Showing papers on "Root hair published in 1992"

Depolarization of alfalfa root hair membrane potential by Rhizobium meliloti Nod factors

Abstract: Although much is known about the bacterial genetics of early nodulation, little is known about the plant cell response. Alfalfa root hair cells were impaled with intracellular microelectrodes to measure a membrane potential depolarizing activity in Rhizobium meliloti cell-free filtrates, a plant response dependent on the bacterial nodulation genes. The depolarization was desensitized by repeated exposure to factors and was not observed in a representative nonlegume. A purified extracellular Nod factor, NodRm-IV(S), caused membrane potential depolarization at nanomolar concentrations. This rapid single-cell assay provides a tool for dissecting the mechanisms of host cell response in early nodulation.

Induction of Pre-Infection Thread Structures in the Leguminous Host Plant by Mitogenic Lipo-Oligosaccharides of Rhizobium

Abstract: Root nodules of leguminous plants are symbiotic organs in which Rhizobium bacteria fix nitrogen. Their formation requires the induction of a nodule meristem and the formation of a tubular structure, the infection thread, through which the rhizobia reach the nodule primordium. In the Rhizobium host plants pea and vetch, pre-infection thread structures always preceded the formation of infection threads. These structures consisted of cytoplasmic bridges traversing the central vacuole of outer cortical root cells, aligned in radial rows. In vetch, the site of the infection thread was determined by the plant rather than by the invading rhizobia. Like nodule primordia, pre-infection thread structures could be induced in the absence of rhizobia provided that mitogenic lipo-oligosaccharides produced by Rhizobium leguminosarum biovar viciae were added to the plant. In this case, cells in the two outer cortical cell layers containing cytoplasmic bridges may have formed root hairs. A common morphogenetic pathway may be shared in the formation of root hairs and infection threads.

Rhizobium meliloti produces a family of sulfated lipooligosaccharides exhibiting different degrees of plant host specificity.

Abstract: We have shown that a Rhizobium meliloti strain overexpressing nodulation genes excreted high amounts of a family of N-acylated and 6-O-sulfated N-acetyl-beta-1,4-D-glucosamine penta-, tetra-, and trisaccharide Nod factors. Either a C(16:2) or a C(16:3) acyl chain is attached to the nonreducing end subunit, whereas the sulfate group is bound to the reducing glucosamine. One of the tetrasaccharides is identical to the previously described NodRm-1 factor. The two pentasaccharides as well as NodRm-1 were purified and tested for biological activity. In the root hair deformation assay the pentasaccharides show similar activities on the host plants Medicago sativa and Melilotus albus and on the non-host plant Vicia sativa at a dilution of up to 0.01-0.001 microM, in contrast to NodRm-1, which displays a much higher specific activity for Medicago and Melilotus than for Vicia. The active concentration range of the pentasaccharides is more narrow on Medicago than on Melilotus and Vicia. In addition to root hair deformation, the different Nod factors were shown to induce nodule formation on M. sativa. We suggest that the production of a series of active signal molecules with different degrees of specificity might be important in controlling the symbiosis of R. meliloti with several different host plants or under different environmental conditions.

A 2-O-methylfucose moiety is present in the lipo-oligosaccharide nodulation signal of Bradyrhizobium japonicum

Abstract: Bradyrhizobium japonicum is a soil bacterium that forms nitrogen-fixing nodules on the roots of the agronomically important legume soybean. Microscopic observation of plant roots showed that butanol extract of B. japonicum strain USDA110 cultures induced for nod gene expression elicited root hair deformation, an early event in the nodulation process. The metabolite produced by B. japonicum responsible for root hair deformation activity was purified. Chemical analysis of the compound revealed it to be a pentasaccharide of N-acetylglucosamine modified by a C18:1 fatty acyl chain at the nonreducing end. In these respects, the B. japonicum metabolite is similar to the lipo-oligosaccharide signals described from Rhizobium species. However, the B. japonicum compound is unique in that an additional sugar, 2-O-methylfucose, is linked to the reducing end. Comparative analysis of the B. japonicum Nod metabolite and those characterized from Rhizobium species suggests that the presence of the fucosyl residue plays an important role in the specificity of the B. japonicum-soybean symbiosis. The availability of the purified B. japonicum nodulation signal should greatly facilitate further studies of soybean nodulation.

