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At least 109 records · Page 6Linked to original sources
PubMed1999

Stress-induced legume root nodule senescence. Physiological, biochemical, and structural alterations.

Nitrate-fed and dark-stressed bean (Phaseolus vulgaris) and pea (Pisum sativum) plants were used to study nodule senescence. In bean, 1 d of nitrate treatment caused a partially reversible decline in nitrogenase activity and an increase in O(2) diffusion resistance, but minimal changes in carbon metabolites, antioxidants, and other biochemical parameters, indicating that the initial decrease in nitrogenase activity was due to O(2) limitation. In pea, 1 d of dark treatment led to a 96% decline in nitrogenase activity and sucrose, indicating sugar deprivation as the primary cause of activity loss. In later stages of senescence (4 d of nitrate or 2-4 d of dark treatment), nodules showed accumulation of oxidized proteins and general ultrastructural deterioration. The major thiol tripeptides of untreated nodules were homoglutathione (72%) in bean and glutathione (89%) in pea. These predominant thiols declined by approximately 93% after 4 d of nitrate or dark treatment, but the loss of thiol content can be only ascribed in part to limited synthesis by gamma-glutamylcysteinyl, homoglutathione, and glutathione synthetases. Ascorbate peroxidase was immunolocalized primarily in the infected and parenchyma (inner cortex) nodule cells, with large decreases in senescent tissue. Ferritin was almost undetectable in untreated bean nodules, but accumulated in the plastids and amyloplasts of uninfected interstitial and parenchyma cells following 2 or 4 d of nitrate treatment, probably as a response to oxidative stress.

Antioxidants↗
PubMed2002

Effect of lacZY-marking of the 2,4-diacetyl-phloroglucinol producing Pseudomonas fluorescens-strain 5-2/4 on its physiological performance and root colonization ability.

Transgenic Pseudomonas fluorescens 5-2/4 with reinforced 2,4-diacetyl phloroglucinol (phl) production had shown increased biocontrol ability towards Pythium ultimum (Pu), but inferior root colonization ability compared to its wild type 5.014. Therefore, enhanced root colonization ability of the transgenic strain by repeated inoculation and reisolation on tomato plants was suggested. As a preparation for repeated inoculation and reisolation cycles, the construction of a negative control of the transgenic strain 5-2/4 by marking with lacZY and screening for a mutant possessing qualities comparable to 5-2/4 was performed. Morphologically, colonies of all of the 11 selected mutants were similar on MLXgal medium. The root colonization ability of two of the lacZY-marked strains (mutants 1 and 10) was comparable to the parental strain. These were also able to compete with the resident microflora of tomato seedlings to the same extent as the parental strain. Five mutants were excluded due to lower growth rates on Yeast Malt, King's B Medium (KB) and 0.1 Tryptic Soy Agar (mutant 4, 5 and 8), excessive growth and higher siderophore production on KB (mutant 10) and increased protease production (mutant 2). With respect to in vitro-antagonism of Pu, no differences could be found between the target strain and mutants 1, 3, 6, 7 and 9. Examination of sole carbon source utilization of these five lacZY-marked strains revealed a significantly higher utilization of alpha-D-lactose and lactulose compared to 5-2/4. However, significant differences could be found for 51% of the utilized carbon sources. Cluster analysis showed a high degree of similarity between 5-2/4 and mutant 1 both when analyzed with and without alpha-D-lactose. As mutant 1 also represented the colonization pattern most similar to the parental strain 5-2/4, it presents a presumptive subject for a negative control in the following inoculation and reisolation studies on tomato.

Carbon↗
PubMed1996

Physiological Characterization of Root Zn2+ Absorption and Translocation to Shoots in Zn Hyperaccumulator and Nonaccumulator Species of Thlaspi.

