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Root Exudates (root + exudate)

Distribution by Scientific Domains

Life Sciences	62%
Earth and Environmental Science	21%
Chemistry	15%

Distribution within Life Sciences

Plant Science	54%
Microbial Ecology	19%

Selected Abstracts

Bioassay and Identification of Root Exudates of Three Fruit Tree Species

JOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 3 2007
Jiang-Hong Zhang
Abstract A laboratory bioassay was designed to determine the allelopathic potential of root exudates of three fruit tree species on apple germination. The results showed that root exudates of apple (Malus pumila L.) and peach (Prunus persica L.), each at concentrations of 0.02 and 0.2 mg/L, inhibited germination and radicle growth of apple seeds by 56.7%, 60.7%, 51.5%, and 59.3%, respectively. The corresponding shoot growth inhibition rate was 49.5%, 46.7%, 36.4%, and 44%, respectively. Root exudates of jujube (Ziziphus jujuba Mill.) had no significant effect on apple seeds. Qualitative determination of root exudates of apple, peach, and jujube tree was developed with gas chromatography-mass spectrometry. The root exudates of apple seedlings mainly contain organic acids, glycol, esters, and benzenphenol derivatives. Peach root exudates contained phenolic acids and benzenphenol derivatives in addition to two unidentified compounds. The root exudates of jujube did not contain any phenolic acids. [source]

Increase in the fracture toughness and bond energy of clay by a root exudate

EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 5 2008
B. Zhang
Summary Root exudates help drive the formation of the rhizosphere by binding soil particles, but the underlying physical mechanisms have not been quantified. This was addressed by measuring the impact of a major component of root exudates, polygalacturonic acid (PGA), on the interparticle bond energy and fracture toughness of clay. Pure kaolinite was mixed with 0, 1.2, 2.4, 4.9 or 12.2 g PGA kg,1 to form test specimens. Half of the specimens were washed repeatedly to remove unbound PGA and evaluate the persistence of the effects, similar to weathering in natural soils. Fracture toughness, KIC, increased exponentially with added PGA, with washing increasing this trend. In unwashed specimens KIC ranged from 54.3 ± 2.5 kPa m,1/2 for 0 g PGA kg,1 to 86.9 ± 4.7 kPa m,1/2 for 12.2 g PGA kg,1. Washing increased KIC to 61.3 ± 1.2 kPa m,1/2 for 0 g PGA kg,1 and 132.1 ± 4.9 kPa m,1/2 for 12.2 g PGA kg,1. The apparent bond energy, ,, of the fracture surface increased from 5.9 ± 0.6 J m,2 for 0 g kg,1 to 12.0 ± 1.1 J m,2 for 12.2 g kg,1 PGA in the unwashed specimens. The washed specimens had , of 13.0 ± 1.9 J m,2 for 0 g kg,1 and 21.3 ± 2.6 J m,2 for 12.2 g PGA kg,1. Thus PGA, a major component of root exudates, has a large impact on the fracture toughness and bond energy of clay, and is likely to be a major determinant in the formation of the rhizosphere. This quantification of the thermodynamics of fracture will be useful for modelling rhizosphere formation and stability. [source]

Establishment of Azotobacter on plant roots: chemotactic response, development and analysis of root exudates of cotton (Gossypium hirsutum L.) and wheat (Triticum aestivum L.)

JOURNAL OF BASIC MICROBIOLOGY, Issue 5 2007
Rakesh Kumar
Abstract Biofertilizers contribute in N2 fixation, P solubilization, phytohormone production and thus enhance plant growth. Beneficial plant-microbe interactions and the stability and effectiveness of biofertilizer depend upon the establishment of bacterial strains in the rhizosphere of the plant. This interaction depends upon many factors, one of them being plant exudates. Root exudates are composed of small organic molecules like carbonic acids, amino acids or sugars etc., which are released into the soil and bacteria can be attracted towards these exudates due to chemotaxis. The chemotactic behaviour of Azotobacter strains was studied using cotton (Desi HD 123 and American H 1098) and wheat (WH 711) seedlings and the root exudates of these two plants were chemically characterized. Analysis of the root exudates revealed the presence of sugars and simple polysaccharides (glucose), amino acids (glutamate, lysine) and organic acids (citric acid, succinic acid, maleic acid, malonic acid). Differences between cotton cultivars in root exudates were observed which influenced chemotactic response in Azotobacter. These results indicate colonization with rhizobacteria which implies that optimal symbionts, on the sides of both plant cultivar and bioinoculant bacteria can lead to better plant growth under cultivation conditions. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Bioassay and Identification of Root Exudates of Three Fruit Tree Species

