Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “root”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,261 records · Page 70Linked to original sources
PubMed2003

Role of manganese in low-pH-induced root hair formation in Lactuca sativa cv. Grand Rapids seedlings.

Root hair formation is induced by low pH in lettuce ( Lactuca sativa L. cv. Grand Rapids) seedlings cultured in mineral medium. The role of mineral concentrations in this phenomenon was investigated, especially for manganese. When lettuce seedlings were cultured in media that were deficient in calcium (Ca), manganese (Mn), boron (B) or molybdenum (Mo), morphological changes were induced in roots. Deficiency of other nutrients had little effect on root hair formation. Ca or B deficiency inhibited the growth of the main root and the formation of root hairs, regardless of pH. Mn or Mo deficiency increased root hair formation at pH 6 and suppressed main root growth slightly. In contrast, increasing the Mn concentration suppressed low-pH-induced root hair formation. The Mn content of roots grown at pH 4 was only about 15% of that at pH 6. In contrast, the Mo content of roots grown at low pH was about six times that of roots grown at neutral pH. These results suggest that root hair formation induced by low pH is at least partly mediated by decreased Mn uptake in root cells.

Boron↗
PubMed1986

Spinal entry route for ventral root afferent fibers in the cat.

Twelve anesthetized and paralyzed cats were used to study the spinal entry routes of ventral root afferent fibers. In all animals, the spinal cord was transected at two different levels, L5 and S2. The L5 through S2 dorsal roots were cut bilaterally, making spinal cord segments L5-S2 neurally isolated from the body except for the L5-S2 ventral roots. From this preparation, a powerful excitation of the discharge rate of motor neurons and dorsal horn cells within the isolated spinal segments was observed after intraarterial injection of bradykinin (50 micrograms in 0.5 ml saline). This excitation of the spinal neurons can be considered the most convincing evidence of the potential physiologic role of the ventral root afferent fibers entering the spinal cord directly through the ventral root, because the apparent route of neuronal input from the periphery is through the ventral roots. However, additional control experiments conducted in the present study showed that the excitation persisted even after cutting all ventral roots within the isolated spinal segments, indicating that excitation was not mediated by the ventral roots. Furthermore, direct application of bradykinin on the dorsal surface of the spinal cord also increased the motoneuronal discharge rate, suggesting that excitation of spinal neurons produced by intraarterial injection of bradykinin is due to a direct action of bradykinin on the spinal cord. Thus, we provided an alternate explanation for the most convincing evidence indicating that physiologically important ventral root afferent fibers enter the spinal cord directly through the ventral root. Based on existing experimental evidence, it is likely that the majority of physiologically active ventral root afferent fibers travel distally toward the dorsal root ganglion and then enter the spinal cord through the dorsal root.

Action Potentials↗
PubMed1992

The role of calcium in the regulation of hormone transport in gravistimulated roots.

Prior research has shown that gravistimulation induces preferential movement of calcium toward the lower side of the tips of maize roots and that roots depleted of calcium show impaired gravitropism. To further investigate the role of calcium in root gravitropism, we examined the effects of calcium on auxin movement in both vertical and gravistimulated roots of maize. Longitudinal movement of auxin was basipetally polar in intact roots but acropetally polar in decapped roots. Treatment of the root tip with calcium increased basipetal auxin movement in both intact and decapped roots. Gravistimulation induced asymmetric auxin movement toward the lower side of the root tip. Both asymmetric auxin movement and gravicurvature were inhibited by treatment of the root tip with auxin transport inhibitors or with EGTA. The results indicate that there is a close correlation between curvature and gravity-induced asymmetric auxin movement across the root cap. Since gravistimulation causes calcium movement toward the lower side of the root tip, our observation that calcium promotes basipetal auxin movement supports the idea that gravity-induced calcium asymmetry is a key step linking gravistimulation to the establishment of auxin asymmetry during root gravitropism.

Biological Transport↗
PubMed1994

Dye leakage of four root end filling materials: effects of blood contamination.