Radiotracer techniques were employed to characterize 65Zn2+ influx into the root symplasm and translocation to the shoot in Thlaspi caerulescens, a Zn hyperaccumulator, and Thlaspi arvense, a nonaccumulator. A protocol was developed that allowed us to quantify unidirectional 65Zn2+ influx across the root-cell plasma membrane (20 min of radioactive uptake followed by 15 min of desorption in a 100 [mu]M ZnCl2 + 5 mM CaCl2 solution). Concentration-dependent Zn2+ influx in both Thlaspi species yielded nonsaturating kinetic curves that could be resolved into linear and saturable components. The linear kinetic component was shown to be cell-wall-bound Zn2+ remaining in the root after desorption, and the saturable component was due to Zn2+ influx across the root-cell plasma membrane. This saturable component followed Michaelis-Menten kinetics, with similar apparent Michaelis constant values for T. caerulescens and T. arvense (8 and 6 [mu]M, respectively). However, the maximum initial velocity for Zn2+ influx in T. caerulescens root cells was 4.5-fold higher than for T. arvense, indicating that enhanced absorption into the root is one of the mechanisms involved in Zn hyperaccumulation. After 96 h 10-fold more 65Zn was translocated to the shoot of T. caerulescens compared with T. arvense. This indicates that transport sites other than entry into the root symplasm are also stimulated in T. caerulescens. We suggest that although increased root Zn2+ influx is a significant component, transport across the plasma membrane and tonoplast of leaf cells must also be critical sites for Zn hyperaccumulation in T. caerulescens.

Journal Article↗
PubMed1982

Physiology of Root-Associated Nitrogenase Activity in Oryza sativa.

An intact method for measuring immediately linear rates of acetylene reduction was used to investigate the relationship between temperature, pH, O(2) concentration, and light intensity with the rate of root-associated nitrogenase activity in rice (Oryza sativa L.). Nitrogenase activity varied over a temperature range of 10 to 50 degrees C and optimal rates of acetylene reduction were recorded at 35 degrees C. Nitrogenase activity was also influenced by the pH of the liquid surrounding the roots prior to assay. Maximal rates of acetylene reduction were recorded over a pH range from 5.8 to 7.5. Nitrogenase activity was significantly reduced by concentrations of O(2) 0.5% (v/v) or more when the intact plant assay method was used, and no optimum was detected. However, when the plant tops were removed and the cut ends sealed from the atmosphere for 4 hours, acetylene reduction rates were maximal at 0.25% O(2) (v/v). When plants were moved from sunlight (1,400 microeinsteins per square meter per second) to shade (9.6) root-associated nitrogenase activity at 35 degrees C significantly decreased 15 min later to one-fourth the rate and recovered upon return to sunlight. When the light intensity reaching the leaf canopy was progressively reduced from 1,050 to 54 microeinsteins per square meter per second the rate of root-associated nitrogenase activity decreased from 550 +/- 135 to 192 +/- 55 nanomoles ethylene per gram dry root per hour. The study suggests that the rate of root-associated nitrogenase activity in rice at constant temperature may well be mediated by variations in the concentration of O(2) resulting from changes in the rate of photosynthesis as well as variations in the rate of transport of photosynthate.

Journal Article↗
PubMed1980

[Titanium spray-layered human tooth root implantation under physiological stress].

Titanium-plasma-flame-spray coated endodontic stabilizers have been implanted in six patients after apicectomy. These endodontic stabilized teeth have been postoperatively under physiological stress. Histologically in one case there was six month post-operatively bone in direct contact to the implant surface and in certain areas the structure of a new periodontal membrane was formed.

Bone Regeneration↗
PubMed1990

Limitations of the use of plant material grown in Petri dishes for physiological experiments.

Roots of plants growing "aeroponically" (AP) on moistened filter paper in Petri dishes for a few days are fairly often used for physiological experiments (e.g. measurement of root growth), for ion or herbicide uptake tests, before the establishment of hydroponic or aseptic cultures although their hormonal status is markedly different from that of the hydroponic (HP) control. On the 4th day of germination the ethylene production of cucumber (Cucumis sativus L. cv. Budai csemege) roots growing in AP under controlled conditions increased considerably and exhibited a maximum curve, HP roots evolved ethylene much more constantly. The morphological changes in AP roots (e.g. inhibited elongation and swelling of primary roots, and increased formation of root hairs), resembling those caused by exogenously applied ethylene, can be prevented with 10(-5) M Ag+, an inhibitor of ethylene action. In roots of one-week-old AP seedlings, the amount of an acidic inhibitor, which as judged from the Rf values is likely to be abscisic acid (ABA), is about twice as high as in HP seedlings. An elevated ethylene or ABA level of AP roots may result in a reduced elongation of the primary roots. Counteraction of this inhibition by Ag+ suggests that the effect of ethylene is the primary event in the reduction of root length. When using plant material grown in Petri dishes the possibility of similar changes in hormonal status of the roots must be taken into consideration.