Root exudates of the hyperaccumulator Thlaspi caerulescens do not enhance metal mobilization

NEW PHYTOLOGIST, Issue 3 2001
F. J. Zhao
Summary ,,To examine whether root exudates of the Zn/Cd hyperaccumulator Thlaspi caerulescens play a role in metal hyperaccumulation, we compared the metal mobilization capacity of root exudates collected from two ecotypes of T. caerulescens, and from the nonaccumulators wheat (Triticum aestivum) and canola (Brassica napus). ,,Plants were grown hydroponically and three treatments (control, ,Fe and ,Zn) were later imposed for 2 wk before collection of root exudates. ,,On a basis of root d. wt, the total soluble organic C in the root exudates of T. caerulescens was similar to that of wheat, and significantly higher than that of canola. In all treatment, the root exudates of T. caerulescens and canola mobilized little Cu and Zn from Cu- or Zn-loaded resins, and little Zn, Cd, Cu or Fe from a contaminated calcareous soil. By contrast, the root exudates of wheat generally mobilized more metals from both resin and soil. In particular, the ,Fe treatment, and to a lesser extent the ,Zn treatment, elicited large increases in the metal mobilization capacity of the root exudates from wheat. ,,We conclude that root exudates from T. caerulescens do not significantly enhance mobilization of Zn and Cd, and therefore are not involved in Zn and Cd hyperaccumulation. [source]

Increase in the fracture toughness and bond energy of clay by a root exudate

Modelling increased soil cohesion due to roots with EUROSEM

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 13 2008
S. De Baets
Abstract As organic root exudates cause soil particles to adhere firmly to root surfaces, roots significantly increase soil strength and therefore also increase the resistance of the topsoil to erosion by concentrated flow. This paper aims at contributing to a better prediction of the root effects on soil erosion rates in the EUROSEM model, as the input values accounting for roots, presented in the user manual, do not account for differences in root density or root architecture. Recent research indicates that small changes in root density or differences in root architecture considerably influence soil erosion rates during concentrated flow. The approach for incorporating the root effects into this model is based on a comparison of measured soil detachment rates for bare and for root-permeated topsoil samples with predicted erosion rates under the same flow conditions using the erosion equation of EUROSEM. Through backwards calculation, transport capacity efficiencies and corresponding soil cohesion values can be assessed for bare and root-permeated topsoils respectively. The results are promising and present soil cohesion values that are in accordance with reported values in the literature for the same soil type (silt loam). The results show that grass roots provide a larger increase in soil cohesion as compared with tap-rooted species and that the increase in soil cohesion is not significantly different under wet and dry soil conditions, either for fibrous root systems or for tap root systems. Power and exponential relationships are established between measured root density values and the corresponding calculated soil cohesion values, reflecting the effects of roots on the resistance of the topsoil to concentrated flow incision. These relationships enable one to incorporate the root effect into the soil erosion model EUROSEM, through adapting the soil cohesion input value. A scenario analysis shows that the contribution of roots to soil cohesion is very important for preventing soil loss and reducing runoff volume. The increase in soil shear strength due to the binding effect of roots on soil particles is two orders of magnitude lower as compared with soil reinforcement achieved when roots mobilize their tensile strength during soil shearing and root breakage. Copyright © 2008 John Wiley & Sons, Ltd. [source]

The exopolysaccharide of Rhizobium sp.