The purpose of this study was to compare the amount of dye leakage (in the presence versus absence of blood) in root end cavities filled with amalgam, Super EBA, IRM, and a mineral trioxide aggregate. After removing the anatomical crowns of 90 extracted human teeth, their roots were instrumented and obturated. Except for their apical 2 mm, the root surfaces were sealed with nail polish. After removal of the apical 2 to 3 mm of each root, a standardized root end cavity was prepared. Five root ends were filled with gutta-percha and no sealer, and another five root ends were filled with sticky wax. These served as positive and negative controls, respectively. The remaining 80 roots were divided into four equal groups and filled with the test materials. For each material, half of the root end cavities were dried prior to placing the filling material. The remaining half were filled after they were contaminated with blood. All 90 roots were then immediately placed in 1% methylene blue dye for 72 h. Finally, the roots were split and linear dye penetration was measured and statistically analyzed (analysis of variance). Presence or absence of blood had no significant effect on the amount of dye leakage. However, the results showed that there was a significant leakage difference between the root end filling materials (p < 0.0001). Mineral trioxide aggregate leaked significantly less than other materials tested with or without blood contamination of the root end cavities.

Aluminum Compounds↗
PubMed1997

Use of a lux-based procedure to rapidly visualize root colonisation by Pseudomonas fluorescens in the wheat rhizosphere.

The bioluminescently marked Pseudomonas fluorescens strain 5RL, has been used previously to follow colonisation of soy bean roots (De Weger et al. [1991] Appl. Environ. Microbiol. 57:36-41). In the present paper the method has been further developed and optimized for wheat roots and it is used to get a quick overview of the colonisation patterns of many different root systems at the same time. Colonisation was followed on wheat plants grown in our gnotobiotic sand system (Simons et al., 1996. Mol Plant Microbe Interact 9: 600-607) and the following results were obtained. (i) A spatio-temporal analysis of the colonisation of wheat roots showed that 4 days after planting the highest bacterial activity was observed at the upper part of the root. After 6 days the high bacterial activity at the upper part was further increased, whereas spot-like activities were observed on the lower root parts, possibly due to micro-colonies. (ii) Bacterial mutations causing lack of motility or auxotrophy for amino acids resulted in impaired colonisation of the lower root parts, indicating that motility and prototrophy for the involved amino acid(s) are important factors for wheat root colonisation by strain 5RL. (iii) Coinoculation of strain 5RL with other wild type Pseudomonas strains on the root influenced the colonisation pattern observed for strain 5RL. Colonisation was not visually affected when the competing strain was a poor root coloniser, but was severely reduced when the competing strain was a good root coloniser. The results show that the spatio-temporal colonisation of wheat root by P. fluorescens strain 5RL and derivatives is similar to that of strain WCS365 on tomato. The advantage of the use of lux-marked strains is that the results are obtained much quicker than when conventional methods are used and that the result is supplied as an image of the colonisation pattern of many different roots.

Biosensing Techniques↗
PubMed2004

Production and analysis of organic acids in hairy-root cultures of Isatis indigotica Fort. (indigo woad).

Hairy roots were induced from both cotyledon and hypocotyl explants of Isatis indigotica Fort. (indigo woad) through transformation with Agrobaterium rhizogenes strain A4, R1601 and ATCC15834. The results showed that the cotyledons were the preferred explants to hypocotyls and A4 was the most suitable A. rhizogenes strain for the transformation and induction of hairy roots of I. indigotica. High-voltage paper electrophoresis (HVPE) analysis demonstrated the production of mannopine in hairy roots and confirmed the successful transfer of Ri T-DNA (root-inducing transferred DNA) of A. rhizogenes into the I. indigotica genome. Five organic acids, namely CPQ [3-(2-carboxyphenol)-4(3 H )-quinazolinone], syringic acid, salicylic acid, benzoic acid and 2-aminobenzoic acid, which were considered as main antiviral components of I. indigotica, were detected in natural roots, hairy roots and liquid media with high-performance capillary electrophoresis. The results showed CPQ production in hairy roots was significantly higher than that in natural roots. Our results also revealed that all the five organic acids could be excreted from hairy roots into liquid media, and the concentrations of organic acids in the liquid media paralleled those in hairy roots. The hairy roots of I. indigotica grew fast and showed an S-shaped growth curve that reached its apex on the day 24 of culture with a 20-fold increase in fresh weight compared with the starting inoculums. The accumulation of the two organic acids CPQ and syringic acid in liquid media paralleled the growth of hairy roots. MS [Murashige, T. and Skoog, F. (1962) Physiol. Plant. 15, 473-497] medium or half-strength MS medium supplemented with 30 g/l maltose was found to be best for hairy-root culture and accumulation of CPQ.

Benzoic Acid↗
PubMed2005

Nitrate and glutamate sensing by plant roots.

