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Root Tips (root + tip)

Distribution by Scientific Domains

Life Sciences	77%
Earth and Environmental Science	5%

Distribution within Life Sciences

Plant Science	75%
Microbial Ecology	10%
4 Other Subdomains	15%

Selected Abstracts

Two similar enhanced root-colonizing Pseudomonas strains differ largely in their colonization strategies of avocado roots and Rosellinia necatrix hyphae

ENVIRONMENTAL MICROBIOLOGY, Issue 12 2008
Clara Pliego
Summary Pseudomonas alcaligenes AVO73 and Pseudomonas pseudoalcaligenes AVO110 were selected previously as efficient avocado root tip colonizers, displaying in vitro antagonism towards Rosellinia necatrix, causal agent of avocado white root rot. Despite the higher number of antagonistic properties shown in vitro by AVO73, only AVO110 demonstrated significant protection against avocado white root rot. As both strains are enhanced root colonizers, and as colonization is crucial for the most likely biocontrol mechanisms used by these strains, namely production of non-antibiotic antifungal compounds and competition for nutrients and niches, we decided to compare the interactions of the bacterial strains with avocado roots as well as with R. necatrix hyphae. The results indicate that strain AVO110 is superior in biocontrol trait swimming motility and establishes on the root tip of avocado plants faster than AVO73. Visualization studies, using Gfp-labelled derivatives of these strains, showed that AVO110, in contrast to AVO73, colonizes intercellular crevices between neighbouring plant root epidermal cells, a microhabitat of enhanced exudation. Moreover, AVO110, but not AVO73, also colonizes root wounds, described to be preferential penetration sites for R. necatrix infection. This result strongly suggests that AVO110 meets, and can attack, the pathogen on the root. Finally, when co-inoculated with the pathogen, AVO110 utilizes hyphal exudates more efficiently for proliferation than AVO73 does, and colonizes the hyphae more abundantly than AVO73. We conclude that the differences between the strains in colonization levels and strategies are likely to contribute to, and even can explain, the difference in disease-controlling abilities between the strains. This is the first report that shows that two similar bacterial strains, selected by their ability to colonize avocado root, use strongly different root colonization strategies and suggests that in addition to the total bacterial root colonization level, the sites occupied on the root are important for biocontrol. [source]

Simultaneous detection of the establishment of seed-inoculated Pseudomonas fluorescens strain DR54 and native soil bacteria on sugar beet root surfaces using fluorescence antibody and in situ hybridization techniques

FEMS MICROBIOLOGY ECOLOGY, Issue 1 2000
Peter Stephensen Lübeck
Abstract Colonization at sugar beet root surfaces by seedling-inoculated biocontrol strain Pseudomonas fluorescens DR54 and native soil bacteria was followed over a period of 3 weeks using a combination of immunofluorescence (DR54-targeting specific antibody) and fluorescence in situ hybridization (rRNA-targeting Eubacteria EUB338 probe) techniques with confocal laser scanning microscopy. The dual staining protocol allowed cellular activity (ribosomal number) to be recorded in both single cells and microcolonies of strain DR54 during establishment on the root. After 2 days, the population density of strain DR54 reached a constant level at the root basis. From this time, however, high cellular activity was only found in few bacteria located as single cells, whereas all microcolony-forming cells occurring in aggregates were still active. In contrast, a low density of strain DR54 was observed at the root tip, but here many of the bacteria located as single cells were active. The native population of soil bacteria, comprising a diverse assembly of morphologically different forms and size classes, initiated colonization at the root basis only after 2 days of incubation. Hence the dual staining protocol allowed direct microscopic studies of early root colonization by both inoculant and native soil bacteria, including their differentiation into active and non-active cells and into single or microcolony-forming cells. [source]

Limitations of previously published systematic reviews evaluating the outcome of endodontic treatment

INTERNATIONAL ENDODONTIC JOURNAL, Issue 8 2009
M-K. Wu
Abstract The aim of this work was to identify the limitations of previously published systematic reviews evaluating the outcome of root canal treatment. Traditionally, periapical radiography has been used to assess the outcome of root canal treatment with the absence of a periapical radiolucency being considered a confirmation of a healthy periapex. However, a high percentage of cases confirmed as healthy by radiographs revealed apical periodontitis on cone beam computed tomography (CBCT) and by histology. In teeth, where reduced size of the existing radiolucency was diagnosed by radiographs and considered to represent periapical healing, enlargement of the lesion was frequently confirmed by CBCT. In clinical studies, two additional factors may have further contributed to the overestimation of successful outcomes after root canal treatment: (i) extractions and re-treatments were rarely recorded as failures; and (ii) the recall rate was often lower than 50%. The periapical index (PAI), frequently used for determination of success, was based on radiographic and histological findings in the periapical region of maxillary incisors. The validity of using PAI for all tooth positions might be questionable, as the thickness of the cortical bone and the position of the root tip in relation with the cortex vary with tooth position. In conclusion, the serious limitations of longitudinal clinical studies restrict the correct interpretation of root canal treatment outcomes. Systematic reviews reporting the success rates of root canal treatment without referring to these limitations may mislead readers. The outcomes of root canal treatment should be re-evaluated in long-term longitudinal studies using CBCT and stricter evaluation criteria. [source]

An investigation into the relationship between apical root Impedance and canal anatomy

