[The ventral root afferent fibers and their physiological function].
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Afferent Pathways↗
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Complex physiological and molecular processes underlying root gravitropism.
Gravitropism allows plant organs to guide their growth in relation to the gravity vector. For most roots, this response to gravity allows downward growth into soil where water and nutrients are available for plant growth and development. The primary site for gravity sensing in roots includes the root cap and appears to involve the sedimentation of amyloplasts within the columella cells. This process triggers a signal transduction pathway that promotes both an acidification of the wall around the columella cells, an alkalinization of the columella cytoplasm, and the development of a lateral polarity across the root cap that allows for the establishment of a lateral auxin gradient. This gradient is then transmitted to the elongation zones where it triggers a differential cellular elongation on opposite flanks of the central elongation zone, responsible for part of the gravitropic curvature. Recent findings also suggest the involvement of a secondary site/mechanism of gravity sensing for gravitropism in roots, and the possibility that the early phases of graviresponse, which involve differential elongation on opposite flanks of the distal elongation zone, might be independent of this auxin gradient. This review discusses our current understanding of the molecular and physiological mechanisms underlying these various phases of the gravitropic response in roots.
Gravitropism↗
Spinal roots of rats poisoned with methylmercury: physiology and pathology.
The evoked potentials in the ventral and dorsal roots were recorded independently by stimulating the sciatic nerve of both control and methylmercury-poisoned rats. Poisoned rats showed markedly decreased amplitudes but normal latencies of the potentials evoked in the dorsal roots. Potentials evoked in the ventral roots had normal latencies and amplitudes. Pathological correlates indicated acute axonal degeneration of the dorsal roots, with a significant decrease of the large and small myelinated fiber densities. The ventral roots were histologically unremarkable. Our pathological confirmation of the electrophysiologic changes in the methylmercury-poisoned rats enables us to substantially assess the pathophysiological aspects of acute lesions in the spinal roots.
Animals↗
The hemodynamic performance of standard bileaflet valves is impaired by a tilted implantation position.
OBJECTIVES: Severe sclerosis of the native aortic annulus can result in a tilted implantation position of mechanical prostheses. In this study, the effects of tilting and rotation on the hemodynamic performance of standard bileaflet valves were assessed in an extracorporeal mock circulatory system. METHODS: A pulsatile mock circulation driven by a Berlin Heart system was developed. Main physiological components of the human circulation were mimicked. SJM-AHPJ prostheses (21, 23, 25 mm) were mounted in an artificial aortic root containing physiologically oriented coronary ostia. All experiments were performed under constant conditions (stroke volume 60 ml, heart rate 70 bpm, systolic pressure 130 mmHg). Hydrostatic pressures were measured via fluid-filled catheters, transvalvular flow by ultrasonic probes. Data were digitally recorded at 50 Hz. Multiple pressure, volume, energy, and dimension parameters were derived off-line. Each valve was tested in a 0 degrees (untilted) versus 20 degrees (tilted) position at three axial rotation angles (0 degrees, 45 degrees, 90 degrees ). Tilting was performed independent of rotation by elevation of the prosthesis in the non-coronary sinus. RESULTS: In all valves and all rotation angles, tilting resulted in a size-dependent significant increase of mean pressure gradient (range, 28-35% [21 mm valve], 59-96% [23 mm valve], 124-220% [25 mm valve]), valvular resistance (39-51, 84-121, 177-332%), regurgitation volume (84-148, 32-131, 93-118%), and systolic energy loss (113-146, 30-132, 69-213%), as well as a decrease of total stroke volume (2-5, 0-11, 3-10%), effective stroke volume (6-11, 9-14, 14-22%), cardiac output (6-11, 8-14, 13-22%), and effective opening area (16-24, 32-37, 47-57%). The strongest impairment of hemodynamic performance was seen at 90 degrees rotation with reference to total and effective stroke volume, cardiac output, mean pressure gradient, and regurgitation fraction. CONCLUSIONS: Tilting of bileaflet valves resulted in a significant impairment of systolic and diastolic hemodynamics. Superiority of larger valves diminished in the tilted position. The strongest tilting effect was seen at 90 degrees rotation. Such a position should therefore be avoided or surgically corrected by rotating the valve.