The architecture of a root system plays a major role in determining how efficiently a plant can capture water and nutrients from the soil. Growth occurs at the root tips and the process of exploring the soil volume depends on the behaviour of large numbers of individual root tips at different orders of branching. Each root tip is equipped with a battery of sensory mechanisms that enable it to respond to a range of environmental signals, including nutrients, water potential, light, gravity and touch. We have previously identified a MADS (MCM1, agamous, deficiens and SRF) box gene (ANR1) in Arabidopsis thaliana that is involved in modulating the rate of lateral root growth in response to changes in the external NO(3)(-) supply. Transgenic plants have been generated in which a constitutively expressed ANR1 protein can be post-translationally activated by treatment with dexamethasone (DEX). When roots of these lines are treated with DEX, lateral root growth is markedly stimulated but there is no effect on primary root growth, suggesting that one or more components of the regulatory pathway that operate in conjunction with ANR1 in lateral roots may be absent in the primary root tip. We have recently observed some very specific effects of low concentrations of glutamate on root growth, resulting in significant changes in root architecture. Experimental evidence suggests that this response involves the sensing of extracellular glutamate by root tip cells. We are currently investigating the possible role of plant ionotropic glutamate receptors in this sensory mechanism.

Glutamates↗
PubMed1997

The effect of root canal morphology on canal shape following instrumentation using different techniques.

The objective of this study was to evaluate the shaping characteristics of different root canal instruments in teeth with different root canal forms. A total of 420 extracted human roots were embedded in resin blocks. The embedded roots were divided into three groups, i.e., roots with (i) straight (I form), (ii) apically curved (J form), and (iii) entirely curved canals (C form) with reference to the Schneider's angle and the length of the radius of arc of the curvature of the root canals. Each of the three groups containing 140 roots were randomly divided into seven subgroups prior to preparation. The canals were enlarged manually with traditional and flexible hand instruments, three different engine driven instruments and sonically and ultrasonically powered instruments. The shortcomings of the seven preparation methods were assessed by superimposition of projected radiographs taken in bucco-lingual and mesio-distal views before and after preparation. Results showed that observation of perforation, incidence of elbow and of asymmetrical preparation of the root canals depended on root canal configuration. It was striking that the coronal transposition of the apical stop, uneven wall contour, ledge formation and incidence of zip were independent of root canal morphology. Evaluation of data of asymmetry of preparation (canal transposition) revealed significant differences (p < 0.05). Asymmetry of preparation was the most frequent aberration of the prepared root canals and it was possible to study it with precision. It was concluded that this measurement should be a priority for future instrument testing. The shaping characteristics of hand and engine driven instruments was modified by root canal morphology, but that of sonic and ultrasonic instruments was less dependent on the original anatomical form of root canals.

Analysis of Variance↗
PubMed1999

A comparison in vitro of fibroblast attachment to resected root-ends.

AIM: The aim of this study was to investigate the effect of surface morphology of root ends resected with various bur configurations on fibroblast attachment. METHODOLOGY: Seventy-two human single-rooted teeth were collected and decoronated. The root canals were instrumented, and then obturated with thermoplasticized gutta-percha using AH-26 as the sealer. The roots were randomly divided into eight different groups, and apical root-end resections were performed using eight different instruments, which included high and low speed burs and a scalpel blade. After each root was resected, the surface area of the root end was measured. Cultured human periodontal ligament fibroblasts were radiolabelled and then allowed to attach, in vitro, to the root-ends. Cell attachment to the resected root-ends was determined by counting in a liquid scintillation system and expressed as the number of decays per min/mm2 (DPM/mm2) of root surface. RESULTS: There was no significant difference in fibroblast attachment to the root-ends prepared with various instruments. CONCLUSIONS: These findings indicate that the choice of instrument for root-end resection has little influence on the initial attachment of fibroblasts, and thus may have little effect on healing following root-end resection.

Analysis of Variance↗
PubMed2001

Root canal systems of the mandibular and maxillary first permanent molar teeth of south Asian Pakistanis.