INTERNATIONAL ENDODONTIC JOURNAL, Issue 9 2008
S. M. Ardeshna
Aim, To investigate a possible relationship between apical root impedance and canal anatomy. Methodology, Twenty-three roots from human extracted teeth (mostly single rooted but also from molars) with different apical anatomy were selected. The apical anatomy was initially classified by staining the root tip to identify number of canal exits; after impedance measurements, the anatomy was confirmed by staining and clearing the dentine. The roots were divided into two groups; 12 had simple (S) anatomy (Vertucci type 1 with a single exit) and 11 had complex (C) anatomy (various Vertucci canal types with multiple exist). Impedance measurements were taken using a frequency response analyser at seven levels in the root (0.0, 0.5, 1.0, 2.0, 3.0, 4.0 and 5.0 mm short of the apical terminus) at 14 frequencies ranging from 1120 to 100 000 Hz. Care was taken to control the temperature and other variables that could confound measurement accuracy. The impedance characteristics of individual roots were compared with 37 equivalent circuits (based on a pool created from a previous study); the best fitting equivalent circuit was selected. The equivalent circuits were used as the single outcome measure describing the impedance characteristics and correlated with the canal anatomy (S/C). Generalized estimating equations were used to perform logistic regression to analyse the data. Results, Canal anatomy had a significant (P = 0.046) effect on the equivalent circuit model. One circuit (model 10) was found to be the commonest and occurred significantly more commonly in the simple canals. The odds of prevalence of circuit model 10 were 2.2 times (odds ratio 2.17, 95% confidence interval 1.01,4.63) higher in canals with simple anatomy compared with canals with complex anatomy. Conclusions, Canal anatomy had a significant effect on the equivalent circuit describing its impedance characteristics. It should be possible to use impedance spectroscopy to clinically predict and image apical canal complexities. [source]

Ex vivo study of the adhesion of an epoxy-based sealer to human dentine submitted to irradiation with Er : YAG and Nd : YAG lasers

INTERNATIONAL ENDODONTIC JOURNAL, Issue 12 2005
M. D. Sousa-Neto
Abstract Aim, To evaluate the adhesion of an epoxy-based sealer to human dentine submitted to irradiation with Er : YAG or Nd : YAG laser at various parameters. Methodology, Ninety maxillary canine teeth were sectioned transversely at the cemento-enamel junction and at the root tip to leave an 8-mm-long cylinder. The tooth specimen was centred in a metallic ring (16 mm diameter and 8 mm height) and embedded in acrylic resin. The root canals were prepared using a low-speed handpiece and a conical diamond bur, which was attached to a paralleling device. This bur was lowered to a depth previously determined by a silicone stop. Specimens were divided into nine groups: group I, dentine was treated with 2 mL of 17% EDTAC for 5 min. Groups II,V were irradiated with Er : YAG laser at the following parameters: group II , 8 Hz and 200 mJ input (120 mJ output); group III , 8 Hz and 400 mJ input (240 mJ output); group IV , 16 Hz and 200 mJ input (120 mJ output); group V , 16 Hz and 400 mJ input (240 mJ output). Groups VI,IX were irradiated with Nd : YAG laser at the following parameters: group VI , 10 Hz and 1 W input (0.4 W output); group VII , 10 Hz and 2 W input (0.8 W output); group VIII , 15 Hz and 1 W input (0.4 W output); group IX , 15 Hz and 2 W input (0.8 W output). The root canals were filled with an epoxy-based root canal sealer and submitted to a push-out test. Results, Statistical analysis showed significant differences (P < 0.01) between Er : YAG and Nd : YAG laser treatments at the higher frequencies compared with 17% EDTAC. Greater adhesion values were obtained for groups IV and V (Er : YAG laser) and groups VIII and IX (Nd : YAG laser), which were statistically different from groups II and III (Er : YAG laser) and groups VI and VII (Nd : YAG laser). Treatment with only 17% EDTAC had the lowest adhesion values. Conclusions, An increase in frequency, independent of power settings, of the lasers used in this study increased adhesion of an epoxy-based root canal sealer. [source]

Resolution of persistent periapical infection by endodontic surgery

INTERNATIONAL ENDODONTIC JOURNAL, Issue 1 2004
F. B. A. Ferreira
Abstract Aim, To examine the surfaces of a root tip removed during surgical endodontic treatment for the presence of microorganisms. Summary, The present clinical case illustrates an endodontic retreatment of a maxillary premolar tooth with a fistula and periapical reaction. The case was under treatment for 1 year, during which an intracanal medicament was replaced several times. As the lesion did not decrease and exudate was persistent through the fistula and root canal, root end resection with root end filling was performed. Microbiological samples were collected from the fistula, where Propionibacterium acnes, a species associated with endodontic failures, was detected by appropriate anaerobic technique. The resected root apex was observed by scanning electron microscopy (SEM), which revealed cocci and fungal forms surrounding one of the foramina. After 12 months, the periapical lesion had reduced. Key learning points ,,Persistent extraradicular infections are not affected by the action of antimicrobial agents such as irrigants and medicaments used during root canal treatment. ,,Apical surgery is a suitable alternative for definitive removal of an established refractory infection, promoting repair of difficult cases. [source]

Gravisensitivity and automorphogenesis of lentil seedling roots grown on board the International Space Station

PHYSIOLOGIA PLANTARUM, Issue 1 2008
Dominique Driss-Ecole
The GRAVI-1 experiment was brought on board the International Space Station by Discovery (December 2006) and carried out in January 2007 in the European Modular Cultivation System facility. For the first run of this experiment, lentil seedlings were hydrated and grown in microgravity for 15 h and then subjected for 13 h 40 min to centrifugal accelerations ranging from 0.29 × 10,2 g to 0.99 × 10,2 g. During the second run, seedlings were grown either for 30 h 30 min in microgravity (this sample was the control) or for 21 h 30 min and then subjected to centrifugal accelerations ranging from 1.2 × 10,2 g to 2.0 × 10,2 g for 9 h. In both cases, root orientation and root curvature were followed by time-lapse photography. Still images were downlinked in near real time to ground Norwegian User Support and Operations Center during the experiment. The position of the root tip and the root curvature were analyzed as a function of time. It has been shown that in microgravity, the embryonic root curved strongly away from the cotyledons (automorphogenesis) and then straightened out slowly from 17 to 30 h following hydration (autotropism). Because of the autotropic straightening of roots in microgravity, their tip was oriented at an angle close to the optimal angle of curvature (120°,135°) for a period of 2 h during centrifugation. Moreover, it has been demonstrated that lentil roots grown in microgravity before stimulation were more sensitive than roots grown in 1 g. In these conditions, the threshold acceleration perceived by these organs was found to be between 0 and 2.0 × 10,3 g and estimated punctually at 1.4 × 10,5 g by using the hyperbolic model for fitting the experimental data and by assuming that autotropism had no or little impact on the gravitropic response. Gravisensing by statoliths should be possible at such a low level of acceleration because the actomyosin system could provide the necessary work to overcome the activation energy for gravisensing. [source]