Aortic Valve↗
Studies on the physiology of hyacinth bulbs VII. Root and bulblet-like regenerations from the ovary wall of Hyacinthus orientalis L.
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Plant Growth Regulators↗
Heterogeneity in spatial P-distribution and foraging capability by Zea mays: effects of patch size and barriers to restrict root proliferation within a patch.
BACKGROUND AND AIMS: Localized proliferation of roots in nutrient-enriched patches seems to be an adaptive response in many plants, but its function is still debatable. To understand the efficiency and limitation of foraging behaviour, the impact of patch size and the presence or absence of a barrier to root proliferation within phosphorus (P)-enriched patches was examined. METHODS: In pots filled with P-poor soil, six treatments of heterogeneous P supply were prepared: three patch sizes with or without a root barrier between patches. In addition, a homogeneous P supply treatment was also prepared. Irrespective of these treatments, each pot received the same total amount of P. Maize (Zea mays) was grown in each pot for 45 d in a greenhouse. KEY RESULTS: P content and biomass were greatest in plants grown in the largest patch due to successful root proliferation, and were higher in the presence of a root barrier. Interestingly, plants preferentially developed adventitious nodal roots projecting from the stem into the P-enriched soil, particularly in the largest patch with a root barrier. Removal of the barrier reduced the P-uptake capacity per unit root surface area or volume in P-enriched patches, revealing that the P-uptake capacity per root can be suppressed even in P-rich soil if other portions on the root axis encounter P-poor conditions. CONCLUSIONS: The results suggest that the efficiency of root morphological plasticity is largely determined by the size of the P-enriched patch. Furthermore, the results imply a novel aspect of P-uptake physiology that roots in heterogeneous P cannot demonstrate their potential capacity, as would be observed in roots encountering P continuously; this effect is probably mediated by an internal root factor.
Nitrogen↗
Pathoanatomy and pathophysiology of nerve root compression.
The anatomy and physiology of the nerve root complex in the lumbar spine are reviewed, with special reference to the effects of mechanical deformation of nerve roots in association with intervertebral disc herniation and spinal stenosis. Biomechanical aspects of nerve root deformation induced by compression are discussed. The functional changes induced by compression can be caused by mechanical nerve fiber deformation but also may be a consequence of changes in nerve root microcirculation, leading to ischemia and formation of intraneural edema. Nerve root compression can, by different neurophysiologic mechanisms, induce motor weakness and altered sensibility or pain. Intraneural edema and demyelination seem to be critical factors for the production of pain in association with nerve root compression.
Capillary Permeability↗
Root growth maintenance during water deficits: physiology to functional genomics.
Progress in understanding the network of mechanisms involved in maize primary root growth maintenance under water deficits is reviewed. These include the adjustment of growth zone dimensions, turgor maintenance by osmotic adjustment, and enhanced cell wall loosening. The role of the hormone abscisic acid (ABA) in maintaining root growth under water deficits is also addressed. The research has taken advantage of kinematic analysis, i.e. characterization of spatial and temporal patterns of cell expansion within the root growth zone. This approach revealed different growth responses to water deficits and ABA deficiency in distinct regions of the root tip. In the apical 3 mm region, elongation is maintained at well-watered rates under severe water deficit, although only in ABA-sufficient roots, whereas the region from 3-7 mm from the apex exhibits maximum elongation in well-watered roots, but progressive inhibition of elongation in roots under water deficit. This knowledge has greatly facilitated discovery of the mechanisms involved in regulating the responses. The spatial resolution with which this system has been characterized and the physiological knowledge gained to date provide a unique and powerful underpinning for functional genomics studies. Characterization of water deficit-induced changes in transcript populations and cell wall protein profiles within the growth zone of the maize primary root is in progress. Initial results from EST and unigene analyses in the tips of well-watered and water-stressed roots highlight the strength of the kinematic approach to transcript profiling.
