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PubMed2005

Cluster roots of Leucadendron laureolum (Proteaceae) and Lupinus albus (Fabaceae) take up glycine intact: an adaptive strategy to low mineral nitrogen in soils?

BACKGROUND AND AIMS: South African soils are not only low in phosphorus (P) but most nitrogen (N) is in organic form, and soil amino acid concentrations can reach 2.6 g kg(-1) soil. The Proteaceae (a main component of the South African Fynbos vegetation) and some Fabaceae produce cluster roots in response to low soil phosphorus. The ability of these roots to acquire the amino acid glycine (Gly) was assessed. METHODS: Uptake of organic N as 13C-15N-Gly was determined in cluster roots and non-cluster roots of Leucadendron laureolum (Proteaceae) and Lupinus albus (Fabaceae) in hydroponic culture, taking account of respiratory loss of 13CO2. KEY RESULTS: Both plant species acquired doubly labelled (intact) Gly, and respiratory losses of 13CO2 were small. Lupin (but not leucadendron) acquired more intact Gly when cluster roots were supplied with 13C-15N-Gly than when non-cluster roots were supplied. After treatment with labelled Gly (13C : 15N ratio = 1), lupin cluster roots had a 13C : 15N ratio of about 0.85 compared with 0.59 in labelled non-cluster roots. Rates of uptake of label from Gly did not differ between cluster and non-cluster roots of either species. The ratio of C : N and 13C : 15N in the plant increased in the order: labelled roots < rest of the root < shoot in both species, owing to an increasing proportion of 13C translocation. CONCLUSIONS: Cluster roots of lupin specifically acquired more intact Gly than non-cluster roots, whereas Gly uptake by the cluster and non-cluster roots of leucadendron was comparable. The uptake capacities of cluster roots are discussed in relation to spatial and morphological characteristics in the natural environment.

Carbon Radioisotopes↗
PubMed2006

The effect of silicon on the infection by and spread of Pythium aphanidermatum in single roots of tomato and bitter gourd.

The effect of silicon (Si) supply on the infection and spread of Pythium aphanidermatum was studied in the roots of tomato [Lycopersicon esculentum (=Solanum lycopersicum), an Si excluder] and bitter gourd (Mormodica charantia, an Si intermediate accumulator). Individual roots were mounted into PVC compartmented boxes which allowed the application of Si and zoospores to defined root zones. Two days after inoculation, root growth was recorded, and P. aphanidermatum colonization of individual root sections was determined by ELISA. In tomato as well as in bitter gourd the root tip was the root section most sensitive to P. aphanidermatum infection. Application of Si did not affect severe root-growth inhibition by P. aphanidermatum in either species. However, continuous Si supply significantly inhibited the basipetal spread of the pathogen from the infected root apex in bitter gourd but not in tomato. Si application to the roots only during pretreatment or only during/after the infection of the roots failed to inhibit the spread of P. aphanidermatum. Determination and compartmentation of Si in the roots of bitter gourd revealed that apoplastic Si was not, but symplastic Si was, associated with the ability of the plant to reduce the spread of the fungus in roots. It is concluded that accumulation of Si in the root cell walls does not represent a physical barrier to the spread of P. aphanidermatum in bitter gourd and tomato roots. The maintenance of elevated symplastic Si contents is a prerequisite for Si-enhanced resistance against P. aphanidermatum.

Antiparasitic Agents↗
PubMed2004

Root distribution of Pinus pinaster, P. radiata, Eucalyptus globulus and E. kochii and associated soil chemistry in agricultural land adjacent to tree lines.