Calcium influx at the tip of growing root-hair cells of Arabidopsis thaliana.

Abstract: The role of extracellular Ca2+ in root-hair tip growth has been investigated in Arabidopsis thaliana (L.) Heynh. Root-hair length was found to be dependent on the concentration of Ca2+ in the growth medium, with maximum length achieved at [Ca2+] of 0.3–3.0 mM. Using a non-intrusive calcium-specific vibrating microelectrode, an extracellular Ca2+ gradient was detected at the tips of individual growing root-hair cells. The direction of the gradient indicated a net influx of Ca2+ into root-hair cells. No gradient was detected near the sides of the root hairs or at the tips of non-growing root hairs. When root hairs were exposed to the Ca2+-channel blocker nifedipine, tip growth stopped and the extracellular Ca2+ gradient was abolished. These results indicate that Ca2+ influx through plasma-membrane Ca2+ channels is required for normal root-hair tip growth.

Molecular mechanisms of attachment of Rhizobium bacteria to plant roots.

Abstract: Attachment of bacteria to plant cells is one of the earliest steps in many plant-bacterium interactions. This review covers the current knowledge on one of the best-studied examples of bacterium-plant attachment, namely the molecular mechanism by which Rhizobium bacteria adhere to plant roots. Despite differences in several studies with regard to growth conditions of bacteria and plants and to methods used for measuring attachment, an overall consensus can be drawn from the available data. Rhizobial attachment to plant root hairs appears to be a two-step process. A bacterial Ca(2+)-binding protein, designated as rhicadhesin, is involved in direct attachment of bacteria to the surface of the root hair cell. Besides this step, there is another step which results mainly in accumulation and anchoring of the bacteria to the surface of the root hair. This leads to so-called firm attachment. Depending on the growth conditions of the bacteria, the latter step is mediated by plant lectins and/or by bacterial appendages such as cellulose fibrils and fimbriae. The possible role of these adhesions in root nodule formation is discussed.

Effects of agrochemicals and heavy metals on fast-growing rhizobia and their symbiosis with small-seeded legumes

Abstract: The effect of potentially hazardous agrochemicals including fungicides, herbicides and heavy metals on symbiotic nitrogen fixation have been investigated. The substances were tested with eight rhizobial strains from three cross-inoculation groups: Rhizobium leguminosarum b.v. trifolii, R. meliloti and R. loti in pure culture studies. Bacteria were obtained from a culture collection or from soils. Sensitivity of the bacteria to the agrochemicals and heavy metals varied. None of the bacteria were tolerant to all chemicals. No difference in tolerance between cross-inoculation groups existed. Bacteria were able to multiply at concentrations of agrochemicals equal to or higher than recommended field-application rates. Heavy metals concentrations that severely inhibited growth were far lower than the highest amounts allowed under the current Commission of the European Communities' guidelines for environmental protection. Bacterial growth in presence of the agrochemicals and heavy metals, apart from glyphosate and zinc, did not influence nodulation ability of the strains. Development of uninoculated plants was inhibited at increasing concentrations of all compounds, red clover being most sensitive. Herbicides were most harmful, with injuries occurring at levels 1 10 - 1 10,000 of recommended applied concentrations. Uninoculated plants were less tolerant to agrochemicals, but were more tolerant to heavy metals compared to the bacteria. Root hair deformations similar to bacterial-induced root hair deformations were induced by bentazone, chlorsulphuron and monochlorophenoxyacetic acid on uninoculated plants. Symbiotic interactions were adversely affected by several of the agrochemicals. Bacterial-induced root hair deformations necessary for nodulation decreased in the presence of benomyl, bentazone, chlorsulphuron, fenpropimorph, mancozeb and monochlorophenoxyacetic acid. Fenpropimorph and mancozeb did not cause root hair deformations at increasing concentrations, indicating that these may inhibit nodulation under field conditions. Nodule development was inhibited at increased levels of bentazone, chlorsulphuron, glyphosate and mancozeb. Dry matter production of nodulated plants was adversely affected by bentazone and chlorsulphuron, indicating disturbances in nodule function.