Effect of boron on the expression of aluminium toxicity in Phaseolus vulgaris

PHYSIOLOGIA PLANTARUM, Issue 2 2007
Angelika Stass
The interaction of boron (B) and aluminium (Al) was investigated in 5-day-old seedlings of soybean cv. Maple Arrow. Al treatment inhibited root elongation and callose formation in root tips particularly after 4-h Al treatment. After 10 and 24 h, both parameters indicated increasing recovery from Al stress. B deficiency aggravated Al toxicity compared with B sufficiency. B deficiency did lead to an increase in unmethylated pectin in the first 3 mm of the root tip. This increase in potential binding sites is reflected in generally higher Al contents in root tips of B-deficient plants. A fractionated extraction of Al from the root tips showed that citrate-exchangeable and non-exchangeable Al steeply increased up to 4 h, but then decreased after 10- and 24-h Al treatment faster in B-sufficient than in B-deficient plants. This decrease of Al contents can be explained by an Al-enhanced release of citrate from the root tips after 10-h Al treatment. However, the citrate exudation rate was the same (after 10 h) or even lower (after 24 h) in B-sufficient plants and thus cannot explain the faster decrease in Al contents of the root tips compared with the B-deficient plants. We, therefore, propose that under B deficiency, Al is more strongly bound by the pectic network of the cell wall of the root tips, which delays or prevents the recovery from initial Al stress through exudation of citrate, and thus explains the greater Al sensitivity of B-deficient common bean roots. [source]

A physiological overview of the genetics of flowering time control

PLANT BIOTECHNOLOGY JOURNAL, Issue 1 2005
Georges Bernier
Summary Physiological studies on flowering time control have shown that plants integrate several environmental signals. Predictable factors, such as day length and vernalization, are regarded as ,primary', but clearly interfere with, or can even be substituted by, less predictable factors. All plant parts participate in the sensing of these interacting factors. In the case of floral induction by photoperiod, long-distance signalling is known to occur between the leaves and the shoot apical meristem (SAM) via the phloem. In the long-day plant, Sinapis alba, this long-distance signalling has also been shown to involve the root system and to include sucrose, nitrate, glutamine and cytokinins, but not gibberellins. In Arabidopsis thaliana, a number of genetic pathways controlling flowering time have been identified. Models now extend beyond ,primary' controlling factors and show an ever-increasing number of cross-talks between pathways triggered or influenced by various environmental factors and hormones (mainly gibberellins). Most of the genes involved are preferentially expressed in meristems (the SAM and the root tip), but, surprisingly, only a few are expressed preferentially or exclusively in leaves. However, long-distance signalling from leaves to SAM has been shown to occur in Arabidopsis during the induction of flowering by long days. In this review, we propose a model integrating physiological data and genes activated by the photoperiodic pathway controlling flowering time in early-flowering accessions of Arabidopsis. This model involves metabolites, hormones and gene products interacting as long- or short-distance signalling molecules. [source]

A comparison of ammonium, nitrate and proton net fluxes along seedling roots of Douglas-fir and lodgepole pine grown and measured with different inorganic nitrogen sources

PLANT CELL & ENVIRONMENT, Issue 3 2008
B. J. HAWKINS
ABSTRACT Significant spatial variability in NH4+, NO3, and H+ net fluxes was measured in roots of young seedlings of Douglas-fir (Pseudotsuga menziesii) and lodgepole pine (Pinus contorta) with ion-selective microelectrodes. Seedlings were grown with NH4+, NO3,, NH4NO3 or no nitrogen (N), and were measured in solutions containing one or both N ions, or no N in a full factorial design. Net NO3, and NH4+ uptake and H+ efflux were greater in Douglas-fir than lodgepole pine and in roots not exposed to N in pretreatment. In general, the rates of net NH4+ uptake were the same in the presence or absence of NO3,, and vice versa. The highest NO3, influx occurred 0,30 mm from the root apex in Douglas-fir and 0,10 mm from the apex in lodgepole pine. Net NH4+ flux was zero or negative (efflux) at Douglas-fir root tips, and the highest NH4+ influx occurred 5,20 mm from the root tip. Lodgepole pine had some NH4+ influx at the root tips, and the maximum net uptake 5 mm from the root tip. Net H+ efflux was greatest in the first 10 mm of roots of both species. This study demonstrates that nutrient uptake by conifer roots can vary significantly across different regions of the root, and indicates that ion flux profiles along the roots may be influenced by rates of root growth and maturation. [source]

The mechanism of boron tolerance for maintenance of root growth in barley (Hordeum vulgare L.)