We quantified the extent and distribution of roots of four commonly planted tree species (Eucalyptus globulus Labill., Pinus radiata D. Don, P. pinaster Aiton and E. kochii Maiden & Blakely subsp. plenissima C.A. Gardner) in agricultural land adjacent to tree lines, and examined the effect of soil type and root pruning on root morphology. Root distribution in soil adjacent to tree lines was mapped by a trench profile method at 13 sites on the south coast of Western Australia. Soil samples were collected to determine water content and fertility. The lateral extent of tree roots ranged from 10 m for E. kochii to 44 m for P. pinaster. This equated to between 1.5 and 2.5 times tree height (H) for E. globulus and Pinus spp. to 4H for E. kochii. Root density declined logarithmically with distance from the trees and was greatest for P. pinaster and least for E. globulus (P < 0.001). The rate of decrease in root density with distance from the trees was greatest for the Pinus spp. and least for E. kochii (P < 0.05). Root density was generally greatest in the top 0.5 m of the soil profile and decreased with increasing depth. This decrease was relatively gradual in the deep sands, but abrupt in clay subsoil. Root dry mass in the sandy top soil beyond 0.5H ranged between 1.0 and 55.5 Mg km(treeline) (-1) for 6-year-old E. kochii and 50-year-old P. pinaster, respectively. Soil water content generally increased with distance from the trees (P < 0.001). There was no evidence of reduced soil fertility in the top 1.4 m of the soil profile adjacent to the trees. Two to four years after trees had been root pruned, both the lateral extent and vertical distribution of roots were similar for pruned and unpruned trees. The density of roots < 2 mm in diameter was greater for root-pruned trees than for unpruned trees (P < 0.05). We conclude that the study species can compete with agricultural crops based on the lateral extent of their roots and the occurrence of greatest root density within 0.5 m of the soil surface.

Biomass↗
PubMed2006

Photosynthesis and photoassimilate transport during root hypoxia in Melaleuca cajuputi, a flood-tolerant species, and in Eucalyptus camaldulensis, a moderately flood-tolerant species.

We compared the photosynthetic and photoassimilate transport responses of Melaleuca cajuputi Powell seedlings to root hypoxia with those of Eucalyptus camaldulensis Dehnh. Control and hypoxia treated roots were maintained in a nutrient solution through which air or nitrogen was bubbled. Under root hypoxic conditions, seedlings of M. cajuputi, a flood-tolerant species, maintained height growth, whereas seedlings of E. camaldulensis, a moderately flood-tolerant species, showed markedly decreased height growth compared with control seedlings. Root hypoxia caused decreases in whole-plant biomass, photosynthetic rate and stomatal conductance in E. camaldulensis, but not in M. cajuputi. Photoassimilate transport to roots decreased significantly in E. camaldulensis seedlings 4 days after treatment and starch accumulated in mature leaves. Photoassimilate supply to hypoxic roots of E. camaldulensis seedlings was, thus, limited by reduced photoassimilate transport rather than by reduced photosynthesis. In contrast, M. cajuputi seedlings showed sustained photoassimilate transport to hypoxic roots and persistent photosynthesis, which together provided a substantial photoassimilate supply to the roots. Sucrose accumulated in hypoxic E. camaldulensis roots, but not in hypoxic M. cajuputi roots. A stable, low sucrose concentration in hypoxic roots would let M. cajuputi seedlings prolong photoassimilate transport to the roots. Photoassimilate partitioning among the water-soluble carbohydrates, starch and structural carbohydrates within the roots was unaffected by root hypoxia in E. camaldulensis, but in M. cajuputi, partitioning was shifted somewhat from structural carbohydrates to water-soluble carbohydrates. This suggests that M. cajuputi seedlings are able to increase photoassimilate utilization in metabolism and sustain energy production under root hypoxic conditions.

Alcohol Dehydrogenase↗
PubMed2000

Motor response of the leg muscles produced by position-selective stimulation of spinal nerve roots.

OBJECTIVE: To define and measure motor responses of the leg muscles in the ankle associated with position-selective and tetanic stimulation of spinal nerve roots L3-S1. METHODS: Sixteen lumbosacral spinal nerve roots in 14 subjects were stimulated intraoperatively after surgical exposure and decompression for a herniated disc. Each contact of a spiral cuff multielectrode was wrapped around the root and used to excite a spatially defined population of axons beneath the electrode. The motor response from each stimulated position was evaluated in terms of three-dimensional vector torque in the ankle. RESULTS: Each position at which the stimulating electrode was placed around the root exhibited the same vector torque qualitatively, but at different thresholds. The root was most excitable ventrally. The S1 roots responded with a uniform three-dimensional torque pattern: plantar flexion plus lateral leg and foot rotation plus inversion. All L5 roots responded by plantar flexion. Dorsiflexion torque was possible only with stimulation of the L3 and L4 roots. Eversion was not possible with stimulation of the S1 roots or with most of the L5 roots. CONCLUSION: Position-selective stimulation of the extrathecal spinal nerve roots influences the threshold of the biomechanical response, the torque recruitment dynamics, and the magnitude of three-dimensional vector torque. Selective activation of some leg muscles or agonist muscle groups with stimulation of a single nerve root could not be achieved owing to the low spatial selectivity of the stimulation design and/or the low muscle specificity of motor fascicles in the root. Direct extrathecal stimulation of spinal nerve roots has some hypothetical advantages over stimulation of other sites along the peripheral nerves, owing to their unique anatomy, and may contribute to functional electrical stimulation of the lower extremities. Further investigation with a more selective multielectrode configuration and the use of multiple root stimulation is suggested.