Stimulatory effects of jasmonic acid on potato stem node and protoplast culture

Abstract: The effect of jasmonic acid (JA), in a wide range of concentrations (0.01–100 μM), on the development of potato plantlets (Solanum tuberosum L.cv. Vesna) was investigated in order to discriminate between physiological and supraoptimal effects of this growth regulator in vitro. Concentrations from 0.1–1 μM significantly increased the length of developed plants. Application of JA in these concentrations resulted in a very well differentiated root system with many lateral branches. With increasing JA concentrations, the main roots shortened and thickened. Concentrations higher than 10 μM led to the compaction of the stem, roots, and root hairs, giving a stunted appearance to the plants. The effect of JA on cell wall regeneration and callus formation was observed in potato leaf protoplast culture. JA at concentrations from 0.01–1 μM stimulated cell division and microcalli development.

Abscisic Acid Elicits the Water-Stress Response in Root Hairs of Arabidopsis thaliana

Abstract: Water stress has been shown to cause root hairs to become short and bulbous. Because abscisic acid (ABA) mediates a variety of water-stress responses, we investigated the response of Arabidopsis thaliana root hairs to ABA. When wild-type root hairs were treated with ABA, they exhibited the water-stress response. The Arabidopsis mutants abi1 and abi2, which are insensitive to ABA at the seedling stage, did not display the root hair response. These data suggest that ABA may mediate the response of root hairs to water stress. The drought response of root hairs resulting in an inhibition of tip growth will provide an easy screen to select mutations that are insensitive to ABA and/or involved in tip growth.

Immunofluorescent Localization of Plasma Membrane H+-ATPase in Barley Roots and Effects of K Nutrition

Abstract: The plasma membrane H+-ATPase (PM-H+-ATPase) of barley (Hordeum vulgare L cv Klondike) roots was assayed by cross-reaction on western blots and cryosections with an antibody against the PM-H+-ATPase from corn roots Under conditions of reduced K availability, which have previously been shown to increase K influx by greater than 25-fold, there were only minor changes detected in PM-H+-ATPase levels Antibody labeling of cryosections showed the relative distribution of PM-H+-ATPase among cell types in root tips and mature roots Epidermal cells, both protoderm and mature root epidermis, including root hairs, had high levels of antibody binding In mature roots, the stelar tissue showing the highest antibody binding was the companion cells of the phloem, followed by pericycle, xylem parenchyma, and endodermis

The PsENOD12 Gene Is Expressed at Two Different Sites in Afghanistan Pea Pseudonodules Induced by Auxin Transport Inhibitors

Abstract: A number of early nodulin genes are expressed in specific cell types as pea (Pisum sativum) root nodules develop. The Pisum sativum early nodulin PsENOD2 is detected only in the uninfected cells of the nodule parenchyma, whereas PsENOD12 is expressed at two spatially removed sites: in root hairs and adjacent cortical cells, both of which can be invaded by Rhizobium entering through infection threads, and in derivatives of newly divided root inner cortical cells that establish the nodule primordium. We tested whether Rhizobium infection is required for triggering PsENOD12 gene expression by inducing nodule-like structures on Afghanistan pea roots with the auxin transport inhibitor N-(1-naphthyl)phthalamic acid (NPA). These nodule-like structures lack infection threads but resemble Rhizobium-induced nodules in other aspects. For one, both PsENOD2 and PsENOD12 transcripts were detected in these structures. PsENOD2 mRNA was localized by in situ hybridization to a zone equivalent to the nodule parenchyma of Rhizobium-induced nodules, whereas PsENOD12 transcripts were detected in a group of cells comparable to the nodule primordium of developing nodules. In addition, PsENOD12 mRNA was detected in uninfected root hairs 48 h after NPA treatment. These results indicate that infection is not a trigger for PsENOD12 gene expression in Afghanistan pea and rather suggest that the expression of the PsENOD2 and PsENOD12 genes is correlated with the differentiation of specific cell types in the developing nodule.