PLANT CELL & ENVIRONMENT, Issue 8 2007
EUN-YOUNG CHOI
ABSTRACT Cultivar differences in root elongation under B toxic conditions were observed in barley (Hordeum vulgare L.). A significant increase in the length and width of the root meristematic zone (RMZ) was observed in Sahara 3771 (B tolerant) when it was grown under excessive B concentration, compared to when grown at adequate B supply. This coincided with an increase in cell width and cell numbers in the meristematic zone (MZ), whereas a significant decrease in the length and no significant effect on the width of the MZ was observed in Clipper (B intolerant) when it was grown under excessive B supply. This was accompanied by a decrease in cell numbers, but an increase in the length and width of individual cells present along the MZ. Excessive B concentrations led to a significantly lower osmotic potential within the cell sap of the root tip in SloopVic (B tolerant) and Sahara 3771, while the opposite was observed in Clipper. Enhanced sugar levels in the root tips of SloopVic were observed between 48 and 96 h after excess B was applied. This coincided with an increase in the root elongation rate and with a 2.7-fold increase in sucrose level within mature leaf tissue. A significant decrease in reducing sugar levels was observed in the root tips of Clipper under excessive B concentrations. This coincided with significantly lower root elongation rates and lower sucrose levels in leaf tissues. Results indicate a B tolerance mechanism associated with a complex control of sucrose levels between leaf and root tip that assist in maintaining root growth under B toxicity. [source]

Root structure and cellular chloride, sodium and potassium distribution in salinized grapevines

PLANT CELL & ENVIRONMENT, Issue 6 2003
R. STOREY
ABSTRACT X-ray microanalysis was used to study the patterns of K+, Na+ and Cl, accumulation in salinized (25 mm NaCl) and non-salinized grapevine (Vitis) roots. The aim was to determine whether NaCl affects patterns of Cl, accumulation differentially in the roots of a Cl, -excluding genotype and a non-excluding genotype. Two regions of fibrous roots were analysed: (1) a region 2,3 mm basipetal to the root tip; and (2) a region of the root 10,12 mm basipetal to the root tip where the outermost layer is the hypodermis. The ion contents of the hypodermis, cortex, endodermis and pericycle vacuoles were analysed. Data were also collected from the cytoplasm of the endodermal and pericycle cells. The analyses showed that the ion profiles of the hypodermis and the endodermis were significantly different from those of the cortex and pericycle. The hypodermis and endodermis had higher K+ and lower Na+ and Cl, than surrounding cells. Some changes due to salinity such as increased K+ concentrations in the hypodermis were also noted. Chloride concentrations did not differ between the genotypes in the hypodermis, across the cortex or in the endodermis, but were higher in the pericycle of the excluder in comparison with the non-excluding genotype. However, K+/Na+ ratios of the cortex and endodermis were higher in the excluder. The pericycle cells exhibited the greatest ability to sequester Na+ and Cl, in vacuoles. Overall the data show cell-type-specific ion accumulation patterns and small but significant differences were found between genotypes. The possibility that these accumulation patterns arise from differences in uptake properties of cell types and/or result from the spatial distribution of the cell types along the competing symplastic and apoplastic ion transport pathways across the root is discussed. [source]

Long-distance transport of gases in plants: a perspective on internal aeration and radial oxygen loss from roots

PLANT CELL & ENVIRONMENT, Issue 1 2003
T. D. COLMER
ABSTRACT Internal transport of gases is crucial for vascular plants inhabiting aquatic, wetland or flood-prone environments. Diffusivity of gases in water is approximately 10 000 times slower than in air; thus direct exchange of gases between submerged tissues and the environment is strongly impeded. Aerenchyma provides a low-resistance internal pathway for gas transport between shoot and root extremities. By this pathway, O2 is supplied to the roots and rhizosphere, while CO2, ethylene, and methane move from the soil to the shoots and atmosphere. Diffusion is the mechanism by which gases move within roots of all plant species, but significant pressurized through-flow occurs in stems and rhizomes of several emergent and floating-leaved wetland plants. Through-flows can raise O2 concentrations in the rhizomes close to ambient levels. In general, rates of flow are determined by plant characteristics such as capacity to generate positive pressures in shoot tissues, and resistance to flow in the aerenchyma, as well as environmental conditions affecting leaf-to-air gradients in humidity and temperature. O2 diffusion in roots is influenced by anatomical, morphological and physiological characteristics, and environmental conditions. Roots of many (but not all) wetland species contain large volumes of aerenchyma (e.g. root porosity can reach 55%), while a barrier impermeable to radial O2 loss (ROL) often occurs in basal zones. These traits act synergistically to enhance the amount of O2 diffusing to the root apex and enable the development of an aerobic rhizosphere around the root tip, which enhances root penetration into anaerobic substrates. The barrier to ROL in roots of some species is induced by growth in stagnant conditions, whereas it is constitutive in others. An inducible change in the resistance to O2 across the hypodermis/exodermis is hypothesized to be of adaptive significance to plants inhabiting transiently waterlogged soils. Knowledge on the anatomical basis of the barrier to ROL in various species is scant. Nevertheless, it has been suggested that the barrier may also impede influx of: (i) soil-derived gases, such as CO2, methane, and ethylene; (ii) potentially toxic substances (e.g. reduced metal ions) often present in waterlogged soils; and (iii) nutrients and water. Lateral roots, that remain permeable to O2, may be the main surface for exchange of substances between the roots and rhizosphere in wetland species. Further work is required to determine whether diversity in structure and function in roots of wetland species can be related to various niche habitats. [source]

Spatial separation of light perception and growth response in maize root phototropism

PLANT CELL & ENVIRONMENT, Issue 9 2002
J. L. Mullen
Abstract Although the effects of gravity on root growth are well known and interactions between light and gravity have been reported, details of root phototropic responses are less documented. We used high-resolution image analysis to study phototropism in primary roots of Zea mays L. Similar to the location of perception in gravitropism, the perception of light was localized in the root cap. Phototropic curvature away from the light, on the other hand, developed in the central elongation zone, more basal than the site of initiation of gravitropic curvature. The phototropic curvature saturated at approximately 10 µmol m,2 s,1 blue light with a peak curvature of 29 ± 4°, in part due to induction of positive gravitropism following displacement of the root tip from vertical during negative phototropism. However, at higher fluence rates, development of phototropic curvature is arrested even if gravitropism is avoided by maintaining the root cap vertically using a rotating feedback system. Thus continuous illumination can cause adaptation in the signalling pathway of the phototropic response in roots. [source]