ENVIRONMENTAL MICROBIOLOGY, Issue 8 2008
Brassica napus roots but contributes to root colonization, YAS34 is not necessary for biofilm formation on Arabidopsis thaliana
Summary Microbial exopolysaccharides (EPSs) play key roles in plant,microbe interactions, such as biofilm formation on plant roots and legume nodulation by rhizobia. Here, we focused on the function of an EPS produced by Rhizobium sp. YAS34 in the colonization and biofilm formation on non-legume plant roots (Arabidopsis thaliana and Brassica napus). Using random transposon mutagenesis, we isolated an EPS-deficient mutant of strain YAS34 impaired in a glycosyltransferase gene (gta). Wild type and mutant strains were tagged with a plasmid-born GFP and, for the first time, the EPS produced by the wild-type strain was seen in the rhizosphere using selective carbohydrate probing with a fluorescent lectin and confocal laser-scanning microscopy. We show for the fist time that Rhizobium forms biofilms on roots of non-legumes, independently of the EPS synthesis. When produced by strain YAS34 wild type, EPS is targeted at specific parts of the plant root system. Nutrient fluctuations, root exudates and bacterial growth phase can account for such a production pattern. The EPS synthesis in Rhizobium sp. YAS34 is not essential for biofilm formation on roots, but is critical to colonization of the basal part of the root system and increasing the stability of root-adhering soil. Thus, in Rhizobium sp. YAS34 and non-legume interactions, microbial EPS is implicated in root,soil interface, root colonization, but not in biofilm formation. [source]

Flux and turnover of fixed carbon in soil microbial biomass of limed and unlimed plots of an upland grassland ecosystem

ENVIRONMENTAL MICROBIOLOGY, Issue 4 2005
J. Ignacio Rangel-Castro
Summary The influence of liming on rhizosphere microbial biomass C and incorporation of root exudates was studied in the field by in situ pulse labelling of temperate grassland vegetation with 13CO2 for a 3-day period. In plots that had been limed (CaCO3 amended) annually for 3 years, incorporation into shoots and roots was, respectively, greater and lower than in unlimed plots. Analysis of chloroform-labile C demonstrated lower levels of 13C incorporation into microbial biomass in limed soils compared to unlimed soils. The turnover of the recently assimilated 13C compounds was faster in microbial biomass from limed than that from unlimed soils, suggesting that liming increases incorporation by microbial communities of root exudates. An exponential decay model of 13C in total microbial biomass in limed soils indicated that the half-life of the tracer within this carbon pool was 4.7 days. Results are presented and discussed in relation to the absolute values of 13C fixed and allocated within the plant,soil system. [source]

Increase in the fracture toughness and bond energy of clay by a root exudate

Effect of root mucilage and modelled root exudates on soil structure

EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2000
O. Traoré
Summary Plant roots release in the rhizosphere diverse organic materials which may have different effects on soil structure. We have evaluated the effect of natural and modelled root-released materials on soil aggregates and the biodegradation of carbon from roots in the soil. The effects of root mucilage from maize and of a modelled soluble exudate were compared with those of simple compounds (glucose, polygalacturonic acid). For all treatments, soil was amended with 2 g C kg,1 soil and incubated for 30 days at 25°C. The biodegradation of mucilage was similar to that of polygalacturonic acid, and slower than the decomposition of modelled exudates and glucose. Addition of all substrates increased the stability of aggregates, but the duration of this effect depended on the chemical nature of the material. Compared with the control, the proportion of stable aggregates after 30 days of incubation was multiplied by 3.8 for root mucilage, by 4.2 for modelled soluble exudates, by 2.5 for polygalacturonic acid and by 2.0 for glucose. The different fractions of root exudates in the rhizosphere evidently affected the aggregate stability. [source]

Chemotactic response of plant-growth-promoting bacteria towards roots of vesicular-arbuscular mycorrhizal tomato plants