Adult↗
PubMed1994

Experimental lumbar radiculopathy. Behavioral and histologic changes in a model of radicular pain after spinal nerve root irritation with chromic gut ligatures in the rat.

OBJECTIVE: The recently proposed animal model of lumbar radiculopathy was used to investigate behavioral consequences and histologic changes in spinal nerve roots, dorsal root ganglia, and spinal nerves after the L4, L5, and L6 nerve roots were loosely ligated with either silk or chromic gut sutures in an attempt to better understand the pathophysiologic mechanisms that give rise to pain associated with lumbar radiculopathy. SUMMARY OF BACKGROUND DATA: Little is known about the pathophysiologic mechanisms that give rise to pain associated with lumbar radiculopathy. The recently proposed animal model of unilateral lumbar radiculopathy, which demonstrated an association with motor paresis and thermal hyperalgesia of the affected hind limb and showed evidence of spontaneous pain has been demonstrated, may serve as a vehicle to allow direct investigation of the nature of the pathophysiological mechanisms associated with lumbar radiculopathy. METHODS: Three distinct treatments of the nerve roots were initially investigated: 1) a sham intervention, where the surgery simply exposed the nerve roots and dorsal root ganglion followed by standard closing procedures; 2) 4-0 silk ligature, where two loose ligatures of 4-0 silk were placed around the nerve roots; and 3) 4-0 chromic gut 2, where four 0.3 cm pieces of 4-0 chromic gut were laid adjacent to the nerve roots and secured by two loose ligatures of 4-0 chromic gut. STUDY DESIGN: ANOVA techniques were used to test for differential effects across time for the three treatment groups in terms of animal function. A qualitative analysis of the histology of the ipsilateral and contralateral nerve roots, dorsal root ganglia, and spinal nerves was done to correlate histologic changes with behavioral changes. RESULTS: Behavioral results were consistent with the previous study. Rats treated with chromic gut, but not silk, reliably demonstrated a prolonged thermal hyperalgesia that was maximal 2 weeks after surgery and lasted for up to 12 weeks. These behavioral changes, however, were not correlated with histologic changes in myelinated fiber content in the L4, L5, and L6 nerve roots, dorsal root ganglia and spinal nerves, the ipsilateral spinal nerved, dorsal root ganglia, and nerve roots of rates ligated with silk or chromic gut showed similar, significant, decreased in the number of large diameter myelinated fibers. CONCLUSIONS: These results suggest that mechanical constriction of the L4, L5, and L6 spinal nerve roots, as evidenced by a loss of myelinated fibers, is not sufficient to produce the behavioral effects associated with this model of lumbar radiculopathy. It is hypothesized that chemical factors from the chromic gut play a role in the pathophysiology and development of the behavioral, but not histological, changes in this model of lumbar radiculopathy.

Animals↗
PubMed1995

Neuropeptide changes in compressed spinal nerve roots.