Production of the Phytoalexin Glyceollin I by Soybean Roots in Response to Symbiotic and Pathogenic Infection

Abstract: The amount of the phytoalexin glyceollin I in root exudate and root hairs of individual seedlings of Glycine max (L. Merr. cv. Preston) was analysed using a radioimmunoassay. Bradyrhizobium japonicum 110spc4, which is able to form nitrogen fixing nodules with this plant, caused an increase of up to 50-fold in glyceollin I levels in root exudate relative to uninfected control seedlings. Maximum glyceollin I levels were reached within 10 h of incubation. Elevated glyceollin I levels were also observed after incubation of soybean roots in sterile bacterial supernatant, a suspension of autoclaved bacteria or the supernatant from broken cells of Bradyrhizobium japonicum. Increased glyceollin I production is not due to the process of active root hair penetration by the microsymbiont since living bacterial cells are not necessary for the induction. The observed glyceollin I production in response to Bradyrhizobium japonicum is several times lower than that after pathogenic infection. Infection with zoospores of the phytopathogenic oomycete, Phytophthora megasperma f. sp. glycinea race 1, leads within 20 h to an accumulation of 7 nmol glyceollin I/seedling in the root exudate of the compatible cultivar Kenwood and 48 nmol glyceollin I/seedlings in that of the incompatible cultivar Maple Arrow. These results support the idea that phytoalexins are implicated in determination of compatibility in pathogenic interactions. Crude cell extracts of different symbiotic bacteria (Bradyrhizobium japonicum 110spc4, Rhizobium meliloti 2011, Rhizobium leguminosarum PRE 8, Sinorhizobium fredii HH 103) were found to induce different amounts of glyceollin I in the root exudate. The observed glyceollin I levels could not be correlated with the ability of these rhizobial strains to nodulate Glycine max. Inhibition of flavonoid and phytoalexin synthesis by (R)-(1-amino-2-phenylethyl)phosphonic acid (APEP), a specific inhibitor of the phenylalanine-ammonia-lyase (PAL), during the first 20 h of the symbiotic interaction dramatically decreased the number of nodules formed in root regions that had been in contact with the inhibitor. This effect was observed at concentrations that inhibited neither bacterial nor plant growth. The implications of these findings for the process of nodule initation are discussed.

Growth and Movement of Spot Inoculated Rhizobium meliloti on the Root Surface of Alfalfa

Abstract: Inoculum droplets of approximately 10 nanoliter volume and containing about 10 Rhizobium meliloti cells were placed onto the root surface of alfalfa seedlings in plastic growth pouches at either the root tip, the position of the smallest emergent root hairs, or at a site midway between these points. The droplets were initially confined to an area of about 0.2 square millimeter at the point of application. By 48 and 96 hours after inoculation, the inoculum bacteria and their progeny were distributed over several centimeters of the root between the initial site of deposition and the growing root tip, reaching densities of 10(3) to 10(4) bacteria per centimeter near the site of initial deposition and decreasing exponentially from that point toward the root tip. Graphite particles deposited on the root surface close to the growing tip were similarly distributed along the root length by 48 and 96 hours, suggesting that passive displacement by root cell elongation was primarily responsible for the spread of bacteria. A nonmotile mutant of R. meliloti colonized alfalfa roots to the same extent as the wild type and was usually distributed in the same manner, indicating that bacterial motility contributed little under these conditions to long distance spread of the bacteria. However, when applied in low numbers, R. meliloti mutants defective in motility or chemotaxis were considerably less efficient in initiating nodules near the point of inoculation than the wild type. This implies that motility and/or chemotaxis contribute significantly to local exploration for suitable infection sites. Almost all nodules on the primary root formed within a few millimeters of the spot-inoculation site, indicating that, under our experimental conditions, movement and multiplication of R. meliloti on the root surface were not sufficient to maintain an adequate population in the infectible region of the root during root growth.