Adaptation, Physiological↗
Calcium hydroxide as a root canal filling material in primary teeth--a pilot study.
A pilot study was carried out in five mandibular primary molars using calcium hydroxide (Ca(OH)2) Paste as root canal filling material to find out an alternative to the routinely used zinc oxide eugenol (ZnOE), which is non-resorbable and causes deflection of succedaneous teeth. The six month clinical and radiographic follow-up carried out at 2 months interval, revealed that the treated teeth with Ca(OH)2 as root canal filling material were successful, showing no pain and tenderness to percussion. A tendency for decrease in size of radiolucency was seen. Two teeth showed complete healing of the periradicular radiolucency. Depletion of Ca(OH)2 paste was seen from the root canals even prior to physiological resorption of roots in 2 out of 5 treated teeth.
Calcium Hydroxide↗
Competition- and resource-mediated tradeoffs between growth and defensive chemistry in trembling aspen (Populus tremuloides).
Costs of defense are thought to maintain genetic variations in the expression of defense within plant populations. As with many plant species, aspen exhibits considerable variation in allocation to secondary metabolites. This study examined the independent and interactive effects of genotype, soil fertility and belowground competition on defensive chemistry and growth in trembling aspen (Populus tremuloides). Four aspen genotypes were grown with high and low soil fertility, and with and without root competition. Physiological, morphological and allocational determinants of growth were measured to identify growth-defense tradeoffs. Nutrient limitation and competition decreased growth, leaf mass ratio, leaf nitrogen concentration and photosynthesis, and increased root : shoot ratio and leaf condensed tannin concentrations. The competition treatment also resulted in increased leaf phenolic glycoside (PG) concentrations. Aspen growth was negatively correlated with PG concentrations under low fertility with competition. The relationship between growth and its major determinants was also negatively related to foliar condensed tannins expressed as a proportion of tree mass, indicating an additional indirect cost of allocation to secondary metabolites.
Biomass↗
Atypical morphology of dark septate fungal root endophytes of Bouteloua in arid southwestern USA rangelands.
Native grasses of semi-arid rangelands of the southwestern USA are more extensively colonized by dark septate endophytes (DSE) than by traditional mycorrhizal fungi. Roots of dominant grasses ( Bouteloua sp.) native to arid southwestern USA rangelands were prepared and stained using stains specific for fungi (trypan blue) and for lipids (sudan IV). This revealed extensive internal colonization of physiologically active roots by atypical fungal structures that appear to function as protoplasts, without a distinguishable wall or with very thin hyaline walls that escape detection by methods staining specifically for fungal chitin. These structures were presumed to be active fungal stages that progressed to form stained or melanized septate hyphae and microsclerotia characteristic of DSE fungi within dormant roots. The most conspicuous characteristic of these fungi were the unique associations that formed within sieve elements and the accumulation of massive quantities of lipids. This interface suggests a biologically significant location for carbon transfer between the plant and fungus. The continuous intimate association with all sieve elements, cortical and epidermal cells as well as external extension on the root surface and into the soil indicates that they are systemic and considerably more prevalent than previously thought. A fungal network associated with a mucilaginous complex observed on the root surface and its potential role in root function in dry soil is discussed. It is suggested that those fungi that non-pathogenically and totally colonize plant cells be classed as systemic endophytic fungi (SEF). This would refine the broad designation of DSE fungi. The potential mutualistic benefit of SEF for native plants in arid ecosystems based on the extent of lipid accumulation and its apparent distribution is discussed.
Desert Climate↗
Physiological, morphological and allocational plasticity in understory deciduous trees: importance of plant size and light availability.