STUDY DESIGN: Compression-induced changes in the concentration of substance P and VIP (vasoactive intestinal polypeptide), in spinal nerve roots and dorsal root ganglia were studied in an experimental nerve root compression model in pigs. OBJECTIVES: To analyze by radioimmunoassay the concentration of the neuropeptides substance P and VIP in a model for experimental chronic nerve root compression. SUMMARY OF BACKGROUND DATA: Neuropeptides such as substance P and VIP seem to be involved in the transmission of pain and changes in the levels of these neuropeptides have been described in models where peripheral or spinal nerve injury was induced. METHODS: An ameroid constrictor was applied on a spinal nerve root just cranial to the dorsal root ganglion. The inner diameter of this constrictor is gradually reduced. After 1 or 4 weeks, tissue samples were taken from the nerve root cranial to the constrictor and from the dorsal root ganglion for measurement of substance P and VIP concentrations. RESULTS: There was a statistically significant increase in substance P concentrations in the compressed dorsal root ganglia when compared to the noncompressed dorsal root ganglia at both 1 and 4 weeks. Substance P concentration was also significantly increased in the nerve root after 1 but not after 4 weeks. The VIP levels were not significantly changed in either tissue. CONCLUSIONS: The results of the study indicates an increase in substance P levels in the dorsal root ganglion (after 1 and 4 weeks) and in the nerve root (after 1 week) in a model for chronic nerve root compression in pigs. There were no significant differences in the VIP concentrations. The study thus indicates that changes in substance P are related to experimental chronic nerve root compression.

Animals↗
PubMed2006

Intrathecal movement and tension of the lumbosacral roots induced by straight-leg raising.

OBJECTIVE: To obtain quantitative biomechanical data on the effects of different angles of straight-leg raising on intrathecal movements and tensions in the lumbosacral nerve roots in human cadavers. DESIGN: Eight embalmed human cadavers with no gross spinal pathology and no limitations in hip motion were used. We performed reverse straight-leg raising by hanging the left leg down from the table with the knee extended while measuring the movement and tension of nerve roots L2, L3, L4, L5, and S1 in 10-degree intervals for straight-leg raising from 0 to 70 degrees. RESULTS: The mean intrathecal movements at 70 degrees were 0.55 mm, 0.54 mm, 0.96 mm, 1.54 mm, and 2.31 mm for roots L2, L3, L4, L5, and S1, respectively. The movements were statistically significant at >50 degrees for root L5 and at >40 degrees for root S1 (P < 0.05). The tension in the nerve roots with increasing angle of straight-leg raising increased from roots L2 to S1. The mean tensions at 70 degrees of straight-leg raising were 141.25 g, 168.75 g, 228.75 g, 280.00 g, and 493.75 g for roots L2, L3, L4, L5, and S1, respectively. The difference in tension was significant at >70 degrees for roots L2, L3, and L4 roots, at >40 degrees for root L5 root, and at >10 degrees for root S1 (P < 0.05). CONCLUSIONS: The intrathecal movement and tension of the lumbosacral roots induced by straight-leg raising were <2.5 mm and <500 g, respectively. The movement and tension induced by straight-leg raising tended to be greater in more distal segmental roots.

Biomechanical Phenomena↗
PubMed2005

An auxin transport independent pathway is involved in phosphate stress-induced root architectural alterations in Arabidopsis. Identification of BIG as a mediator of auxin in pericycle cell activation.

Arabidopsis (Arabidopsis thaliana) plants display a number of root developmental responses to low phosphate availability, including primary root growth inhibition, greater formation of lateral roots, and increased root hair elongation. To gain insight into the regulatory mechanisms by which phosphorus (P) availability alters postembryonic root development, we performed a mutant screen to identify genetic determinants involved in the response to P deprivation. Three low phosphate-resistant root lines (lpr1-1 to lpr1-3) were isolated because of their reduced lateral root formation in low P conditions. Genetic and molecular analyses revealed that all lpr1 mutants were allelic to BIG, which is required for normal auxin transport in Arabidopsis. Detailed characterization of lateral root primordia (LRP) development in wild-type and lpr1 mutants revealed that BIG is required for pericycle cell activation to form LRP in both high (1 mm) and low (1 microm) P conditions, but not for the low P-induced alterations in primary root growth, lateral root emergence, and root hair elongation. Exogenously supplied auxin restored normal lateral root formation in lpr1 mutants in the two P treatments. Treatment of wild-type Arabidopsis seedlings with brefeldin A, a fungal metabolite that blocks auxin transport, phenocopies the root developmental alterations observed in lpr1 mutants in both high and low P conditions, suggesting that BIG participates in vesicular targeting of auxin transporters. Taken together, our results show that auxin transport and BIG function have fundamental roles in pericycle cell activation to form LRP and promote root hair elongation. The mechanism that activates root system architectural alterations in response to P deprivation, however, seems to be independent of auxin transport and BIG.

