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PubMed2005

Root responses and metal accumulation in two contrasting ecotypes of Sedum alfredii Hance under lead and zinc toxic stress.

Sedum alfredii Hance has been reported to be a Zn-hyperaccumulator plant species. In this study, root morphological and physiological response of the hyperaccumulating ecotype of S. alfredii H. (HE) from the mined area and the non-hyperaccumulating ecotype of S. alfredii H. (NHE) from the agricultural area to supplied levels of Zn and Pb were investigated. The results showed that Zn concentrations in the leaves and the stems of the HE were 34 and 41 times higher, whereas lead concentrations were 1.9 and 2.4 times greater, respectively, than those of the NHE when grown at 1224 microM Zn and/or 200 microM Pb. At combined supply of 1224 microM Zn with 200 microM Pb, however, zinc concentrations in the stems and leaves of the, HE decreased, while lead concentrations in the stems increased significantly, as compared with those of single metal treatment. Lead uptake of the HE was enhanced by Zn addition. Root activity of the HE decreased by Pb treatment in the first two days, but recovered afterward and close to the control at day 10 of the treatment. However, root activity of the NHE decreased by each metal treatment, and was not recovered with the advance of treatment time. Root length, root surface area, and root volumes increased obviously due to Zn and/or Pb/Zn combined treatments for the HE, but significantly decreased due to Pb, Zn, or Pb/Zn combined treatment for the NHE. Zinc and Pb concentrations in both ecotypes of S. alfredii H. were positively correlated with root length, root surface area, and root volumes. Root exudates of the HE, especially treated with Zn, increased the extractability of Pb and Zn from the mined soil. At the Zn supply level of 1224microM, the extractability of root exudates on soil Pb was 3-12 times greater for the HE than for the NHE. These results imply that the tolerance and hyperaccumulation of the hyperaccumulating ecotype of S. alfredii H. to Zn and Pb appear to be closely related to its high adaptation of root growth, morphology, and physiology to Pb and Zn toxicity, and through its root excretion of some special substances that can activate Pb and Zn in the mined soil, thus increasing their mobilization and bioavailability.

Ecosystem↗
PubMed2005

Dynamics of heterorhizic root systems: protoxylem groups within the fine-root system of Chamaecyparis obtusa.

To understand the physiology of fine-root functions in relation to soil organic sources, the heterogeneity of individual root functions within a fine-root system requires investigation. Here the heterogeneous dynamics within fine-root systems are reported. The fine roots of Chamaecyparis obtusa were sampled using a sequential ingrowth core method over 2 yr. After color categorization, roots were classified into protoxylem groups from anatomical observations. The root lengths with diarch and triarch groups fluctuated seasonally, whereas the tetrarch root length increased. The percentage of secondary root mortality to total mortality increased with increasing amounts of protoxylem. The carbon : nitrogen ratio indicated that the decomposability of primary roots might be greater than that of secondary roots. The position of diarch roots was mostly apical, whereas tetrarch roots tended to be distributed in basal positions within the root architecture. We demonstrate the heterogeneous dynamics within a fine-root system of C. obtusa. Fine-root heterogeneity should affect soil C dynamics. This heterogeneity is determined by the branching position within the root architecture.

Carbon↗
PubMed1984

Morphology and synaptic relationships of physiologically identified low-threshold dorsal root axons stained with intra-axonal horseradish peroxidase in the cat and monkey.

The arborizations and synaptic relationships of intra-axonally stained horseradish peroxidase- (HRP) labeled primary afferent fibers to the dorsal horn of the cat and monkey spinal cord have been studied by light and electron microscopic methods. The light microscopic arborizations of the afferent fiber types (hair follicle afferents, pacinian corpuscle afferents, type I and type II slowly adapting afferents) are similar to those described by Brown and his colleagues (1) in the cat. The synaptic profiles formed by labeled afferents contain rounded synaptic vesicles. In serial thin sections, it was found that single dorsal root axons may make hundreds or thousands of synapses with neuronal structures of the dorsal horn. The vast majority of synaptic contacts are on the dendritic trees of dorsal horn neurons. The synapses made by these low-threshold afferent axons are almost all in the deeper laminae (III-VI) of the dorsal horn. The hair follicle afferent axons and the pacinian corpuscle afferents have numerous vesicle-containing structures that synapse on them to form either axoaxonal synapses or dendroaxonal synapses. The slowly adapting afferent axons are less often found to be postsynaptic to axons or dendrites. It is concluded that different physiological classes of primary afferent axons have different morphological characteristics, both at the light and electron microscopic level.