Abscisic Acid↗
PubMed2004

Controlled alternate partial root-zone irrigation: its physiological consequences and impact on water use efficiency.

Controlled alternate partial root-zone irrigation (CAPRI), also called partial root-zone drying (PRD) in other literature, is a new irrigation technique and may improve the water use efficiency of crop production without significant yield reduction. It involves part of the root system being exposed to drying soil while the remaining part is irrigated normally. The wetted and dried sides of the root system are alternated with a frequency according to soil drying rate and crop water requirement. The irrigation system is developed on the basis of two theoretical backgrounds. (i) Fully irrigated plants usually have widely opened stomata. A small narrowing of the stomatal opening may reduce water loss substantially with little effect on photosynthesis. (ii) Part of the root system in drying soil can respond to the drying by sending a root-sourced signal to the shoots where stomata may be inhibited so that water loss is reduced. In the field, however, the prediction that reduced stomatal opening may reduce water consumption may not materialize because stomatal control only constitutes part of the total transpirational resistance. The boundary resistance from the leaf surface to the outside of the canopy may be so substantial that reduction in stomatal conductance is small and may be partially compensated by the increase in leaf temperature. It is likely that densely populated field crops, such as wheat and maize, may have a different stomatal control over transpiration from that of fruit trees which are more sparsely separated. It was discussed how long the stomata can keep 'partially' closed when a prolonged and repeated 'partial' soil drying is applied and what role the rewatering-stimulated new root growth may play in sensing the repeated soil drying. The physiological and morphological alternation of plants under partial root-zone irrigation may bring more benefits to crops than improved water use efficiency where carbon redistribution among organs is crucial to the determination of the quantity and quality of the products.

Agriculture↗
PubMed1986

Bacteroids Are Stable during Dark-Induced Senescence of Soybean Root Nodules.

Physiological and biochemical markers of metabolic competence were assayed in bacteroids isolated from root nodules of control, dark-stressed, and recovered plants of Glycine max Merr. cv ;Woodworth.' Nitrogenase-dependent acetylene reduction by the whole plant decreased to 8% of control rates after 4 days of dark stress and could not be detected in plants dark stressed for 8 days. However, in bacteroids isolated anaerobically, almost 50% of initial acetylene reduction activity remained after 4 days of dark stress but was totally lost after 8 days of dark stress. Bacteroid acetylene reduction activity recovered faster than whole plant acetylene reduction activity when plants were dark stressed for 8 days and returned to a normal light regimen. Significant changes were not measured in bacteroid respiration, protein content, sodium dodecyl sulfate-polyacrylamide gel electrophoresis protein profiles, or in bacteroid proteolytic activity throughout the experiment. Immunoblots of bacteroid extracts revealed the presence of nitrogenase component II in control, 4-day dark-stressed, and 8-day dark-stressed plants that were allowed to recover under a normal light regimen, but not in 8-day dark-stressed plants. Our data indicate that dark stress does not greatly affect bacteroid metabolism or induce bacteroid senescence.

Journal Article↗
PubMed2001

Desulfomusa hansenii gen. nov., sp. nov., a novel marine propionate-degrading, sulfate-reducing bacterium isolated from Zostera marina roots.