Aluminum induces chromosome aberrations, micronuclei, and cell cycle dysfunction in root cells of Vicia faba

ENVIRONMENTAL TOXICOLOGY, Issue 2 2010
Min Yi
Abstract Aluminum (Al) exists naturally in air, water, and soil, and also in our diet. Al can be absorbed into the human body and accumulates in different tissues, which has been linked to the occurrence of Alzheimer's disease and various neurological disorders. By using Vicia cytogenetic tests, which are commonly used to monitor the genotoxicity of environmental pollutants, cytogenetic effects of aluminum (AlCl3) were investigated in this study. Present results showed that Al caused significant increases in the frequencies of micronuclei (MN) and anaphase chromosome aberrations in Vicia faba root tips exposed to Al over a concentration-tested range of 0.01,10 mM for 12 h. The frequency of micronucleated cells was higher in Al-treated groups at pH 4.5 than that at pH 5.8. Similarly, AlCl3 treatment caused a decrease in the number of mitotic cells in a dose- and pH-dependent manner. The number of cells in each mitotic phase changed in Al-treated samples. Mitotic indices (MI) decreased with the increases of pycnotic cells. Our results demonstrate that aluminum chloride is a clear clastogenic/genotoxic and cytotoxic agent in Vicia root cells. The V. faba cytogenetic test could be used for the genotoxicity monitoring of aluminum water contamination. © 2009 Wiley Periodicals, Inc. Environ Toxicol, 2010. [source]

Phylogenetic diversity of non-nodulating Rhizobium associated with pine ectomycorrhizae

FEMS MICROBIOLOGY ECOLOGY, Issue 3 2009
Megumi Tanaka
Abstract Most Rhizobium species described are symbionts that form nodules on legume roots; however, non-nodulating strains of Rhizobium are also widespread in nature. Unfortunately, knowledge of non-nodulating Rhizobium is quite limited compared with nodulating Rhizobium. Here, we studied the phylogenetic diversity of Rhizobium species that inhabit Japanese red pine roots (Pinus densiflora). Because fine roots of pine trees are usually colonized by ectomycorrhizal fungi in nature, we mainly used ectomycorrhizal root tips for bacterial isolation. Out of 1195 bacteria isolated from 75 independent root samples from the field and greenhouse experiments, 102 isolates were confirmed to be Rhizobium following partial 16S rRNA gene analysis. Rhizobium species were occasionally dominant in culturable bacterial communities, whereas no Rhizobium species were isolated from the soil itself. Molecular phylogenetic analyses using 16S rRNA, atpD, and recA gene sequences revealed that isolated Rhizobium strains were phylogenetically diverse and that several were distantly related to known Rhizobium species. Considering that a single species of pine is associated with unique and phylogenetically diverse Rhizobium populations, we should pay more attention to non-nodulating strains to better understand the diversity, ecology, and evolution of the genus Rhizobium and plant,Rhizobium associations. [source]

Biomass, nutrient and pigment content of beech (Fagus sylvatica) saplings infected with Phytophthora citricola, P. cambivora, P. pseudosyringae and P. undulata