Afferent Pathways↗
PubMed1975

Characteristics of Streptococcus milleri and Streptococcus mitior from infected dental root canals.

Morphological and physiological characteristics of 103 streptococcal isolates obtained from positive routine cultures of material from dental root canals at filling, were studied. The majority of the isolates were those which at a primary identification not fullfilled the criteria of enterococci, Strep. sanguis, Strep. mutans or Strep. salivarius. Only a few representative strains of the latter types were included in the study as a control of the method. The resemblance of the 103 isolates to 38 reference strains were assessed with numerical methods. The isolates formed 9 clusters with reference strains occurring in all but one. Of the isolates which it was intended to identify and characterize with numerical taxonomic analysis, all but one joined one of 3 clusters and were identified as Strep. milleri or Strep. mitior (mitis). The most useful cultural characteristics to dfferentiate the two species were growth on the sulphonamide containing MC-agar and 7.5% bile blood agar by Strep. milleri and production of hydrogen peroxide by Strep. mitior. The characteristics of the strains in the nine 80-phenons are given in Table 2. Other characteristics that appeared to be of interest for differentiating Strep. milleri from Strep. mitior and these two species from other viridans streptococci are underlined in Table 2. Strep. milleri seems not earlier to have been reported to occur in infected root canals. The occurrence of Strep. milleri is in agreement with the data given on serological groups found among streptococcal isolates from routine root canal cultures. Little is known about the occurrence and distribution of Strep. milleri in the human oral cavity, which therefore warrant further investigations.

Dental Pulp Cavity↗
PubMed2026

Turnip mosaic virus alters phosphorus metabolism and shoot-root allocation without resource competition.

Plant viruses affect production through symptom induction in host plants. These symptoms could partially arise from nutrient deprivation: The resource competition hypothesis posits that massive viral replication deprives hosts of essential nutrients, yet direct evidence for phosphorus (P) competition is lacking. Moreover, it is reported that biotic stresses can lead to alterations on P metabolism. Using a hydroponic system enabling separate analysis of shoots and roots in adult Arabidopsis thaliana plants, we investigated whether Turnip mosaic virus (TuMV) drawed significant P internal pools leading to P competition or altered P metabolism. TuMV genomic RNA represented < 0.3% of the P pool allocated to 18S rRNA, refuting the resource competition hypothesis. Instead, TuMV induced a marked shoot-to-root P redistribution: Shoot/Root Pi and Porg changed from 1.7 to 1.04 to 0.71 and 0.68, respectively. This altered partitioning correlated with organ-specific gene expression changes: high-affinity transporters PHT1; 4 and PHT1; 5 were co-induced in shoots, whereas immunity-related PHT1; 4 was uniquely repressed in roots. The senescence-associated gene SEN1 showed opposite regulation between organs (repressed in shoots, induced in roots), distinguishing virus-induced responses from canonical senescence. Multivariate analysis revealed that shoots and roots only partially share physiological and molecular responses to TuMV. The virus reprograms phosphorus metabolism through organ-specific changes, not through resource depletion, and roots act as a distinct hub integrating infection response, senescence, and nutrient dynamics. This study advances the understanding of growth-defense trade-offs in plant mineral nutrition and identifies new targets for maintaining crop productivity under biotic stress.

Arabidopsis↗
PubMed1990

Square root intensity coding in turtle cones: physiological mechanisms.

The effect of coupling on the intensity-response functions for full field and for slit stimuli was studied by comparing the shapes of the curves obtained from several strongly coupled red cones of turtle with that of one very weakly coupled cone. The full field V-log I curves could be fitted by a Michaelis-Menten relationship, regardless of the strength of the coupling. For the weakly coupled cone the slit V-log I could also be fitted by a Michaelis-Menten curve. For strongly coupled cones a major portion of the curve (1.2-2 log units of intensity) was better fitted by V oc Im. For centered slits "m" was 0.5. With increased distance between the slit and the center of the receptive field "m" was found to increase slightly. The results were analyzed in terms of a theory in which the shape of the slit intensity-response curves arises from scattered light progressively recruiting neighboring cone responses. An analytical formulation of this idea is presented and a plausible light distribution function which supports the recruitment hypothesis is derived. A numerical model of the cone network, which includes the effect of scattering and transduction saturation, accounts well for all of the experimental data obtained with single and paired slits.

Animals↗
PubMed1998

Regulation of symbiotic root nodule development.