AIM: The purpose of the present ex vivo study was to investigate variations in the root canal systems of mandibular and maxillary first permanent molar teeth of South Asian Pakistanis. METHODOLOGY: The root canal systems of a sample of 30 mandibular and 30 maxillary first permanent molar teeth extracted from South Asian Pakistanis were studied using a clearing technique. RESULTS: The mesial roots of the mandibular molar teeth typically presented with two canals (97%) of type II, IV or VI configuration. The distal roots of these teeth presented with a single canal (50%) of type I or V configuration or with two canals (50%) of type II, IV or VI. The prevalence of four root canals in two-rooted mandibular first permanent molar teeth was 47%. In maxillary molar teeth the mesial roots with a single canal (47%) were type I or type V; those with two canals (53%) were type II, IV or type VI. The distal and palatal roots that presented as a single canal (100%) were type I or type V configuration. The prevalence of four root canals in three-rooted maxillary first permanent molar teeth was 53%. CONCLUSION: It is concluded that four root canals in mandibular and maxillary first permanent molar teeth of South Asian Pakistanis is a common occurrence. The distribution of the different configurations of root canal systems in this population differed from that in Caucasian groups, suggesting that variations in root canal systems may be attributed to racial divergence.

Carbon↗
PubMed1997

Cytoplasmic free calcium distributions during the development of root hairs of Arabidopsis thaliana.

In this study, confocal ratio analysis was used to image the relationship between cytoplasmic free calcium concentration ([Ca2+]c) and the development of root hairs of Arabidopsis thaliana. Although a localized change in [Ca2+]c that preceded or predicted the site of root hair initiation could not be detected, once initiated the majority of emerging root hairs showed an elevated [Ca2+]c (> 1 microM) in their apical cytoplasm, compared with 100-200 nM in the rest of the cell. These emerging root hairs then moved into a 3-5 h phase of sustained elongation during which they showed variable growth rates. Root hairs that were rapidly elongating exhibited a highly localized, elevated [Ca2+]c at the tip. Non-growing root hairs did not exhibit the [Ca2+]c gradient. The rhd-2 mutant, which is defective in sustained root hair growth, showed an altered [Ca2+]c distribution compared with wild-type. These results implicate [Ca2+]c in regulating the tip growth process. Treatment of elongating wild-type root hairs with the Ca2+ channel blocker verapamil (50 microM) caused dissipation of the elevated [Ca2+]c at the tip and cessation of growth, suggesting a requirement for Ca2+ channel activity at the root hair tip to maintain growth. Manganese treatment also preferentially quenched Indo-1 fluorescence in the apical cytoplasm of the root hair. As manganese is thought to enter cells through Ca(2+)-permeable channels, this result also suggests increased Ca2+ channel activity at the tip of the growing hair. Taken together, these data suggest that although Ca2+ does not trigger the initiation of root hairs, Ca2+ influx at the tip of the root hair leads to an elevated [Ca2+]c that may be required to sustain root hair elongation.

Arabidopsis↗
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↗
PubMed2006

Rates of root and organism growth, soil conditions, and temporal and spatial development of the rhizosphere.

BACKGROUND: Roots growing in soil encounter physical, chemical and biological environments that influence their rhizospheres and affect plant growth. Exudates from roots can stimulate or inhibit soil organisms that may release nutrients, infect the root, or modify plant growth via signals. These rhizosphere processes are poorly understood in field conditions. SCOPE AND AIMS: We characterize roots and their rhizospheres and rates of growth in units of distance and time so that interactions with soil organisms can be better understood in field conditions. We review: (1) distances between components of the soil, including dead roots remnant from previous plants, and the distances between new roots, their rhizospheres and soil components; (2) characteristic times (distance(2)/diffusivity) for solutes to travel distances between roots and responsive soil organisms; (3) rates of movement and growth of soil organisms; (4) rates of extension of roots, and how these relate to the rates of anatomical and biochemical ageing of root tissues and the development of the rhizosphere within the soil profile; and (5) numbers of micro-organisms in the rhizosphere and the dependence on the site of attachment to the growing tip. We consider temporal and spatial variation within the rhizosphere to understand the distribution of bacteria and fungi on roots in hard, unploughed soil, and the activities of organisms in the overlapping rhizospheres of living and dead roots clustered in gaps in most field soils. CONCLUSIONS: Rhizosphere distances, characteristic times for solute diffusion, and rates of root and organism growth must be considered to understand rhizosphere development. Many values used in our analysis were estimates. The paucity of reliable data underlines the rudimentary state of our knowledge of root-organism interactions in the field.

Diffusion↗
PubMed2003

Instrumental methods for studies of structure and function of root systems of large trees.