FOREST PATHOLOGY, Issue 2 2004
F. Fleischmann
Summary Fagus sylvatica saplings were infected with Phytophthora citricola, Phytophthora cambivora, Phytophthora pseudosyringae and Phytophthora undulata to study the influence of these root pathogens on total belowground and aboveground biomass, on the nutrient distribution within plants, on the concentration of plastid pigments, including tocopherol and on components of the xanthophyll cycle. Phytophthora citricola and P. cambivora infection significantly reduced total biomass of beech when compared with control plants and finally most of these plants died at the end of the experiment. However, beech invaded by the other two Phytophthora spp. did not differ from control plants and none of them was killed. Fine root length as well as the number of root tips of all infected beeches were reduced between 30 and 50%. The excellent growth of beech infected with P. pseudosyringae and P. undulata when compared with control plants was correlated with a strong increase of important root efficiency parameters. Phytophthora citricola and P. cambivora caused a significant reduction in nitrogen concentration of leaves in comparison with control and other infected plants, whereas this nutrient was slightly increased in fine and coarse roots. Furthermore, the phosphorus and potassium concentrations in leaves were impaired after infection with P. citricola. However, foliar concentrations of Ca and Mg were not affected by the different Phytophthora spp., whereas fine and coarse roots were significantly enriched with Ca in beech infected with P. citricola or P. cambivora. The concentrations of , -tocopherol and xanthophyll cycle pigments were increased in plants infected by P. citricola and P. cambivora, indicating that several reactive oxygen species might be formed in leaves during infection. Résumé Des plants de Fagus sylvatica ont été infectés par Phytophthora citricola, Phytophthora cambivora, Phytophthora pseudosyringae et Phytophthora undulata pour étudier l'effet de ces pathogènes racinaires sur la biomasse totale aérienne et racinaire, la distribution des éléments minéraux dans les plantes et la concentration en pigments des plastes, tocophérol et composants du cycle des xanthophylles. L'infection par P. citricola et P. cambivora a entraîné une réduction significative de la biomasse totale par rapport aux plantes témoins et la plupart des plants infectés sont morts au cours de l'expérience. Par contre, les hêtres infectés par les deux autres espèces de Phytophthora ne différent pas des témoins et aucune mortalité n'a été observée. Chez tous les hêtres infectés, une réduction de 30 à 50% de la longueur de racines fines et du nombre d'extrémités racinaires a été observée. La très bonne croissance des plants infectés par P. pseudosyringae et P. undulata par rapport aux témoins est associée à une forte augmentation de paramètres importants d'efficience racinaire. P. citricola et P. cambivora ont causé une réduction significative de la concentration foliaire en azote par rapport aux plantes témoins et aux autres plantes infectées, alors que la concentration était légèrement augmentée dans les fines et grosses racines. De plus, la concentration foliaire en phosphore et potassium a été altérée après infection par P. citricola. Les concentrations foliaires en Ca et Mg n'ont pas été affectées par les différentes espèces de Phytophthora, les fines et grosses racines étant significativement enrichies en Ca chez les plants infectés par P. citricola ou P. cambivora. La concentration en , -tocophérol et pigments du cycle des xanthophylles a augmenté dans les plants infectés par P. citricola et P. cambivora, suggérant la formation de plusieurs espèces actives de l'oxygène dans les feuilles pendant l'infection. Zusammenfassung Buchensämlinge wurden mit Phytophthora citricola, Phytophthora cambivora, Phytophthora pseudosyringae und mit Phytophthora undulata infiziert, um den Einfluss dieser Wurzelpathogene auf die oberirdische und unterirdische Biomasse, auf die Nährstoffverteilung innerhalb verschiedener Pflanzenorgane, sowie auf die Gehalte unterschiedlicher Photosynthesepigmente und Komponenten des Xanthophyll- Zyklus studieren zu können. Die Infektion mit P. citricola und P. cambivora führte zu einer deutlich reduzierten Gesamtbiomasse und am Versuchsende waren die meisten Pflanzen abgestorben. Dagegen überlebten alle mit P. pseudosyringae oder P. undulata infizierten Buchen und sie zeigten keine Unterschiede in ihren Biomassen verglichen mit Kontrollpflanzen bzw. übertrafen diese sogar. Die Feinwurzellänge und die Anzahl ihrer Wurzelspitzen war bei allen Phytophthora infizierten Pflanzen zwischen 30 und 50% im Vergleich zu denen der Kontrollen reduziert. Das ausgezeichnete Wachstum der P. pseudosyringae und P. undulata infizierten Pflanzen ging mit stark gesteigerten Wurzeleffizienzparametern einher. Die P. citricola und P. cambivora Infektion führte zu reduzierten Stickstoffgehalten in den Blättern. Die Gehalte in den Wurzeln waren jedoch leicht erhöht. Zudem wurden reduzierte Gehalte an Phosphor und Kalium in den Blättern gemessen. Die Calcium und Magnesium- Konzentrationen der Blätter unterschieden sich nicht von denen der Kontrollen. Allerdings wurde eine Calcium-Anreicherung in den Fein- und Grobwurzeln infizierter Pflanzen gemessen. Weiterhin zeigten wir, dass die Konzentrationen von , -Tocopherol und Pigmenten des Xanthophyll-Zyklus in Blättern P. citricola und P. cambivora infizierter Pflanzen erhöht waren, was möglicherweise auf die Bildung reaktiver Sauerstoffspezies hindeutet. [source]

Residual bacteria in root apices removed by a diagonal root-end resection: a histopathological evaluation

INTERNATIONAL ENDODONTIC JOURNAL, Issue 6 2008
S. Lin
Abstract Aim, To assess bacteria in the apical portion of the root end after 45° root-end resection in teeth with persistent periapical lesions. Methodology, The study included 27 apical root segments from patients with persistent periapical lesions. Histological sections of the coronal part of the amputated root segment were stained with Brown and Brenn to detect the presence of bacteria in the main root canal and/or in irregular root spaces and dentinal tubules. The quality of each root canal filling was evaluated using preoperative radiographs of filling, length of root filling as assessed from the distance between its apical end and the radiographic apex, diameter of apical preparation, and presence of apical perforations or deviations from the root canal. Two endodontists, blinded to the bacteriological results, independently evaluated the radiographs. Results, Bacteria were present in 23 (85.2%) specimens: five in only the main canal (21.7%), 10 in only the dentinal tubules and irregular spaces (43.5%), and eight in both irregular spaces and dentinal tubules and in the main root canal (34.8%). No correlation was found between the technical quality of the root filling assessed radiographically and bacterial presence in the central canal or irregular areas. Conclusions, Infected irregular areas were found in the root tips of teeth with persistent periapical lesions. This was found regardless of the radiographic quality of the root filling. Diagonal, 45° root-end resection may expose such contaminated irregularities to the periapical tissue. [source]

What youngsters say about adults: seedling roots reflect clonal traits of adult plants

JOURNAL OF ECOLOGY, Issue 3 2007
MARIE, MILAUEROVÁ
Summary 1Grime's theory on plant strategies predicts that the set of traits present in established plants is not correlated with that found in the regenerative stage of the life cycle. We tested this prediction and further investigated whether clonal growth traits, which are found in adult plants but also affect regeneration, are correlated with seedling traits. 2We characterized seedling root systems by their total length, number of root tips and several architectural parameters (length of exterior and interior root links and two topological indices). These below-ground traits were supplemented by the ratio of leaf area to root length, representing relative investment into photosynthesizing surface. We compared seedling traits with clonal growth traits, adult plant heights, and species positions on gradients of nitrogen and water availability. 3Plant species with limited horizontal spread by clonal growth exhibited a larger relative investment in photosynthetic area and also developed larger root systems as seedlings. 4Seedlings of species with taller shoots and those which occur naturally at nutrient-rich sites developed both larger roots and more dichotomously branched root systems (with higher total length and more branches). 5Taking phylogenetic inertia into account showed that this explained large parts of the variation in seedling traits. Relationships between clonal spread and seedling traits were strengthened by phylogenetic correction. 6Our study shows that some of the traits of clonal growth affect both the established and the regenerative stages of the life cycle, suggesting that an evolutionary trade-off exists between the ability to spread clonally and performance at the seedling stage. Species not able to escape from less favourable conditions by extensive clonal spread seem to be more able to exploit the location in which they germinate. [source]