In a 4-year study, we investigated changes in leaf physiology, crown morphology and whole-tree biomass allocation in seedlings and saplings of shade-tolerant sugar maple (Acer saccharum Marsh.) and intermediate shade-tolerant yellow birch (Betula alleghaniensis Britt.) growing in natural understory light (0.5 to 35% of full sunlight) or in understory light reduced by 50% with shade nets to simulate the effect of gap closure. Leaf physiological parameters were mainly influenced by the light gradient, whereas crown morphological and whole-tree allocational parameters were mainly influenced by tree size. No single physiological, morphological or allocational trait was identified that could explain the difference in shade tolerance between the species. Yellow birch had higher growth rates, biomass allocation to branches and leaf physiological plasticity and lower crown morphological plasticity in unmodified understory light than sugar maple. Sugar maple did not display significant physiological plasticity, but showed variation with tree size in both crown morphology and whole-tree biomass allocation. When sugar maple was small, a greater proportion of whole-tree biomass was allocated to roots. However, physiological differences between the species decreased with decreasing light and most morphological and allocational differences tended to disappear with increasing tree size, suggesting that many species differences in shade-tolerance are expressed mainly during the seedling stage. Understory trees of both species survived for 4 years under shade nets, possibly because of higher plasticity when small and the use of stored reserves when taller.
Acer↗
Functional recovery after ventral root avulsion and implantation in the spinal cord.
This survey describes experiments performed in rats, cats and monkeys aiming at the management of motor deficits after ventral root rupture or avulsion from the spinal cord as seen in brachial plexus lesions. After intramedullary implantation of the ruptured or avulsed ventral root, neurophysiological data show that alpha and probably also gamma motoneurons are capable of producing new axons which regrow for a considerable distance in the spinal cord before entering the implanted root. Intracellular physiological experiments demonstrate that new axons can conduct action potentials and elicit muscle responses. The neurons are reconnected in segmental spinal cord activity and respond to impulses in sensory fibres. In primates, implantation of avulsed ventral roots in the brachial plexus resulted in functional restitution. It is concluded that intraspinal implantation of avulsed ventral roots significantly promotes motor recovery in the muscles supplied by the lesioned spinal cord segments. These studies indicate the possibility of surgical treatment of ventral root avulsion injuries in brachial plexus lesions in man.
Animals↗
Three-dimensional numeric simulation of flow through an aortic bileaflet valve in a realistic model of aortic root.
A three-dimensional, realistic model of an aortic mechanical heart valve and Valsalva sinuses was developed to predict, by means of a numerical time dependent simulation, the flow field during a fraction of the systolic period. The numeric simulation was performed upon a model of valve similar to a Carbomedics 27 mm placed in a physiologic aortic root shaped model, in which no symmetry planes were exploited to reach a more realistic level. Input data for the simulation have been acquired during an experimental session on the same valve, according to the guidelines of testing protocol for prosthetic heart valves. Flow was assumed to be Newtonian and laminar at low regime and the leaflets fixed in the fully open position. The forward flow of the systolic phase was investigated, and a comparison with experimental results was performed at peak systole, the most representative point of the cardiac cycle. The results of this simulation furnished a reasonable indication (in terms of fluid dynamics) parameters downstream of the prosthetic device, especially in Valsalva sinuses, the role of which is proven to affect the valve's performance.
Aortic Valve↗
Regulation of high-affinity sulphate transporters in plants: towards systematic analysis of sulphur signalling and regulation.
Plants require the function of plasma membrane-bound sulphate transporters for the initial uptake of inorganic sulphate. Part of this fundamental process is the energy-dependent proton/sulphate co-transport systems that are located in the surface cell layers of roots. During sulphur limitation, plants are able to activate the expression of sulphate transporters that facilitate the uptake of sulphate in roots. SULTR1;1 and SULTR1;2 are suggested to be the essential components of the sulphate uptake system in Arabidopsis roots. The physiological importance of SULTR1;1 and SULTR1;2 is supported by characteristics that can cope with sulphur deficiency: they were (i) functional high-affinity sulphate transporters; (ii) induced by sulphur limitation at the mRNA levels; and (iii) predominantly localized in the root hairs, epidermis, and cortex. The expression of high-affinity sulphate transporters was primarily regulated by sulphur in a promoter-dependent manner. Aside from the sulphur-specific regulation, the induction of SULTR1;1 and SULTR1;2 high-affinity sulphate transporters by sulphur limitation was dependent on the supply of carbon and nitrogen. In this review, the application of SULTR promoter-GFP systems for the analysis of regulatory pathways of sulphate acquisition in plants is described.