New methods using different physical principles have been successfully applied in studies of root systems of large trees. The ground-penetrating radar technique provides 3D images of coarse roots (starting with a diameter of about 20 mm) from the soil surface down to a depth of several metres. This can even be done under layers of undisturbed materials such as concrete, asphalt and water. Fine roots cannot be visualized by this method, but the total rooted volume of soil can be determined. The differential electric conductance method has been used for fast measurement of conducting (absorbing) root surfaces. However, more testing is needed. Both these methods are non-invasive. The results can be verified by an almost harmless excavation of whole root systems, including fine roots, using the ultrasonic air-stream (air-spade) method. This method is suitable for all studies, as well as practical operations on roots or objects in their vicinity, where a gentle approach is required. Sap flow measurements on their own or in tandem with soil moisture monitoring play a leading role in studying root function and hydraulic redistribution of flow in the soil. The water absorption function of roots can be studied by measuring sap flow on individual root branches directly (as on crown branches) and also indirectly, by measuring the radial pattern of sap flow in different sapwood depths at the base of a stem. Root zone architecture can also be estimated indirectly by studying its functionality. The heat field deformation method with multi-point sensors has been found to be very convenient for this purpose. A combination of several such methods is recommended whenever possible, in order to obtain detailed information about the root systems of trees.

Biological Transport↗
PubMed2005

Gating of aquaporins by low temperature in roots of chilling-sensitive cucumber and chilling-tolerant figleaf gourd.

Effects of low temperature (8 degrees C) on the hydraulic conductivity of young roots of a chilling-sensitive (cucumber, Cucumis sativus L.) and a chilling-resistant (figleaf gourd, Cucurbita ficifolia Bouche) crop have been measured at the levels of whole root systems (root hydraulic conductivity, Lp(r)) and of individual cortical cells (cell hydraulic conductivity, Lp). Exposure of roots to low temperature (LRT) for up to 6 d caused a stronger suberization of the endodermis in cucumber compared with figleaf gourd, but no development of exodermal Casparian bands in either species. Changes in anatomy after 6 d of LRT treatment corresponded with a reduction in hydrostatic root Lp(r) of cucumber roots by a factor of 24, and by a factor of 2 in figleaf gourd. In figleaf gourd, there was a reduction only in hydrostatic Lp(r) but not in osmotic Lp(r) suggesting that the activity of water channels was not much affected by LRT treatment in this species. Changes in cell Lp in response to chilling and recovery were similar to the root levels, although they were more intense at the root level. Activation energies (E(a)) and Q10 of water flow as measured at the cell level were high in cucumber (E(a)=109+/-13 kJ mol(-1); Q(10)=4.8+/-0.7; n=6-10 cells), but small in figleaf gourd (E(a)=11+/-2 kJ mol(-1); Q10=1.2+/-0.1; n=6-10 cells). Roots of figleaf gourd recovered better from LRT treatment than those of cucumber. In figleaf gourd, recovery (at both the root and cell level) often resulted in Lp and Lp(r) values which were even bigger than the original, i.e. there was an overshoot in hydraulic conductivity. These effects were larger for osmotic (representing the cell-to-cell passage of water) than for hydrostatic Lp(r). After a short-term (1 d) exposure to 8 degrees C followed by 1 d at 20 degrees C, hydrostatic Lp(r) of cucumber nearly recovered and that of figleaf gourd still remained higher due to the overshoot. By contrast, osmotic Lp(r) and cell Lp in both species remained high by a factor of 3 compared with the control, possibly due to an increased activity of water channels. After preconditioning of roots at LRT, increased hydraulic conductivity was completely inhibited by HgCl2 at both the root and cell levels. Different from figleaf gourd, recovery from chilling was not complete in cucumber after longer exposure to LRT. It is concluded that at LRT, both changes in the activity of aquaporins (AQPs) and alterations of root anatomy determine the water uptake in both species. The high temperature dependence of cell Lp in cucumber suggests conformational changes of AQPs during LRT treatment which result in channel closure and in a strong gating of AQP activity by low temperature. This mechanism is thought to be different from that in figleaf gourd where AQPs reacted in the conventional way, i.e. low temperature affected the mobility of water molecules in AQPs rather than their open/closed state, and Q(10) was low.

Adaptation, Physiological↗
PubMed2005

Root responses to soil physical conditions; growth dynamics from field to cell.