Phenotypic characterization of sym8 and sym9, two genes conditioning non-nodulation in Pisum sativum 'Sparkle'

Abstract: Two non-nodulating and non-allelic mutants of P. sativum (L.) 'Sparkle', R25 (sym8) and R72 (sym9), were obtained by γ-radiation. Non-nodulation in each mutant was conditioned by a single recessive gene. Growth analysis indicated that if the mutants were provided with adequate fixed nitrogen, they both had the same growth rate as their nodulating parent, 'Sparkle'. Reciprocal grafts between mutants and parent plants indicated that non-nodulation was controlled by the root genotype. Both mutants induced the common nod genes in rhizobia, and had either higher or similar numbers of rhizobia attached to their roots as had 'Sparkle'. Microscopic studies indicated that root hairs of R72 deformed after inoculation, whereas root hairs of R25 did not show such deformation. In both mutants hair curling, infection thread formation, and nodule meristem initiation did not occur. Key words: mutants, sym genes, nodulation stages, symbiosis.

Consequences of in vitro and ex vitro root initiation for miniature rose production

Abstract: Microshoots of Rosa chinensis var. minima (cvs Debut, Ginny, Red Ace and Tipper) were rooted using standardized in vitro and ex vitro root initiation techniques, then comparatively examined with regard to anatomical and morphological root character and effect of root initiation treatment on later plant development. After 18 days of in vitro or ex vitro rooting treatment, comparable rooting ranging from 95-100% was obtained for three of the four cultivars. Ex vitro rooting promoted longer roots and a tendency for both higher root number and area. Ex vitro roots were flexible, white, and produced branch roots while in vitro roots were brittle, darkened and did not branch. Cross sectional data revealed that ex vitro roots were thinner, possessed root hairs, and tended to have greater vascular area to root area with advanced development of the vascular tissue than in vitro- produced roots. Ex vitro-rooted plants of all cultivars except ‘Ginny’ had greater root growth (area and dry mass) and shoot growth (heig...

Ontogeny of synthesized Picea abies (L.) Karst.–Hebeloma crustuliniforme (Bull. ex St Amans) Quél. ectomycorrhizas

Abstract: summary Ectomycorrhizas were synthesized between Picea abies (L.) Karst. and Hebeloma crustuliniforme (Bull. ex St Amans) Quel. in growth pouches containing activated charcoal filter paper. Immediately emanating hyphae from inoculated plugs contacted root hairs and root surfaces, hyphal morphology was altered. They became short-celled with few clamp connections, highly branched, and lacked cell wall ornamentation. Then, hyphae on root surfaces formed an inner synenchymatous mantle and loose hyphae formed an outer prosenchymatous mantle. Simultaneously, root cap cells became invaded by fungal hyphae and their remnants were incorporated into the inner mantle. Further root elongation took place but root hair production was suppressed. Thirdly, a Hartig net began to form in basal portions of developing ectomycorrhizas and the fungal mantle became denser and thicker. Fourthly, growth of the root was reduced and the hyphae of the Hartig net penetrated between cortical cells moving toward the apex. Fifthly, metacutis occasionally surrounded the meristem. At this stage the formation of the ectomycorrhiza can be considered to be complete and the rootlet itself is temporarily in a dormant state.