Arabidopsis↗
PubMed2004

Cytokinins play opposite roles in lateral root formation, and nematode and Rhizobial symbioses.

We used the cytokinin-responsive Arabidopsis response regulator (ARR)5 gene promoter fused to a beta-glucuronidase (GUS) reporter gene, and cytokinin oxidase (CKX) genes from Arabidopsis thaliana (AtCKX3) and maize (ZmCKX1) to investigate the roles of cytokinins in lateral root formation and symbiosis in Lotus japonicus. ARR5 expression was undetectable in the dividing initial cells at early stages of lateral root formation, but later we observed high expression in the base of the lateral root primordium. The root tip continues to express ARR5 during subsequent development of the lateral root. These results suggest a dynamic role for cytokinin in lateral root development. We observed ARR5 expression in curled/deformed root hairs, and also in nodule primordia in response to Rhizobial inoculation. This expression declined once the nodule emerged from the parent root. Root penetration and migration of root-knot nematode (RKN) second-stage larvae (L2) did not elevate ARR5 expression, but a high level of expression was induced when L2 reached the differentiating vascular bundle and during early stages of the nematode-plant interaction. ARR5 expression was specifically absent in mature giant cells (GCs), although dividing cells around the GCs continued to express this reporter. The same pattern was observed using a green fluorescent protein (GFP) reporter driven by the ARR5 promoter in tomato. Overexpression of CKX genes rendered the transgenic hairy roots resistant to exogenous application of the cytokinin [N6-(Delta2 isopentenyl) adenine riboside] (iPR). CKX roots have significantly more lateral roots, but fewer nodules and nematode-induced root galls per plant, than control hairy roots.

Animals↗
PubMed1997

Types and dimensions of root trunk correlating with diagnosis of molar furcation involvements.

The objective of the present study was to investigate the possible correlation of dimension, location, prevalence, and types of root trunk with molar furcation involvement (FI). The samples used in the study include 166 maxillary molars (70 1st and 96 2nd molars) and 200 mandibular molars (103 1st and 97 2nd molars). The dimensions of the root trunks and root lengths were measured with an electric caliper and their means and standard deviations calculated. The types of root trunks were identified by the ratio of root trunk dimension to root length and classified as types A, B, and C. The results may be summarized as follows. (1) Short-root trunks were more commonly found buccally, whereas long-root trunks were more commonly found mesially, in both maxillary molars. (2) Short-root trunks were most commonly found buccally, whereas long-root trunks were more commonly found lingually in both mandibular molars. (3) Long-root trunks were more commonly found on the 2nd molars than on the 1st molars. (4) Long-root trunks were associated with short root length. (5) There is a strong correlation between vertical length and type of root trunk and FI. The findings of the study indicated that an awareness of root trunk type together with horizontal and vertical attachment levels in molar FI may be helpful in the prognosis, diagnosis, and treatment of molar FI.

Adult↗
PubMed1990

A quantitative study of the central projection patterns of unmyelinated ventral root afferents in the cat.