FEMS MICROBIOLOGY ECOLOGY, Issue 3 2003
Sushma Gupta Sood
Abstract The chemotactic responses of the plant-growth-promoting rhizobacteria Azotobacter chroococcum and Pseudomonas fluorescens to roots of vesicular-arbuscular mycorrhizal (Glomus fasciculatum) tomato plants were determined. A significantly (P=0.05) greater number of bacterial cells of wild strains were attracted towards vesicular-arbuscular mycorrhizal tomato roots compared to non-vesicular-arbuscular mycorrhizal tomato roots. Substances exuded by roots served as chemoattractants for these bacteria. P. fluorescens was strongly attracted towards citric and malic acids, which were predominant constituents in root exudates of tomato plants. A. chroococcum showed a stronger response towards sugars than amino acids, but the response was weakest towards organic acids. The effects of temperature, pH, and soil water matric potential on bacterial chemotaxis towards roots were also investigated. In general, significantly (P=0.05) greater chemotactic responses of bacteria were observed at higher water matric potentials (0, ,1, and ,5 kPa), slightly acidic to neutral pH (6, 6.5 and 7), and at 20,30°C (depending on the bacterium) than in other environmental conditions. It is suggested that chemotaxis of P. fluorescens and A. chroococcum towards roots and their exudates is one of the several steps in the interaction process between bacteria and vesicular-arbuscular mycorrhizal roots. [source]

Seasonal variation in rates of methane production from peat of various botanical origins: effects of temperature and substrate quality

FEMS MICROBIOLOGY ECOLOGY, Issue 3 2000
Inger Bergman
Abstract The methane produced in peat soils can vary over the growing season due to variations in the supply of available substrate, the activity of the microbial community or changes in temperature. Our aim was to study how these factors regulate the methane production over the season from five different peat types of different botanical origin. Peat samples were collected on seven occasions between June and September. After each sampling, the peat soils were incubated at five different temperatures (7, 10, 15, 20 and 25°C) without added substrate, or at 20°C with added substrate (glucose, or H2/CO2, or starch). Rates of methane production averaged over the season differed significantly (P<0.05, R2=0.76) among the five peat types, the minerotrophic lawn producing the highest rates, and the hummock peat producing the lowest. The seasonal average Q10 values for each plant community varied between 4.6 and 9.2, the highest value being associated with the ombrotrophic lawn and the lowest value with the mud-bottom plant community. For the unamended peat samples, the rates of methane production from each plant community varied significantly (P<0.05) over the season. This implies that the quality of organic matter, in combination with changes in temperature, explains the seasonal variation in methane production. However, addition of saturating amounts of glucose, H2/CO2 or starch at 20°C significantly reduced the seasonal variation (P<0.05) in methane production in peat from the minerotrophic lawn, wet carpet and mud-bottom plant communities. This suggests that substrate supply (e.g. root exudates) for the micro-organisms also varied over the season at these sites. Seasonal variation in methane production rates was apparent in peat from the hummock and ombrotrophic lawn plant communities even after addition of substrates, suggesting that the active biomass of the anaerobic microbial populations at these sites was regulated by other factors than the ones studied. [source]

Establishment of Azotobacter on plant roots: chemotactic response, development and analysis of root exudates of cotton (Gossypium hirsutum L.) and wheat (Triticum aestivum L.)

Phytoremediation: the state of rhizosphere ,engineering' for accelerated rhizodegradation of xenobiotic contaminants

JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 3 2007
E. Kudjo Dzantor
Abstract Phytoremediation has emerged as the method of choice for cleaning up a broad range of environmental contaminants. One process through which plants render some xenobiotic organic contaminants innocuous in soil involves plant,microbe interactions in which root exudates stimulate entire microbial communities, or induce specific enzymes in competent individuals to cause enhanced rhizodegradation. For some contaminants these inherent processes can be slow; however, potentials exist for their improvement through rhizosphere manipulations. Although this requires a greater understanding than currently exists with respect to plant and microbe components and interactions involved in the biodegradation of xenobiotic contaminants, improved understanding is being achieved by advances in biochemical and molecular characterization, and visualization of rhizosphere phenomena. In combination with earlier knowledge of naturally-occurring plant,microbe interactions such as the opine concept, this new knowledge considerably improves the opportunities for manipulating rhizosphere interactions to greatly accelerate rhizodegradation for routine practical implementation in the field. Copyright © 2007 Society of Chemical Industry [source]

Bioassay and Identification of Root Exudates of Three Fruit Tree Species

Induction of Phenolic Compounds in Pea (Pisum sativum L.) Inoculated by Rhizobium leguminosarum and Infected with Orobanche crenata