The significance of organic-anion exudation for the aluminum resistance of primary triticale derived from wheat and rye parents differing in aluminum resistance

JOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 4 2008
Angelika Stass
Abstract Eight primary octoploid triticale genotypes (xTriticosecale Wittmack) derived from four wheat cultivars (Triticum aestivum L.) and two rye inbred lines (Secale cereale L.) differing in aluminum (Al) resistance were investigated with respect to their response to Al supply. Aluminum-induced inhibition of root elongation (48 h, 25 µM Al supply), callose formation, and the accumulation of Al in root tips (4 h, 25 µM Al supply) were used as parameters to assess Al resistance. Using these parameters, the existing information on Al resistance of the wheat and rye cultivars was generally confirmed. The triticale cultivars showed a wide range of Al resistance amongst the Al-sensitive wheat and the Al-resistant rye cultivars. The rye parents and the Al-resistant wheat parent Carazinho were characterized by Al-induced exudation particularly of citrate but also of malate from whole root systems of 14 d old seedlings (8 h, 50 µM Al supply). Regression analysis revealed that the degree of Al resistance of the triticale genotypes was closely related to the Al-induced citrate exudation, which was mainly controlled by the Al resistance of the wheat parent. [source]

Growth and nutrient uptake of tea under different aluminium concentrations

JOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 9 2008
Ka Fai Fung
Abstract BACKGROUND: The uptake of essential nutrients such as P, Fe, K, Ca and Mg is depressed by Al in most plants. This study aimed to investigate the concentrations at which Al could be toxic to C. sinensis. The suppression of nutrient uptake was investigated by comparing growth and nutrient uptake at different Al doses. The quantification of Al in apoplasm, symplasm and cell wall of C. sinensis was also studied. RESULTS: In the absence of Al, the growth of C. sinensis was retarded. Test doses over 1 mM Al were toxic to C. sinensis. At concentrations of 0.25 or 0.5 mM, distinct rhizostimulation was noted, and within a short period (2 weeks), the biomass of these seedlings increased by 44 and 35%, respectively, compared to 0 and 14% in control and 1 mM Al, respectively. In general, at beneficial doses (0.25, 0.5), Al stimulated the uptake of Ca, Mg, K and Mn, whereas the uptake of Fe, Cu and Zn was retarded. Fine roots of the seedlings had the highest levels of Al, compared to leaves, branches and main roots. In the root tips, most of the Al was present in the soluble fractions of the apoplasm and symplasm, and very low levels of Al was bound to the cell walls, which was in good agreement with the observed mobility of Al in C. sinensis. CONCLUSION: The results of the present study support the view that Al plays a nutritive role for C. sinensis. The rhizostimulatory effects of Al on C. sinensis have been explained as a consequence of enhanced nutrient uptake. Copyright © 2008 Society of Chemical Industry [source]

Rhizoremediation of lindane by root-colonizing Sphingomonas

MICROBIAL BIOTECHNOLOGY, Issue 1 2008
Dietmar Böltner
Summary We used a two-step enrichment approach to isolate root-colonizing hexachlorocyclohexane (HCH)-degrading microorganisms. The first step consists of the use of classical liquid enrichment to isolate ,-HCH degraders. The ,-HCH-degrading microbes were attached in mass to corn seeds sown in soil with ,-HCH, and after plant development we rescued bacteria growing on root tips. Bacteria were then subjected to a second enrichment round in which growth on liquid medium with ,-HCH and inoculation of corn seeds were repeated. We then isolated bacteria on M9 minimal medium with ,-HCH from root tips. We were able to isolate four Sphingomonas strains, all of which degraded ,-, ,-, ,- and ,-HCH. Two of the strains were particularly good colonizers of corn roots, reaching high cell density in vegetated soil and partly removing ,-HCH. In contrast, these bacteria performed poorly in unplanted soils. This study supports the hypothesis that the removal of persistent toxic chemicals can be accelerated by combinations of plants and bacteria, a process generally known as rhizoremediation. [source]

Ectomycorrhizal fungal succession in mixed temperate forests

NEW PHYTOLOGIST, Issue 2 2007
Brendan D. Twieg
Summary ,,Ectomycorrhizal (ECM) fungal communities of Douglas-fir (Pseudotsuga menziesii) and paper birch (Betula papyrifera) were studied along a chronosequence of forest development after stand-replacing disturbance. Previous studies of ECM succession did not use molecular techniques for fungal identification or lacked replication, and none examined different host species. ,,Four age classes of mixed forests were sampled: 5-, 26-, 65-, and 100-yr-old, including wildfire-origin stands from all four classes and stands of clearcut origin from the youngest two classes. Morphotyping and DNA sequences were used to identify fungi on ECM root tips. ,,ECM fungal diversities were lower in 5-yr-old than in older stands on Douglas-fir, but were similar among age classes on paper birch. Host-specific fungi dominated in 5-yr-old stands, but host generalists were dominant in the oldest two age classes. ECM fungal community compositions were similar in 65- and 100-yr-old stands but differed among all other pairs of age classes. ,,Within the age range studied, site-level ECM fungal diversity reached a plateau by the 26-yr-old age class, while community composition stabilized by the 65-yr-old class. Simple categories such as ,early stage', ,multi stage', and ,late stage' were insufficient to describe fungal species' successional patterns. Rather, ECM fungal succession may be best described in the context of stand development. [source]

Cytological and enzymatic responses to aluminium stress in root tips of Norway spruce seedlings