Chronology and mechanisms of P uptake by mycorrhizal sweet potato plants

Abstract: summary Vesicular-arbuscular (VA) mycorrhizal and non-mycorrhizal sweet potato plants [Ipomoea batatas (L.S) Lam. cv. White Star] were grown in a glasshouse in a phosphorus (P)-fixing soil in order to (i) establish the chronology of mycorrhiza-mediated P uptake, (ii) document the distribution of total and metabolically active external hyphae in relation to roots, root hairs and P-depletion zones at the time when the P-uptake response first becomes apparent, (iii) evaluate the pore-size distribution of the soil relative to the radii of roots, root hairs and hyphae of mycorrhizal fungi, and (iv) determine if sweet potato mycorrhiza alter the organic acid composition of the rhizosphere. Phosphorus inflow, VA mycorrhizal root colonization, and active hyphae increased during the first half of an 8 wk experiment. During the latter half of the experiment, however, colonization and active hyphae increased while P inflow decreased. Roots colonized by mycorrhizal fungi supported a higher proportion of active hyphae in the soil than non-colonized roots. In a second experiment, hyphal distribution around individual roots colonized by mycorrhizal fungi was not consistently different from hyphal distribution around non-colonized roots. Hyphae of mycorrhizal fungi were of a diameter that would allow them to penetrate pores that hold water at water contents less than field capacity while roots, and to a large extent root hairs, would be excluded from these pores. We found no evidence that sweet potato roots, whether or not they were colonized by mycorrhizal fungi, altered the organic acid composition of the rhizosphere. We conclude that mycorrhiza mediated P uptake commenced with the onset of colonization by the fungi and was due to a change in the ability of the root to come into contact with the soil solution.

Proteins Associated with Root-Hair Deformation and Nodule Initiation in Vigna unguiculata

Abstract: Developmental changes in the synthesis of root-hair proteins were followed in the symbiosis between the promiscuous legume Vigna unguiculata and the broad host-range Rhizobium sp. NGR234. Comparison of the two-dimensional electrophoresis patterns of proteins isolated from root hairs inoculated with wildtype or hair-deformation minus mutants revealed 12 symbiosis-specific proteins. Synthesis of three of these proteins was repressed 4 days after inoculation with Rhizobium. The remaining nine proteins were induced by Rhizobium 1, 2, or 4 days after inoculation. As three of these (15-, 31-, and 44-kDa hadulins) were specifically and transiently expressed in root hairs during the deformation process, we have named them hadulins (hair-deformation specific proteins). Five proteins (including 15- and 31-kDa hadulins) were first observed 24 hr after inoculation. Of these, only the 15-kDa hadulin was not induced by R. fredii USDA257Sl Nod⁺, Fix⁺ on V. unguiculata. Two days after inoculation, three additional proteins became apparent, while another (44-kDa hadulin) appeared on day 4. All 12 proteins seem to be associated with root-hair deformation and nodule development.

Scanning Electron Microscopy for Studying Root Morphology and Anatomy in Alfalfa Autotoxicity

Abstract: The aquous extract of alfalfa (Medicago sativa L.) shoots inhibits root elongation, shoot elongation, and/or germination of alfalfa itself―a phenomenon termed autotoxicity. The study of the mode of action of allelopathic and/or autotoxic compounds at the plant organ and cellular levels is limited by the depth of field, resolution, and magnification of a light microscope compared to a scanning electron microscope. Scanning electron microscopy techniques were used to study the morphology and anatomy of the roots inhibited by the shoot-aqueous-extract-inhibited, 5-d old WL-316' alfalfa roots revealed a 46% reduction in density and 54% reduction in length of root hairs compared to the control (...)