Root growth in the field is often slowed by a combination of soil physical stresses, including mechanical impedance, water stress, and oxygen deficiency. The stresses operating may vary continually, depending on the location of the root in the soil profile, the prevailing soil water conditions, and the degree to which the soil has been compacted. The dynamics of root growth responses are considered in this paper, together with the cellular responses that underlie them. Certain root responses facilitate elongation in hard soil, for example, increased sloughing of border cells and exudation from the root cap decreases friction; and thickening of the root relieves stress in front of the root apex and decreases buckling. Whole root systems may also grow preferentially in loose versus dense soil, but this response depends on genotype and the spatial arrangement of loose and compact soil with respect to the main root axes. Decreased root elongation is often accompanied by a decrease in both cell flux and axial cell extension, and recent computer-based models are increasing our understanding of these processes. In the case of mechanical impedance, large changes in cell shape occur, giving rise to shorter fatter cells. There is still uncertainty about many aspects of this response, including the changes in cell walls that control axial versus radial extension, and the degree to which the epidermis, cortex, and stele control root elongation. Optical flow techniques enable tracking of root surfaces with time to yield estimates of two-dimensional velocity fields. It is demonstrated that these techniques can be applied successfully to time-lapse sequences of confocal microscope images of living roots, in order to determine velocity fields and strain rates of groups of cells. In combination with new molecular approaches this provides a promising way of investigating and modelling the mechanisms controlling growth perturbations in response to environmental stresses.

Acclimatization↗
PubMed2006

Root exudation from Hordeum vulgare in response to localized nitrate supply.

Root proliferation as a response to exploit zones of nutrient enrichment in soil has been demonstrated for a wide range of plant species. However, the effectiveness of this as a strategy to acquire nutrients is also dependent on interactions with the soil microbial community. Specifically, C-flow from roots modifies microbial activity and probably the balance between nutrient mineralization and immobilization processes in the rhizosphere. In this study, near-natural abundance 13C-labelling and gene-reporter methods were applied to determine the effects of uneven nitrate supply to roots of Hordeum vulgare on assimilate partitioning and root exudation. Plants were initially grown in uniform nitrate supply in split-root, sand microcosms after which one treatment continued to receive uniform supply, and the other received nitrate to one root compartment only. At the time of imposing the treatments, the CO2 supplied to the plants was switched to a cylinder source, providing a distinct delta13C-signature and allowing the fate of new assimilate within the plants to be determined. The labelling approach allowed quantification of the expected preferential allocation of new C-assimilate to roots in enriched nitrate, prior to any measurable effect on whole biomass or root architecture. Biosensor (lux-marked Pseudomonas fluorescens 10586 pUCD607) bioluminescence, quantified spatially by CCD imaging, demonstrated that root exudation was significantly increased for roots in enriched nitrate. This response of root exudation, being primarily associated with root apices and concurrent with enhanced assimilate supply, strongly suggests that C-flow from roots is an integral component of the proliferation response to nitrate.

Biosensing Techniques↗
PubMed2005

Cytokinin receptors are required for normal development of auxin-transporting vascular tissues in the hypocotyl but not in adventitious roots.

Plants alter the architecture of their root systems to adapt to the environment by modulating post-embryonic (lateral and adventitious) root formation and growth. To understand better the genetic basis of this regulation, we screened ethylmethane sulfonate-mutagenized lines of Arabidopsis thaliana for adventitious rooting mutants. One mutant showed retardation of the primary root growth, no production of lateral roots and enhanced formation of adventitious roots. Mapping and genetic complementation revealed that this mutant named wooden leg-3 (wol-3) was an allele of ARABIDOPSIS HISTIDINE KINASE 4 (AHK4), a locus known to encode a cytokinin receptor. Although the vascular system of the primary root and hypocotyl in the wol-3 mutant was aborted, that of the adventitious roots was normally developed. In the hypocotyl of the wol-3 mutant, auxin signals accumulated around the aborted vascular system. The application of auxin to primary roots induced lateral root formation in the wol-3 mutant. Transport of radiolabeled auxin from the top of the hypocotyl to the primary root was inhibited in wol-3. Although only a single amino acid alteration had occurred in AHK4, the root morphology in the wol-3 mutant was quite similar to that in the ahk2 ahk3 ahk4 triple mutant, which is a loss-of-function mutant of the three cytokinin receptors. This implies that the functional disturbance of AHK4 affects the function of the other receptors. Our results suggest that cytokinin receptors are necessary for the formation of auxin-transporting vascular tissues in the hypocotyl, but not in adventitious roots.

Alleles↗