NEW PHYTOLOGIST, Issue 3 2004
Nina Elisabeth Nagy
Summary ,,Aluminium (Al) stress reduces plant growth. However, some species such as Norway spruce (Picea abies) seem to tolerate high Al concentrations. The aim of this study was to investigate characteristics possibly involved in Al tolerance in Norway spruce seedlings. ,,Seedlings (10-d-old) were exposed to Al3+ concentrations of 0.5 and 5 mm for up to 168 h. The effect of Al stress on root growth, cell morphology and Al distribution, callose production, and peroxidase and chitinase activity was analysed. ,,Root growth decreased after 1 d and 2 d with 5 and 0.5 mm Al, respectively. Callose concentration increased strongly after 6 h treatment with 5 mm Al. The activity of many peroxidase and chitinase isoforms decreased after 1,24 h exposure of both treatments. Several isoforms increased after 48,168 h exposure to 5 mm Al. ,,We postulate that, with external Al concentrations 0.5 mm or lower, an increased production above constitutive levels of peroxidase or chitinase is not required for Al tolerance in young Norway spruce seedlings. High constitutive levels of peroxidase and chitinase in this species may be part of this Al tolerance. [source]

Characterization of the Arabidopsis metallothionein gene family: tissue-specific expression and induction during senescence and in response to copper

NEW PHYTOLOGIST, Issue 2 2003
Woei-Jiun Guo
Summary ,Expression and regulation of Arabidopsis metallothionein (MT) genes were investigated to examine the functions of MTs in plants. ,To examine the tissue-specific expression of MT genes, GUS reporter gene activity driven by promoters of MT1a, MT2a, MT2b and MT3 was analysed in transgenic plants. ,MT1a and MT2b are expressed in the phloem of all organs and are copper (Cu)-inducible; MT2a and MT3, by contrast, are expressed predominantly in mesophyll cells and are also induced by Cu in young leaves and at root tips. Expression of MT genes is highly induced by Cu in trichomes and increases during senescence. Expression of MT4 genes is restricted to seeds. ,We propose that plant MTs have distinct functions in heavy metal homeostasis, especially for Cu: MT1a and MT2b are involved in the distribution of Cu via the phloem, while MT2a and MT3 chaperone excess metals in mesophyll cells and root tips. These functional capabilities may allow MTs to play a role in mobilization of metal ions from senescing leaves and the sequestration of excess metal ions in trichomes. [source]

Developmental shifts in watermelon growth and reproduction caused by the squash bug, Anasa tristis

NEW PHYTOLOGIST, Issue 2 2002
Maciej Biernacki
Summary ,,Compared with leaf-feeding herbivores, little is known about how sap-feeding herbivores affect plant growth, morphology and reproduction. This study examines effects of the sap-feeding squash bug ( Anasa tristis ) on watermelon ( Citrullus lanatus ) root, leaf and reproductive structures. ,,Plants at the four-leaf stage were exposed to different densities of caged squash bugs for 67 d (to plant maturity). ,,Initial effects were on roots. Herbivory was associated with a significant reduction in mean total root length, root surface area and number of root tips, as well as an increase in root diameters. Herbivore-exposed plants had significantly more leaves, although leaf lifespan was decreased. Both total plant dry mass and fruit dry mass per unit leaf area were significantly greater in controls. Significant effects of herbivores on plant reproductive traits included delayed flower formation (by 7,12 d), change in floral sex ratio (in favor of femaleness), increased fruit abortion, and smaller fruit size. ,,Developmental consequences were related to changes in plant water relations, including decreased water-use efficiency. Water use in treated plants was three to nine times greater per unit of plant dry mass than in controls. [source]

Effect of boron on the expression of aluminium toxicity in Phaseolus vulgaris

CASIROZ: Root Parameters and Types of Ectomycorrhiza of Young Beech Plants Exposed to Different Ozone and Light Regimes

PLANT BIOLOGY, Issue 2 2007
eleznik
Abstract: Tropospheric ozone (O3) triggers physiological changes in leaves that affect carbon source strength leading to decreased carbon allocation below-ground, thus affecting roots and root symbionts. The effects of O3 depend on the maturity-related physiological state of the plant, therefore adult and young forest trees might react differently. To test the applicability of young beech plants for studying the effects of O3 on forest trees and forest stands, beech seedlings were planted in containers and exposed for two years in the Kranzberg forest FACOS experiment (Free-Air Canopy O3 Exposure System, http:www.casiroz.de) to enhanced ozone concentration regime (ambient [control] and double ambient concentration, not exceeding 150 ppb) under different light conditions (sun and shade). After two growing seasons the biomass of the above- and below-ground parts, beech roots (using WinRhizo programme), anatomical and molecular (ITS-RFLP and sequencing) identification of ectomycorrhizal types and nutrient concentrations were assessed. The mycorrhization of beech seedlings was very low (ca. 5 % in shade, 10 % in sun-grown plants), no trends were observed in mycorrhization (%) due to ozone treatment. The number of Cenococcum geophilum type of ectomycorrhiza, as an indicator of stress in the forest stands, was not significantly different under different ozone treatments. It was predominantly occurring in sun-exposed plants, while its majority share was replaced by Genea hispidula in shade-grown plants. Different light regimes significantly influenced all parameters except shoot/root ratio and number of ectomycorrhizal types. In the ozone fumigated plants the number of types, number of root tips per length of 1 to 2 mm root diameter, root length density per volume of soil and concentration of Mg were significantly lower than in control plants. Trends to a decrease were found in root, shoot, leaf, and total dry weights, total number of root tips, number of vital mycorrhizal root tips, fine root (mass) density, root tip density per surface, root area index, concentration of Zn, and Ca/Al ratio. Due to the general reduction in root growth indices and nutrient cycling in ozone-fumigated plants, alterations in soil carbon pools could be predicted. [source]

A comparison of ammonium, nitrate and proton net fluxes along seedling roots of Douglas-fir and lodgepole pine grown and measured with different inorganic nitrogen sources