JOURNAL OF PHYTOPATHOLOGY, Issue 11-12 2007
Y. Mabrouk
Abstract Parasitic plants are among the most important problematic weeds, they are responsible of major losses of many crops. Early growth stages, such as seed germination stimulated by host root exudates and tubercle development, are key phases for these parasites development. Inhibition of these early phases could be a general strategic option for parasitic plants management. In our previous study, we have demonstrated that some Rhizobium leguminosarum strains decrease pea infection by Orobanche crenata and germinated seeds enhanced browning symptoms. These observations suggested the probability of toxic compounds accumulation such as gallic acid and naringenin used as a defence strategy by inoculated pea plants. In this study, we demonstrate that these two phenolic compounds cause severe physiological disorder of germination broomrape seeds. They inhibited germination of O. crenata seeds induced by strigol analogue GR24, and caused a browning reaction in germinated seeds. [source]

Technique for visual demonstration of germinating arbuscular mycorrhizal spores and their multiplication in pots

JOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 5 2007
Jitendra Panwar
Abstract We describe a simple technique for the germination of arbuscular mycorrhizal (AM),fungal spores and their multiplication in pots. Glomus fasciculatum, G. mosseae, and Gigaspora margarita were used. A single wheat seedling was tied to a glass slide, previously covered with filter paper with the help of thread. One single surface-sterilized AM-fungal spore was placed on the middle portion of the root of the wheat seedling using a sterilized syringe. The slide was placed vertically in a 100,mL glass beaker filled with 25,mL of root exudates,water (1:4, v/v) solution, which was collected by growing twenty wheat seedlings in a 150,mL beaker filled with 100,mL sterilized distilled water for 7 d. The slide was observed daily using a compound microscope to follow the time course of germination. In this technique, the spore is directly in contact with the host root, and a visualization of spore germination, hyphal development, and appressorium formation is possible without disrupting fungal growth or the establishment of the symbiosis. The method allows to document the germination events and to assess hyphal-elongation rates by photographing the same spore on consecutive days. The inoculated seedling was used to initiate single-spore multiplication in a sterilized (autoclave on 3 alternate days at 120°C for 120,min at 1.05,kg,cm,2 pressure) potted sandy soil (150,mL volume) into which the slide with the inoculated seedling was inserted carefully through a previously made slit. The wheat seedlings in all pots (4 treatments and 15 replications) became colonized by mycorrhiza, confirming that the establishment of the AM-fungal symbiosis is highly reproducible. Our technique permits the relatively undisturbed growth of the symbiotic partners, the visualization of germinating AM-fungal spores, and their multiplication in pots. This simple and low-cost method facilitates the production of pure lines of AM fungi from single spores, allowing for the study of intraspecific variation and potentiality for cytological, biochemical, physiological, and taxonomical studies. [source]

Confirmation and determination of carboxylic acids in root exudates using LC,ESI-MS

JOURNAL OF SEPARATION SCIENCE, JSS, Issue 15 2007
Zuliang Chen
Abstract Reversed-phase liquid chromatography with UV detection is of limited applicability in the separation and identification of carboxylic acids because of the column's poor separation efficiency and the non-selective nature of the UV detector. To address this issue, RP-LC with electrospray ionization mass spectrometry has been explored for the confirmation and determination of carboxylic acids in plant root exudates, with ESI-MS providing structural information, high selectivity, and high sensitivity. The separation of 10 carboxylic acids (pyruvic, lactic, malonic, maleic, fumaric, succinic, malic, tartaric, trans -aconitic, and citric acid) was performed on a C18 column using an eluent containing 0.1% (v/v) acetic acid within 10 min, where the acidic eluent not only suppressed the ionization of the carboxylic acids to be retained on the column, but was also compatible with ESI-MS detection. In addition, an additional standard was used to overcome the matrix effect. The results showed that peak areas correlated linearly with the concentration of carboxylic acids over the range 0.05,10 mg/L. The detection limits of target acids (signal-to-noise S/N ratio of 3) ranged from 20 to 30 ,g/L. Finally, the proposed method was used for the confirmation and determination of low-molecular-weight carboxylic acids in plant root exudates, and provided a simple analytical procedure, including sample processing, fast separation, and high specificity and sensitivity. [source]