1. The ventral roots of the spinal cord contain a large number of unmyelinated primary afferent neurones. There is some controversy, however, about the function of these fibres and the route of their central projection. Here we have used electrophysiological techniques to quantify the central projection patterns of these neurones in the segment S2 of adult chloralose-anaesthesized cats. 2. A total of 1185 single unmyelinated units were recorded in small filaments isolated from intact and de-efferented ventral roots or intact dorsal roots of the segment S2 in nineteen cats. The projection patterns of these neurones were tested using supramaximal electrical stimulation of the pelvic and pudendal nerve (the main tributaries of the spinal nerve of this segment) and of the segmental companion root (dorsal or ventral as appropriate). 3. The principal finding of this study is that 85% of unmyelinated afferent axons in the ventral root are direct and exclusive projections. They constitute a separate class of afferents which is only capable of transmitting information from the periphery via the ventral roots. However, the proportion of these fibres that enter the central nervous system is unknown and it seems likely that some of them peter out as they approach the spinal cord and end blindly. The functional role of such afferents remains obscure. 4. For the remaining 15% of unmyelinated ventral root afferents, a projection into the segmental dorsal root was found. The majority of those fibres (about two-thirds) are primary afferent neurones innervating the pia mater. Some of these units had a small spot-like receptive field and responded to mechanical stimuli such as pressure and stretch of the root. They did not have axon projections in a peripheral nerve. 5. A few (5%) unmyelinated ventral root fibres are collateral branches of normal primary afferents projecting through the dorsal root. These trifurcating neurones are a small population which make up only some 0.5% of all dorsal root ganglion cells. The functional significance of this population too is unknown. 6. For none of the fibres that projected into both dorsal and ventral root was there positive evidence for the existence of looping axons that merely make a detour into one of the roots. Although the existence of loops cannot completely be excluded, our evidence suggests that they can constitute at most 5% of the unmyelinated ventral root afferents.

Action Potentials↗
PubMed2006

Roots of pioneer trees in the lower sub-tropical area of Dinghushan, Guangdong, China.

Representative pioneer tree root systems in the subtropical area of South China were examined with regard to their structure, underground stratification and biomass distribution. Excavation of skeleton roots and observation of fine roots of seven species including the Euphorbiaceae, Theaceae, Melastomataceae, Lauraceae and Fagaceae families was carried out. The results showed that: (1) Pioneer tree roots in the first stage of natural succession were of two types, one characterized by taproot system with bulky plagiotropic branches; the other characterized by flat root system with several tabular roots. The late mesophilous tree roots were characterized by one obvious taproot and tactic braches roots up and down. Shrub species roots were characterized by heart fibrous root type featured both by horizontally and transversally growing branches. Root shapes varied in different dominant species at different stages of succession. (2) Roots of the different species varied in the external features-color, periderm and structure of freshly cut slash. (3) In a set of successional stages the biomass of tree roots increased linearly with the age of growth. During monsoon, the total root biomass amounted to 115.70 t/ha in the evergreen broad-leaved forest; 50.61 t/ha in needle and broad-leaved mixed forest dominated by coniferous forest; and 64.20 t/ha in broad-and needle-leaved mixed forest dominated by broad-leaved heliophytes, and are comparable to the underground biomass observed in similar tropical forests. This is the first report about roots characteristics of forest in the lower sub-tropical area of Dinghushan, Guangdong, China.

Biomass↗
PubMed1985

Root surface measurements of the mandibular first molar.

The root surface area (RSA) per millimeter of root length was determined for 20 extracted mandibular first molars. The molars were cross-sectioned at 1-mm increments, and each section photographed, projected and measured with a calibrated opisometer. The RSA and per cent RSA were calculated for each 1 mm of root length (1-mm section), the root trunk and the individual roots. Also measured was the location of the root separations from the root trunk, the location of the first detectable root concavity, and the prevalence of "intermediate bifurcation ridges" (IBRs). Mean measurements indicated that the greatest RSA per millimeter of root length was 4 to 7 mm apical to the cementoenamel junction (CEJ) in the area of the furcation. Of the total RSA, 48.7% was located in the coronal 6 mm of a root (mean length, 14.4 mm). Root separation occurred 4.0 mm apical to the CEJ with no tooth having a root trunk longer than 6 mm. Buccal and lingual root concavities were first present 0.7 mm and 0.3 mm apical to the CEJ, respectively. Fourteen (70%) of the 20 teeth had IBRs. According to the mean measurements, the mesial root was larger than the distal root by a ratio of 1.0:0.88. Horizontal attachment loss of 6 mm affecting both the buccal and lingual surfaces of the mandibular first molar would have resulted in a through and through (grade 3) furcation involvement of all the teeth studied.

Humans↗
PubMed2000

Root hydraulic conductance: diurnal aquaporin expression and the effects of nutrient stress.

