chromosomes to nine pesticides in the Vicia faba in vivo root tip assay system.

9 common pesticides were assayed for clastogenic and physiological activity using Vicia faba as a eukaryotic, whole-organism, test system. The compounds tested included the insecticides acephate, demeton, monocrotophos, parathion-methyl, and trichlorfon; the fungicides captan and folpet; and the herbicides bromacil and simazine. The chemicals have been grouped according to relative genotoxicity (strongly positive: demeton, parathion-methyl; positive: folpet, acephate, monocrotophos, captan; weakly positive: bromacil, trichlorfon, simazine). The results were compared with those reported from other assay systems.

Animals↗
PubMed1995

Cu2+ Reduction by Tomato Root Plasma Membrane Vesicles.

Reduction of Cu2+ by plasma membrane vesicles isolated from tomato (Lycopersicon esculentum Mill.) roots was investigated. Plants were grown in hydroponic culture with complete nutrition for 4 weeks or were deprived of Fe for the last 7 d. Plasma membrane vesicles were prepared by aqueous two-phase partitioning. Reduction of Cu, Fe, and ferricyanide by plasma membrane vesicles was measured. An increase in the activity of all three pyridine-nucleotide-dependent activities was noted in plasma membrane preparations from Fe-deficient, compared to Fe-sufficient, plants. Solubilization and chromatographic separation of two plasma membrane electron transport systems indicated that the Fe-chelate reductase was probably responsible for reduction of Cu. Assays used a variety of Cu chelates, and for each the Cu activity in the assay was determined by the program Geochem PC. The rate of reduction of Cu correlated with the level of Cu activity, and results support the idea that free Cu2+ and not Cu chelates may serve as the true substrate for reduction. Reduction was observed only in assays in which Cu activity was equivalent to Cu-enriched or Cu-toxic soils. These results suggest that reduction of Cu by tomato root may have little or no physiological relevance under conditions experienced by the root in the soil.

Journal Article↗
PubMed2005

Differential gene expression by Metarhizium anisopliae growing in root exudate and host (Manduca sexta) cuticle or hemolymph reveals mechanisms of physiological adaptation.

Like many other fungal pathogens Metarhizium anisopliae is a facultative saprophyte with both soil-dwelling and insect pathogenic life-stages. In addition, as M. anisopliae traverses the cuticle and enters the hemolymph it must adapt to several different host environments. In this study, we used expressed sequence tags and cDNA microarray analyses to demonstrate that physiological adaptation by M. anisopliae to insect cuticle, insect hemolymph, bean root exudate (a model for life in the soil), and nutrient rich Sabouraud dextrose broth (SDB) involves different subsets of genes. Overall, expression patterns in cuticle and hemolymph clustered separately from expression patterns in root exudates and SDB, indicative of critical differences in transcriptional control during pathogenic and saprophytic growth. However, there were differences in gene expression between hemolymph and cuticle and these mostly involved perception mechanisms, carbon metabolism, proteolysis, cell surface properties, and synthesis of toxic metabolites. These differences suggest previously unsuspected stratagems of fungal pathogenicity that can be tested experimentally. Examples include the switch-off of cuticle-degrading proteases and a dramatic cell wall reorganization during growth in hemolymph.

Adaptation, Physiological↗
PubMed2005

Quantitative determination of callose in tree roots.

The formation of callose in tree roots has been suggested as a physiological indicator of aluminum (Al) toxicity. Quantifying callose in the roots in forest soils, however, is hampered by the presence of autofluorescent materials in the roots that disturb the measurement of callose by fluorescence spectrophotometry. Tannins in the roots cause these measurement problems. Here we report on the measurement of callose in the root apices of European chestnut (Castanea sativa) seedlings collected in an acidified forest soil. The callose was quantified with a modified protocol which included three washing steps with polyvinylpolypyrrolidone (PVPP) before the callose was extracted. This procedure reduced the autofluorescence by about 50%. With the use of water or ethanol alone, callose could be measured in only about 15% of the root samples, whereas with the use of PVPP callose could be determined in 95% of the samples. This improved method could help to evaluate the effects of Al toxicity on tree roots grown in forest soils, where callose is detected as a physiological indicator.

Fagaceae↗
PubMed1996

Gravisensitivity of cress roots: investigations of threshold values under specific conditions of sensor physiology in microgravity.