The physiology and phylogeny of a novel sulfate-reducing bacterium, isolated from surface-sterilized roots of the marine macrophyte Zostera marina, are presented. The strain, designated P1T, was enriched and isolated in defined oxygen-free, bicarbonate-buffered, iron-reduced seawater medium with propionate as sole carbon source and electron donor and sulfate as electron acceptor. Strain P1T had a rod-shaped, slightly curved cell morphology and was motile by means of a single polar flagellum. Cells generally aggregated in clumps throughout the growth phase. High CaCl2 (10 mM) and MgCl2 (50 mM) concentrations were required for optimum growth. In addition to propionate, strain P1T utilized fumarate, succinate, pyruvate, ethanol, butanol and alanine. Oxidation of propionate was incomplete and acetate was formed in stoichiometric amounts. Strain P1T thus resembles members of the sulfate-reducing genera Desulfobulbus and Desulforhopalus, which both oxidize propionate incompletely and form acetate in addition to CO2. However, sequence analysis of the small-subunit rDNA and the dissimilatory sulfite reductase gene revealed that strain P1T was unrelated to the incomplete oxidizers Desulfobulbus and Desulforhopalus and that it constitutes a novel lineage affiliated with the genera Desulfococcus, Desulfosarcina, Desulfonema and 'Desulfobotulus'. Members of this branch, with the exception of 'Desulfobotulus sapovorans', oxidize a variety of substrates completely to CO2. Strain P1T (= DSM 12642T = ATCC 700811T) is therefore proposed as Desulfomusa hansenii gen. nov., sp. nov. Strain p1T thus illustrates the difficulty of extrapolating rRNA similarities to physiology and/or ecological function.

Biodegradation, Environmental↗
PubMed1985

Nerve cells of adult and aged mice grown in a monolayer culture: age-associated changes in morphological and physiological properties of dorsal root ganglion cells in vitro.

In order to differentiate age-associated changes in morphological and physiological properties of mammalian nerve cells, dorsal root ganglion (DRG) cells of aged mice (C57BL/6; 98-99 weeks old) were grown in a monolayer culture. Neurite outgrowth, changes in shape and size of their soma and functional properties of their plasma membranes were compared to those of tissue-cultured DRG cells from young adult mice (4-8 weeks old). Trigeminal root ganglion (TRG) cells of aged mice were also grown in a monolayer culture, and their in vitro growth was compared to that of the aged DRG cells. Nerve cells were dissociated from DRG (or TRG) by digestion with collagenase and by trituration and were grown on collagen-coated plastic dishes for more than 14 days. Growth of neurites and changes in the size and shape of the nerve cell soma were viewed under a phase-contrast microscope, and physiological properties of the plasma membrane were studied by conventional intracellular recordings with a glass microelectrode. Both adult and aged DRG cells grew neurites of various length and underwent changes in shape and size of their soma, which could be divided into 2 stages; early and late. In the early stage of tissue culture (0-60 h in vitro), nerve cells altered their shape from a spherical to a spindle-like form. This change was not associated with the reduction in cell size. In the late stage of the tissue culture (3-14 days and thereafter), the DRG reduced their cell size, while changes in shape remained small. Quantitative comparison of the adult and aged DRG nerve cells revealed the following 3 major differences between 2 cultures: the survival fraction of the aged DRG cells counted at 36-48 h in vitro was 1/4 to 1/10 of that of the adult DRG cells in 3 different tissue culture trials; reduction in the cell size occurred much earlier in the aged than in the adult nerve cells; the rate of reduction in size of the aged DRG cells was large in comparison with that of the adult DRG cells. No difference in neurite growth or in physiological properties (resting membrane potential, input resistance, input capacitance or capability of generating both Na and Ca spikes) was detected between the aged and adult nerve cells in tissue culture.

Aging↗
PubMed2004

Developmental physiology of cluster-root carboxylate synthesis and exudation in harsh hakea. Expression of phosphoenolpyruvate carboxylase and the alternative oxidase.

Harsh hakea (Hakea prostrata R.Br.) is a member of the Proteaceae family, which is highly represented on the extremely nutrient-impoverished soils in southwest Australia. When phosphorus is limiting, harsh hakea develops proteoid or cluster roots that release carboxylates that mobilize sparingly soluble phosphate in the rhizosphere. To investigate the physiology underlying the synthesis and exudation of carboxylates from cluster roots in Proteaceae, we measured O2 consumption, CO2 release, internal carboxylate concentrations and carboxylate exudation, and the abundance of the enzymes phosphoenolpyruvate carboxylase and alternative oxidase (AOX) over a 3-week time course of cluster-root development. Peak rates of citrate and malate exudation were observed from 12- to 13-d-old cluster roots, preceded by a reduction in cluster-root total protein levels and a reduced rate of O2 consumption. In harsh hakea, phosphoenolpyruvate carboxylase expression was relatively constant in cluster roots, regardless of developmental stage. During cluster-root maturation, however, the expression of AOX protein increased prior to the time when citrate and malate exudation peaked. This increase in AOX protein levels is presumably needed to allow a greater flow of electrons through the mitochondrial electron transport chain in the absence of rapid ATP turnover. Citrate and isocitrate synthesis and accumulation contributed in a major way to the subsequent burst of citrate and malate exudation. Phosphorus accumulated by harsh hakea cluster roots was remobilized during senescence as part of their efficient P cycling strategy for growth on nutrient impoverished soils.