Symbiosis between rhizobia and leguminous plants leads to the formation of N2-fixing root nodules. The interaction of rhizobia and plants shows a high degree of host specificity based on the exchange of chemical signals between the symbiotic partners. The plant signals, flavonoids exuded by the roots, activate the expression of nodulation genes, resulting in the production of the rhizobial lipochitooligosaccharide signals (Nod factors). Nod factors act as morphogens that, under conditions of nitrogen limitation, induce cells within the root cortex to divide and to develop into nodule primordia. This review focuses on how the production of Nod factors is regulated, how these signals are perceived and transduced by the plant root, and the physiological conditions and plant factors that control the early events leading to root nodule development.

Fabaceae↗
PubMed1982

Physiological properties of dystrophic mouse spinal root axons.

In the spinal root axons of dystrophic mice conduction of nerve impulses is slow and either saltatory or continuous, presumably corresponding to areas of myelination and amyelination respectively. These abnormally myelinated axons contain foci of hyperexcitability manifested by spontaneous ectopic excitation, ephaptic excitation and autoexcitation. Similar phenomena in demyelinated central and peripheral nerve fibres may underly positive neurological symptomatology in human peripheral and central demyelinating diseases (Rasminsky 1981, 1982).

Animals↗
PubMed2006

Morpho-anatomical, physiological and biochemical adjustments in response to root zone salinity stress and high solar radiation in two Mediterranean evergreen shrubs, Myrtus communis and Pistacia lentiscus.

Salt- and light-induced changes in morpho-anatomical, physiological and biochemical traits were analysed in Myrtus communis and Pistacia lentiscus with a view to explaining their ecological distribution in the Mediterranean basin. In plants exposed to 20 or 100% solar radiation and supplied with 0 or 200 mm NaCl, measurements were conducted for ionic and water relations and photosynthetic performance, leaf morpho-anatomical and optical properties and tissue-specific accumulation of tannins and flavonoids. Net carbon gain and photosystem II (PSII) efficiency decreased less in P. lentiscus than in M. communis when exposed to salinity stress, the former having a superior ability to use Na(+) and Cl(-) for osmotic adjustment. Morpho-anatomical traits also allowed P. lentiscus to protect sensitive targets in the leaf from the combined action of salinity stress and high solar radiation to a greater degree than M. communis. Salt and light-induced increases in carbon allocated to polyphenols, particularly to flavonoids, were greater in M. communis than in P. lentiscus, and appeared to be related to leaf oxidative damage. Our data may conclusively explain the negligible distribution of M. communis in open Mediterranean areas suffering from salinity stress, and suggest a key antioxidant function of flavonoids in response to different stressful conditions.

Carbon↗
PubMed2003

p-Chlorophenoxyisobutyric acid impairs auxin response in Arabidopsis root.

p-Chlorophenoxyisobutyric acid (PCIB) is known as a putative antiauxin and is widely used to inhibit auxin action, although the mechanism of PCIB-mediated inhibition of auxin action is not characterized very well at the molecular level. In the present work, we showed that PCIB inhibited BA::beta-glucuronidase (GUS) expression induced by indole-3-acetic acid (IAA), 2,4-dichlorophenoxyacetic acid, and 1-naphthaleneacetic acid. PCIB also inhibited auxin-dependent DR5::GUS expression. RNA hybridization and quantitative reverse transcriptase-polymerase chain reaction analyses suggested that PCIB reduced auxin-induced accumulation of transcripts of Aux/IAA genes. In addition, PCIB relieved the reduction of GUS activity in HS::AXR3NT-GUS transgenic line in which auxin inhibits GUS activity by promoting degradation of the AXR3NT-GUS fusion protein. Physiological analysis revealed that PCIB inhibited lateral root production, gravitropic response of roots, and growth of primary roots. These results suggest that PCIB impairs auxin-signaling pathway by regulating Aux/IAA protein stability and thereby affects the auxin-regulated Arabidopsis root physiology.

2,4-Dichlorophenoxyacetic Acid↗
PubMed1996

Cytochemical assay for differential respiratory activity in roots and root hairs.

The study of the underground parts of plants is often difficult, and as a result roots are often treated as homogeneous physiological entities with respect to root respiration. In this study we demonstrate a partitioning of respiration within root tissues using nitro blue tetrazolium staining and an incident light optical system that permits detailed observations of intact roots. The assay is rapid and easy to perform, and reveals that respiratory activity in roots is not uniform in space and time. The results show that root hairs in particular may be regions of enhanced respiratory activity in some species or in certain developmental or physiological states. This fact has important implications for the role of root hairs in the overall respiratory budget of roots and the energetics of nutrient assimilation. The results suggest that root respiration studies should consider differential respiratory activities of root cell types within roots.

Adenosine Triphosphate↗
PubMed2001

Ion-exchange properties of cell walls isolated from lupine roots.