Carboxylate composition of root exudates does not relate consistently to a crop species' ability to use phosphorus from aluminium, iron or calcium phosphate sources

NEW PHYTOLOGIST, Issue 1 2007
Stuart J. Pearse
Summary ,,The relationship between carboxylate release from roots and the ability of the species to utilize phosphorus from sparingly soluble forms was studied by comparing Triticum aestivum, Brassica napus, Cicer arietinum, Pisum sativum, Lupinus albus, Lupinus angustifolius and Lupinus cosentinii. ,,Plants were grown in sand and supplied with 40 mg P kg,1 in the sparingly soluble forms AlPO4, FePO4 or Ca5OH(PO4)3, or as soluble KH2PO4; control plants received no P. ,,The ability to utilize sparingly soluble forms of P differed between forms of P supplied and species. Pisum sativum and C. arietinum did not access AlPO4 or FePO4 despite releasing carboxylates into the rhizosphere. ,,Species accessed different forms of sparingly soluble P, but no species was superior in accessing all forms. We conclude that a single trait cannot explain access to different forms of sparingly soluble P, and hypothesize that in addition to carboxylates, rhizosphere pH and root morphology are key factors. [source]

Two mire species respond differently to enhanced ultraviolet-B radiation: effects on biomass allocation and root exudation

NEW PHYTOLOGIST, Issue 4 2006
Riikka Rinnan
Summary ,,Increased ultraviolet-B (UV-B) radiation arising from stratospheric ozone depletion may influence soil microbial communities via effects on plant carbon allocation and root exudation. ,,Eriophorum angustifolium and Narthecium ossifragum plants, grown in peatland mesocosms consisting of Sphagnum peat, peat pore water and natural microbial communities, were exposed outdoors to enhanced UV-B radiation simulating 15% ozone depletion in southern Scandinavia for 8 wk. ,,Enhanced UV-B increased rhizome biomass and tended to decrease the biomass of the largest root fraction of N. ossifragum and furthermore decreased dissolved organic carbon (DOC) and monocarboxylic acid concentration, which serves as an estimate of net root exudation, in the pore water of the N. ossifragum mesocosms. Monocarboxylic acid concentration was negatively related to the total carbon concentration of N. ossifragum leaves, which was increased by enhanced UV-B. By contrast, enhanced UV-B tended to increase monocarboxylic acid concentration in the rhizosphere of E. angustifolium and its root : shoot ratio. Microbial biomass carbon was increased by enhanced UV-B in the surface water of the E. angustifolium mesocosms. ,,Increased UV-B radiation appears to alter below-ground biomass of the mire plants in species-specific patterns, which in turn leads to a change in the net efflux of root exudates. [source]

Root exudates of the hyperaccumulator Thlaspi caerulescens do not enhance metal mobilization

Isolation and identification of a potent allelopathic substance in rice root exudates

PHYSIOLOGIA PLANTARUM, Issue 3 2002
Hisashi Kato-Noguchi
A search for growth inhibitors in rice root exudates was undertaken in order to clarify the allelopathic system in rice (Oryza sativa L.). Rice seedlings inhibited the growth of cress (Lepidium sativum L.) and lettuce (Lactuca sativa L.) seedlings when the cress and lettuce were grown with rice seedlings. The putative compound causing the inhibitory effect of rice seedlings was isolated from their culture solution, and the chemical structure of the inhibitor was determined by spectral data as momilactone B. Momilactone B inhibited the growth of cress and lettuce seedlings at concentrations greater than 3 and 30 µM, respectively. The concentration of momilactone B was 3.4 and 1.1 nmol per seedling in the culture solutions of husked and non-husked rice seedlings, respectively. These results suggest that rice seedlings may release momilactone B into the environment and the stress caused by the husk-treatment may increase the amount of momilactone B released. Thus, momilactone B may play an important role in rice allelopathy. [source]

Low molecular weight organic acids and fatty acids in root exudates of two Lupinus cultivars at flowering and fruiting stages