It has been shown that N-, P- and S-deficiencies result in major reductions of root hydraulic conductivity (Lpr) which may lead to lowered stomatal conductance, but the relationship between the two conductance changes is not understood. In a variety of species, Lpr decreases in the early stages of NO3-, H2PO4(2-) and SO4(2-) deprivation. These effects can be reversed in 4-24 h after the deficient nutrient is re-supplied. Diurnal fluctuations of root Lpr have also been found in some species, and an example of this is given for Lotus japonicus. In nutrient-sufficient wheat plants, root Lpr is extremely sensitive to brief treatments with HgCl2; these effects are completely reversible when Hg is removed. The low values of Lpr in N- or P-deprived roots of wheat are not affected by Hg treatments. The properties of plasma membrane (PM) vesicles from wheat roots are also affected by NO3(-)-deprivation of the intact plants. The osmotic permeability of vesicles from N-deprived roots is much lower than that of roots adequately supplied with NO3-, and is insensitive to Hg treatment. In roots of L. japonicus, gene transcripts are found which have a strong homology to those encoding the PIP1 and PIP2 aquaporins of Arabidopsis. There is a very marked diurnal cycle in the abundance of mRNAs of aquaporin gene homologues in roots of L. japonicus. The maxima and minima appear to anticipate the diurnal fluctuations in Lpr by 2-4 h. The temporal similarity between the cycles of the abundance of the mRNAs and root Lpr is most striking. The aquaporin encoded by AtPIP1 is known to have its water permeation blocked by Hg binding. The lack of Hg-sensitivity in roots and PMs from N-deprived roots provides circumstantial evidence that lowered root Lpr may be due to a decrease in either the activity of water channels or their density in the PM. It is concluded that roots are capable, by means completely unknown, of monitoring the nutrient content of the solution in the root apoplasm and of initiating responses that anticipate by hours or days any metabolic disturbances caused by nutrient deficiencies. It is the incoming nutrient supply that is registered as deficient, not the plant's nutrient status. At some point, close to the initiation of these responses, changes in water channel activity may be involved, but the manner in which monitoring of nutrient stress is transduced into an hydraulic response is also unknown.

Aquaporins↗
PubMed2004

[Response of fine roots to soil nutrient spatial heterogeneity].

The spatial heterogeneity is the complexity and variation of systems or their attributes, and the heterogeneity of soil nutrients is ubiquitous in all natural ecosystems. The scale of spatial heterogeneity varies considerably among different ecosystems, from tens of centimeters to hundred meters. Some of the scales can be detected by individual plant. Because the growth of individual plants can be strongly influenced by soil heterogeneity, it follows that the inter-specific competition should also be affected. During the long process of evolution, plants developed various plastic responses with their root system, including morphological, physiological and mycorrhizal plasticity, to maximize the nutrient acquisition from heterogeneous soil resources. Morphological plasticity, an adjustment in root system spatial allocation and architecture in response to spatial heterogeneous distribution of available soil resources, has been most intensively studied, and root proliferation in nutrient rich patches has been certified for many species. The species that do respond may have an increased rate of nutrient uptake, leading to a competitive advantage. Scale and precision are two important features employed in describing the size and foraging behavior of root system. It was hypothesized that scale and precision is negatively related, i. e., the species with high scale of root system tend to be a less precise forager. The outcomes of different research work have been diverse, far from reaching a consensus. Species with high scale are not necessarily less precise in fine root allocation, and vice versa. The proliferation of fine root in enriched micro-sites is species dependent, and also affected by other factors, such as patch attributes (size and nutrients concentration), nutrients, and overall soil fertility. Beside root proliferation in nutrient enriched patches, plants can also adapt themselves to the heterogeneous soil environment by altering other root characteristics such as fine root diameter, branch angle, length, and spatial architecture of root system. Physiological and mycorrhizal plasticity can add some influence on the morphological plasticity to some extent, but they are less studied. Roots located in different patches can quickly regulate their nutrient uptake kinetics within different nutrient patches, and increase overall nutrient uptake. Physiological response may, to certain extent, reduce morphological response, and is meaningful for plant growth on soils with frequently changing spatial and temporal heterogeneity. Mycorrhizal plasticity has been least studied so far. Some researches revealed that mycorrhiza, rather than fine root, proliferated in enriched patches. But, it is not the case with other studies. The proliferation of mycorrhiza within enriched patches is more profitable in term of carbon invest. The effect of fine root proliferation on nutrient uptake is complex, depending on ion mobility and whether or not neighboring plant exists. The influence of root plasticity on the growth of plants is species specific. Some species (sensitive species) gain growth benefit, while others don't. The ability of an individual plant to response to heterogeneous resources has significant effect on its competitive ability and its fate within the community, and eventually shapes the composition and structure of the community.