Anion Transport Proteins↗
Monitoring pulp vitality after transplantation of teeth with mature roots: a case report.
AIM: To initiate discussion on the value of routine root canal treatment for transplanted teeth. SUMMARY: Autotransplantation is an accepted treatment option to replace missing teeth. It is generally considered that revascularization of the pulp following such a procedure is more favourable in teeth with immature roots. In teeth with closed apices root canal treatment is considered necessary. This paper presents a case of pulp revascularization in a transplanted tooth with mature roots and casts doubt on whether root canal treatment is essential in such situations. An alternative treatment protocol is proposed. KEY LEARNING POINTS: * Following transplantation original pulp tissue may survive the operation. * Teeth with obliterated pulp space do not become necrotic more often than those without obliteration. * Monitoring the tooth is an acceptable alternative to automatic root canal treatment for transplanted teeth. * Root canal treatment should be undertaken only upon occurrence of pathological signs.
Adolescent↗
Site-specific expression of mRNAs for osteonectin, osteocalcin, and osteopontin revealed by in situ hybridization in rat periodontal ligament during physiological tooth movement.
We investigated the gene expression for non-collagenous proteins in periodontal ligament (PDL) by in situ hybridization histochemistry with a non-radioisotopic probe with cRNAs for osteocalcin (Osc), osteonectin (Osn), and osteopontin (Opn) in rat maxillary dento-alveolar unit containing molars and intact PDL. A highly intense positive signal for Osn and Osc mRNAs was expressed at all distal surfaces of the interradicular septum of buccal roots of the upper second molar in 7-week-old Sprague-Dawley male rats. Cells showing positive signals for Osn and Osc mRNAs were osteoblasts and osteoprogenitor cells. The distribution of Opn mRNA-positive signal was demonstrable at the mesial surface of the interradicular septum of buccal roots, where physiological bone resorption was specifically restricted during physiological tooth movement. Opn mRNA was expressed in cells on the bone resorption surface, including osteoclasts, and osteocytes. A moderately intense positive signal for Osn mRNA was distributed in fibroblasts throughout the ligament. Odontoblasts and pre-mature odontoblasts exhibited a strong signal for Osn and Osc mRNA. Cementoblasts and cementocytes were positive for Osn, Osc, and Opn mRNAs. These findings suggest physiological roles of Osc, Osn, and Opn in bone remodeling, PDL remodeling, dentinogenesis, and cementogenesis.
Animals↗
Growth and physiological responses of neotropical mangrove seedlings to root zone hypoxia.
Seedlings of Rhizophora mangle L., Avicennia germinans (L.) Stearn., and Laguncularia racemosa (L.) Gaertn. f. were cultured in aerated or N(2)-purged solution for 12 weeks to assess their relative responses to low oxygen tensions. All three species responded to low oxygen treatment by modifying physiological and morphological patterns to decrease carbon loss by root respiration. However, the extent to which seedling physiology and morphology were altered by low oxygen treatment differed among species. Maintenance of root oxygen concentrations, root respiration rates and root extension rates by R. mangle demonstrated an ability to avoid low oxygen stress with minimal changes in root morphology and physiology. In contrast, oxygen concentrations in A. germinans and L. racemosa roots declined from 16 to 5% or lower within 6 h of treatment. Root hypoxia led to significant decreases in respiration rates of intact root systems (31 and 53% below controls) and root extension rates (38 and 76% below controls) by A. germinans and L. racemosa, respectively, indicating a greater vulnerability of these species to low oxygen tensions in the root zone compared with R. mangle. I conclude that the relative performance of mangrove seedlings growing in anaerobic soils is influenced by interspecific differences in root aeration and concomitant effects on root morphology and physiology.
Journal Article↗