PHYTOCHEMICAL ANALYSIS, Issue 5 2001
J. A. Lucas García
Abstract Low molecular weight organic acids (LOAs) and fatty acids in root exudates of two lupin cultivars, Lupinus albus cv. Multolupa and L. luteus cv. Tremosilla, were determined at flowering and fruiting stages. LOAs were analysed by capillary electrophoresis. Acetic and citric acids were the most abundant, especially the latter in L. luteus at the flowering stage (5922.79,µg/g dry root). The significant decrease in acid content of both cultivars from flowering to fruiting stages was also striking. The highest levels of acetic acid were detected in L. luteus at fruiting stage (1542.03,µg/g dry root). The significant citrate production in L. luteus could be related to the low phosphorus concentration in the studied soils but not to proteoid roots, which were detected only in L. albus. The source of the LOAs detected in these exudates is also discussed, since they may be produced either by the plant or by the associated rhizobacteria. The profile of phospholipid fatty acids was determined by high-resolution GC. A high level of 18:2,6 (a fatty acid specific to fungi) was found in exudates of L. luteus (a mycorrhizal plant) in contrast to L. albus (a non-mycorrhizal plant). Copyright © 2001 John Wiley & Sons, Ltd. [source]

Relationship between boron and calcium in the N2 -fixing legume,rhizobia symbiosis

PLANT CELL & ENVIRONMENT, Issue 11 2003
M. REDONDO-NIETO
ABSTRACT Because boron (B) and calcium (Ca2+) seem to have a strong effect on legume nodulation and nitrogen fixation, rhizobial symbiosis with leguminous plants, grown under varying concentrations of both nutrients, was investigated. The study of early pre-infection events included the capacity of root exudates to induce nod genes, and the degree of adsorption of bacteria to the root surface. Both phenomena were inhibited by B deficiency, and increased by addition of Ca2+, resulting in an increase of the number of nodules. The infection and invasion steps were investigated by fluorescence microscopy in pea nodules harbouring a Rhizobium leguminosarum strain that constitutively expresses green fluorescent protein. High Ca2+ enhanced cell and tissue invasion by Rhizobium, which was highly inhibited after B deficiency. This was combined with an increased B concentration in nodules of plants grown on B-free medium and supplemented with high Ca2+ concentrations, and that can be attributed to an increased B import to the nodules. Histological examination of indeterminate (pea) and determinate (bean) nodules showed an altered nodule anatomy at low B content of the tissue. The moderate increase in nodular B due to additional Ca2+ was not sufficient to prevent the abnormal cell wall structure and the aberrant distribution of pectin polysaccharides in B-deficient treatments. Overall results indicate that the development of the symbiosis depends of the concentration of B and Ca2+, and that both nutrients are essential for nodule structure and function. [source]

Exudates as a fallback food for Callimico goeldii

AMERICAN JOURNAL OF PRIMATOLOGY, Issue 2 2009
Leila M. Porter
Abstract Fallback foods have been defined as resources for which a species has evolved specific masticatory and digestive adaptations, and are consumed principally when preferred foods are scarce. In the present field investigation, we examine fungi, fruit, and exudate consumption in one group of Callimico goeldii in order to determine the importance of exudates as a fallback food for this species. Based on a total of 1,198,hr of quantitative behavioral data collected between mid-November 2002,August 2003, we found that pod exudates of Parkia velutina accounted for 19% of callimico feeding time in the dry season. This resource was not consumed in the wet season when fruits and fungi were the most common items in the diet. In the dry season of 2005 (July), the same callimico study group did not consume Parkia pod exudates. Instead, the group ate exudates obtained from holes gouged in tree trunks by pygmy marmosets and exudates resulting from natural weathering and insect damage on trunks, roots, and lianas. Pod exudates are reported to contain greater amounts of readily available energy than do trunk and root exudates, and were consumed throughout all periods of the day, particularly in the late afternoon. Trunk and root exudates were consumed principally in the morning. We propose that digestive adaptations of the hindgut, which enable callimicos to exploit fungi (a resource high in structural carbohydrates) year-round, predispose them to efficiently exploit and process exudates as fallback foods when other resources, such as ripe fruits, are scarce. Am. J. Primatol. 71:120,129, 2009. © 2008 Wiley-Liss, Inc. [source]