Carbon Dioxide↗
PubMed1994

Cardiovascular physiology teaching: computer simulations vs. animal demonstrations.

The roots of physiology lie in laboratory observation, and physiology courses continue to rely on laboratory observation to provide students with practical information to correlate with their developing base of conceptual knowledge. To this end, animal laboratories provide a functioning example of interactions among organ systems and a source of data for student analysis. However, there are continuing objections to using animals for teaching, and animal labs are costly in time and effort. As an alternative laboratory tool, computer software can simulate the operation of multiple organ systems: responses to interventions illustrate intrinsic organ behavior and integrated systems physiology. Advantages of software over animal studies include alteration of variables that are not easily changed in vivo, repeated interventions, and cost-effective hands-on student access. Nevertheless, simulations miss intangible aspects of experimental physiology, and results depend critically on the assumptions of the model. We used both computer and animal demonstrations in teaching cardiovascular physiology to first-year medical students. The students rated both highly, but the computer-based session received a higher rating. We believe that both forms of teaching have educational merit. At the introductory level, the computer appears to provide an effective alternative.

Animals↗
PubMed2000

Physiological responses of radiata pine roots to soil strength and soil water deficit.

We investigated physiological responses of radiata pine (Pinus radiata D. Don) roots to soil strength and soil water deficit by measuring the osmotic potential (Psi(pi)) and yield turgor (Y) in the elongation zone of root segments of seedlings growing (i) in polyethylene glycol 4000-containing rooting solution of different water potentials (Psi(s)) and (ii) in soil of different soil strengths (Q) at the same soil matric potential (Psi(m)). Root elongation rate (Deltal/Deltat) decreased progressively with decreasing Psi(s) and was associated with decreased Psi(pi) and decreased turgor pressure (P). Osmotic adjustment occurred at Psi(s) < -0.2 MPa. Over a range in Psi(s) of -0.01 to -1.0 MPa, Psi(pi) fell 0.3 MPa whereas P fell 0.7 MPa. Mean Psi in the solution experiment was 0.37 MPa and did not differ significantly with Psi(s) (P = 0.10). Root elongation rate decreased exponentially as Q increased from 0 to 3.0 MPa, and was associated with an increase in P of 0.11 MPa as a consequence of Psi(pi) decreasing by the same amount. Mean Y in the soil experiment was 0.49 MPa and did not change significantly with Q (P = 0.87).

Journal Article↗
PubMed1977

Mechanosensitivity of dorsal root ganglia and chronically injured axons: a physiological basis for the radicular pain of nerve root compression.

The radicular pain of sciatica was ascribed by Mixter and Barr to compression of the spinal root by a herniated intervertebral disc. It was assumed that root compression produced prolonged firing in the injured sensory fibers and led to pain perceived in the peripheral distribution of those fibers. This concept has been challenged on the basis that acute peripheral nerve compression neuropathies are usually painless. Furthermore, animal experiments have rarely shown more than several seconds of repetitive firing in acutely compressed nerves or nerve roots. It has been suggested that "radicular pain" is actually pain referred to the extremity through activation of deep spinal and paraspinal nociceptors. Our experiments on cat lumbar dorsal roots and rabbit sural nerves have confirmed that acute compression of the root or nerve does not produce more than several seconds of repetitive firing. However, long periods of repetitive firing (5-25 min) follow minimal acute compression of the normal dorsal root ganglion. Chronic injury of dorsal roots or sural nerve produces a marked increase in mechanical sensitivity; several minutes of repetitive firing may follow acute compression of such chronically injured sites. Such prolonged responses could be evoked repeatedly in a population of both rapidly and slowly conducting fibers. Since mechanical compression of either the dorsal root ganglion or of chronically injured roots can induce prolonged repetitive firing in sensory axons, we conclude that radicular pain is due to activity in the fibers appropriate to the area of perceived pain.

Action Potentials↗