The minimum dose (dose = stimulus x time), one of three threshold values related to gravity, was determined under microgravity conditions for cress roots. Seedlings were cultivated on a 1g centrifuge in orbit and under microgravity, respectively. After continuous stimulation on a threshold centrifuge, minimum doses of 20-30 gs for microgravity roots and 50-60 gs for roots grown on a 1g centrifuge were estimated, which indicated that microgravity roots have a higher sensitivity than 1g roots. These results do not confirm the threshold value of 12gs which was determined for cress roots using the slow rotating clinostat. Following application of intermittent stimuli to microgravity-grown roots, gravitropic responses were observed after two stimuli of 13.5 gs separated by a stimulus-free interval of 118s. Generally, this demonstrates that higher plants are able to 'sum up' stimuli which are below the threshold value. Microscopic investigations of the cellular structure corresponding to stimulations in the range of the threshold value demonstrated a small displacement of statoliths in root statocytes. No significant correlation was observed between gravitropic curvature and statolith displacement. If the statolith theory is accepted, it can be concluded that stimulus transformation must occur in the cytoplasm in the near vicinity of the statoliths and that this transformation system--probably involving cytoskeletal elements--must have been affected during microgravity seedling cultivation.

Centrifugation↗
PubMed2005

Mechanical properties of spinal nerve roots subjected to tension at different strain rates.

An understanding of the biomechanical and physiological properties of spinal nerve roots, particularly in response to tension, is critical in understanding the pathomechanisms of pain and nerve root injury and subsequent management of related injuries. Biomechanical properties of dorsal nerve roots at the lumbar and sacral levels were evaluated at various strain rates. Nerve roots were stretched at two different rates, 0.01 mm/s (Group A, quasistatic) and 15 mm/s (Group B, dynamic). Load, displacement and digital video data were obtained as the nerve roots were stretched until failure. Maximum stress, strain at maximum stress and modulus of elasticity (E) were calculated from the load-displacement measurements. Comparison of mechanical properties and failure patterns of nerve roots at two different rates revealed significant differences. Maximum load, maximum stress and E values of 5.7+/-2.7 gm, 257.9+/-111.3 kPa and 1.3+/-0.8 MPa were observed for Group A and 13.9+/-7.5 gm, 624.9+/-306.8 kPa and 2.9+/-1.5 MPa were observed for Group B, respectively. Higher maximum load, maximum stress and E values occurred at the dynamic stretch rate as compared to the quasistatic stretch rate, illustrating the strain-rate dependency of spinal nerve roots. No differences were observed in the strain values. Differences in mechanical behavior of nerve roots were also observed among the four root levels (L4-S1). A significant interaction effect was observed between nerve root diameter and stretch rates. Overall, results from the present study demonstrate viscoelastic material properties of spinal nerve roots and provide better insight on the tensile properties of nerve roots at different strain rates.

Animals↗
PubMed2003

Physiological, biochemical and molecular analysis of sugar-starvation responses in tomato roots.

Two-month-old tomato plants were submitted to day/night cycles and to prolonged darkness in order to investigate the physiological and biochemical response to sugar starvation in sink organs. Roots appeared particularly sensitive to the cessation of photosynthesis, as revealed by the reduction of the growth rate and the decline of the carbohydrate and protein content. Therefore, excised tomato roots were used as a model to deepen the characterization of sugar starvation symptoms. In excised roots, the endogenous sugars were rapidly exhausted and significant degradation of protein was observed. Glutamine and asparagine accounted for most of the nitrogen released by protein breakdown. Respiration declined and proliferation- and growth-associated genes were repressed soon after the beginning of the sugar depletion. Among the genes studied, only the gene encoding asparagine synthetase was strongly induced. All the starvation symptoms were reversible when the roots were resupplied with sugar. When the culture conditions deteriorated, the metabolic and molecular changes led to the triggering of apoptosis of the root cells.

Amino Acids↗
PubMed2004

A proteomic analysis identifies glutathione S-transferase isoforms whose abundance is differentially regulated by ethylene during the formation of early root epidermis in Arabidopsis seedlings.

The plant hormone ethylene has been shown to play an important role in root hair development in Arabidopsis. With the aid of proteomic analysis, we identified three distinct glutathione S-transferase (GST) isoforms, AtGSTF2, AtGSTF8, and AtGSTU19, expressed early in root epidermal establishment in Arabidopsis seedlings. The AtGSTF2 protein was specifically up-regulated by ethylene. A subsequent RNA expression study revealed that the AtGSTF2 gene was highly sensitive to ethylene, whereas the transcripts for AtGSTF8 and AtGSTU19 were constitutively present in new root tissue of 4-day-old seedlings. The steady-state level of AtGSTF2 mRNA was greatly reduced in the roots of ethylene-insensitive mutants, while mutation at the CTR1 locus, which confers an ectopic root hair phenotype, resulted in a markedly elevated level of AtGSTF2 transcript in young root tissue. Although the physiological function of ethylene-induced AtGSTF2 is not yet clear, there are several possibilities for its role during early root development.

Amino Acids, Cyclic↗