Acid-base properties of cell walls isolated from various root tissues of 7-day-old lupine seedlings and 14-day-old lupine plants grown in various media were studied. The ion-exchange capacity of root cell walls was estimated at various pH values (from 2 to 12) and constant ionic strength (10 mM). The parameters determining the qualitative and quantitative composition of cell wall ionogenic groups along the root length and in its radial direction were estimated using Gregor's model. This model fits the experimental data reasonably well. Four types of ionogenic groups were found in the cell walls: an amino group (pKa approximately 3), two types of carboxylic groups (pKa approximately 5 and 7.3, the first being the carboxylic group of galacturonic acid), and a phenolic group (pKa approximately 10). The number of functional groups of each type was estimated, and the corresponding ionization constant values were calculated. It is shown that the chemical composition of the ionogenic groups was constant along the root length as well as in its radial direction and did not depend on either physiological state or root nutrition, while the number of different groups varied. The content of carboxylic groups of alpha-D-polygalacturonic acid in the root cell walls of 14-day-old plants was shown to depend on the distance from the root tip, being maximal in the zone of lateral roots. The number of these groups was 10- and 2-fold less in the central cylinder compared to that of cortex for 14-day-old plants and 7-day-old seedlings, respectively.

Amino Acids↗
PubMed1976

Octopamine release at two points along lobster nerve trunks.

Nerve cells in the proximal regions of second thoracic roots in lobsters have been injected with the fluorescent dye Procion Yellow. Examination of the roots reveals an elaborate array of cell branches in a superficial layer of the root in the vicinity of the cell bodies. Large varicosities, up to 10 mum in diameter, are seen lined up along fine nerve branches. 2. In these same regions, electron microscopic examination shows the presence of large profiles filled with 0-1-0-2 mum dense cored granules, and having the appearance of nerve endings. These profiles probably correspond to the varicosities seen in the Procion Yellow injections. The dense cored granules within the endings have a crystalline substructure. All the endings are found within 7 mum of the surface of the root and no obvious physiological target tissue exists in their surroundings. Endings have not been traced directly to root cell bodies.However, granules of similar dimensions to those seen in endings are found in cell bodies, axon-hillock regions and numerous axonal profiles in the superficial root regions near cell bodies. The morphological studies suggest that the root neurones have the typical appearance of neurosecretory cells. 3. Octopamine pools in cell body regions of second thoracic roots can be isotopically labelled by incubation with either [3H]tyramine or [3H]-tyrosine. After labelling, pulsing with 100 mM potassium causes an increase in the rate of release of radioactive material. Upon return to normal media background rates of release are re-established. The enhanced efflux has the following properties: (a) repeated pulses of potassium release less radio-active material each time; (b) a prolonged potassium pulse produces first a peak of release, then a decline to a plateau, and the plateau level of release is maintained for the duration of the potassium pulse; (c) release is dependent on the presence of calcium ions in the bathing fluid and 40 mM cobalt prevents release; (d) release is selective for octopamine. With tyrosine as a precursor compound, as much radioactive tyrosine as octopamine is found in tissues after incubation, yet pulsing with potassium causes an enhanced efflux only of octopamine from preparations. 4. Release of octopamine also can be demonstrated from pericardial organs near the ends of lateral branches of the roots and the properties of the release are identical to those seen with cell body regions. 5. Physiological studies, in which root cells are antidromically activated while recording from cell bodies, suggest that the distal endings of at least some of the root cells are at the pericardial organs. 6. The results suggest that root cell neurones are neurosecretory cells capable of releasing octopamine at two points: one near cell bodies, the other at the pericardial organs near the distal ends of the roots...

Animals↗
PubMed2000

Abnormalities of the soleus H-reflex in lumbar spondylolisthesis: a possible early sign of bilateral S1 root dysfunction.

Using routine electrodiagnostic procedures, the authors searched for physiologic evidence of nerve root compromise in patients with chronic mechanical perturbation to the lumbar spine. They examined 37 patients with spondylolisthesis and various degrees of degenerative changes in the lumbar canal. Clinical and neurophysiologic findings were compared with data obtained from 36 healthy persons. The soleus H-reflex appeared to be a sensitive indicator of sensory fiber compromise at the S1 root level, because changes correlated well with the focal sensory signs and preceded clinical and electromyographic signs of motor root involvement. When these occurred, the clinical findings were consistent with a more severe nerve root deficit and with radiographic evidence of neural compression. The greater sensitivity of the soleus H-reflex may be related to the pathophysiologic events that occur at the lesion site.

Adult↗