Adaptation, Physiological↗
PubMed2004

[Significance of senescence study on tree roots and its advances].

Root system is one of the important components of trees, and has some important physiological functions such as nutrient and water absorption, transport and storage, anchoring, and supporting. After tree root systems formed, roots often suffer from nutrient- and water-deficient stress, and thus, their absorption of nutrients and water appears more important. Soil nutrient and water have a great spatiotemporal heterogeneity. As the heterogeneity occurs, trees regulate carbon partitioning to roots, resulting in the senescence or death of some roots of the whole root system. In forestry, the senescence of tree roots is closely related to tree productivity, because there is a close relationship between the senescence of tree roots and the absorption of soil nutrient and water. At ecosystem and global scale, the senescence of tree roots influences the cycling of carbon and nutrients, because roots exhaust a great deal of carbon fixed by source leaves through photosynthesis, and there are great amounts of nutrients in tree roots. The senescence of tree roots is influenced by many environmental factors, biotic (e.g., fungi, bacteria, viruses, small edaphic animals) and abiotic (e.g., water, temperature, soil nutrients, heavy metals). These factors affect the senescence of tree roots by different mechanisms. Although we have much knowledge on the senescence of tree roots and some hypotheses have been proposed, some problems still remain to be resolved, and further experiments are needed to test these hypotheses. Interdisciplinary studies integrating cytology, biochemistry, soil science, and genetics are the prerequisite for rapid advances in understanding the essence of tree root senescence.

Biological Transport↗
PubMed1989

[Anatomical study on the root apex in the maxillary anterior teeth].

This study was undertaken to anatomically investigate the apical portion of root canal. Teeth used in this study were thirty maxillary central incisors, thirty maxillary lateral incisors and thirty maxillary cuspids extracted from patients between the ages of 11 and 73. All of the teeth had periodontal disease, but none had periapical disease. Resorption of the root surface could not be seen with the naked eye. The results obtained were as follows: 1. Deviations of the root apex and the apical foramen. Both of the root apex and apical foramen of the central incisors and cuspids were displaced distolabially from the tooth axis. Those of the lateral incisors were displaced distolingually from the tooth axis. The coincidence between the root apex and apical foramen was found in 16.7 per cent of both the central incisors and the cuspids, and in 6.7 per cent of the lateral incisors. 2. Diameters of the apical foramen and perpendicular distances between the root apex and apical foramen. The labiolingual diameters in the apical foramen of the central incisors, the lateral incisors and the cuspids were 0.504 mm, 0.452 mm and 0.425 mm respectively. Those diameters were larger than the mesiodistal diameters in the maxillary anterior teeth. Both the labiolingual and mesiodistal diameters in the central incisors were the largest. The perpendicular distances between the root apex and the apical foramen of the central incisors, lateral incisors and cuspids were 0.450 mm, 0.440 mm and 0.510 mm respectively. Those in the cuspids were the largest. The apical foramen in the cuspids was located slightly closer to the cervical side. 3. Diameters of the apical constriction and perpendicular distances between the root apex and apical constriction. The apical constriction of the root canal was located in either cementum or dentin. The labiolingual diameters of the root canal in the apical constriction of the central incisors, the lateral incisors and the cuspids were 0.425 mm, 0.369 mm and 0.425 mm respectively. The root canal labiolingual diameters in the maxillary anterior teeth was approximately 0.050 mm larger than mesiodistal diameters. The shapes of the root canal in the apical constriction were mostly the circular, oval and ovoid, while a few irregular shapes were observed. The perpendicular distances between the root apex and the apical constriction of the root canal in the central incisors, the lateral incisors and the cuspids were 0.863 mm, 0.825 mm and 1.010 mm respectively. 4. The stricture ratio of diameter between the apical foramen and the apical constriction of the root canal.(ABSTRACT TRUNCATED AT 400 WORDS)

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