Root hair infection by Plasmodiophora brassicae in clubrootresistant and susceptible genotypes of Brassica oleracea, B. rapa and B. napus

Abstract: The pathogenesis of clubroot, a disease of cruciferous crops caused by the fungusPlasmodiophora brassicae, starts with infection of the root hairs. This process was studied in 13 accessions ofBrassica oleracea, B. napus and B. rapa with varying levels of plant resitance toP. brassicae. Seedlings were grown in a mineral solution, inoculated with resting spores ofP. brassicae, and the number of plasmodia developing in root hairs was recorded. When compared with the standard susceptible cultivar Septa, both higher and lower resistance to root hair infection was found in the accessions of the differentBrassica species. No complete resistance to root hair infection was found. Over the accessions studied, there was no correlation between the plant resistance estimated from greenhouse tests and the resistance to root hair infection of seedlings. The resistance of all accessions must at least partly be caused by other mechanisms which operate after the root hair plasmodia are formed.

Hormone-Resistant Mutants of Arabidopsis Have an Attenuated Response to Agrobacterium Strains

Abstract: We have examined the response of the hormone-resistant mutants axr1 and axr2 of Arabidopsis thaliana to inoculation by Agrobacterium tumefaciens and Agrobacterium rhizogenes. Our results indicate that recessive mutations in the axr1 gene affect the frequency of tumor formation after inoculation with either Agrobacterium strain. In addition, tumors produced on axr1 plants were smaller than those growing on wild-type plants. These results indicate that the product of the AXR1 gene is important for both crown gall and hairy root tumor formation. In contrast, the dominant axr2 mutation has a more severe effect on the development of crown gall tumors than on hairy root tumors. Crown gall tumors produced on axr2 plants had a different morphology than wild-type tumors and did not grow when they were removed from the explant. In contrast, a large number of hairy root tumors were produced on wild-type and axr2 plants, and both types of tumors grew when they were removed from the explant. Like the roots of axr2 plants, roots produced on axr2 explants lacked root hairs.

Influence of hydroponic culture method on morphology and hydraulic conductivity of roots of honey locust.

Abstract: The morphology and hydraulic conductivity of root systems of Gleditsia triacanthos L. var. inermis Willd. (honey locust) grown hydroponically in sand and solution cultures were compared. Total root system length was similar in the two cultures. However, root systems grown in solution had longer primary roots, fewer lateral roots and root hairs, and a greater distance between the tip of the primary root and the junction of the youngest secondary root and the primary root than root systems grown in sand. Hydraulic conductivities of root systems grown hydroponically for 21 or 35 days in sand or solution culture were similar. These findings show that different methods of hydroponic culture can affect root morphology without altering root resistance to water transport.

Boletinellus merulioides alters root morphology of pinus densiflora without mycorrhizal formation

Abstract: A stimulatory effect of Boletinellus merulioides on the roots of Pinus densiflora was evaluated using pure culture synthesis. Seedlings of P. densiflora were inoculated with cultures of B. merulioides at high and low glucose levels. After 180 days, shoot weight was not enhanced over controls by inoculation with the fungus, but root weight was significantly increased and roots were highly branched. Short roots were dichotomously branched, lacked root hairs, and had an internal morphology similar to that of ectomycorrhizal rootlets. A loose weft of fungal hyphae surrounded the short roots, but did not penetrate the epidermis. Higher glucose levels further increased root weight and branching. Filtrates from liquidgrown cultures of B. merulioides and Pisolithus tinctorius were compared using high performance liquid chromatography. Both fungi produced measurable quantities of indole-3-acetic acid, the in-vitro production of which was enhanced by higher glucose levels.

Perspectives in Plant Cell Recognition: The Rhizobium trap: root hair curling in root–nodule symbiosis

Abstract: Introduction The root-nodule bacteria Rhizobium, Bradyrhizobium and Azorhizobium (collectively rhizobia) invade and nodulate the roots of their host plants via either wounds or root hairs. The choice is made by the host plant, e.g. the same rhizobial strain infects Vigna roots via root hairs and Arachis roots via wounds (Sen & Weaver, 1984), whereas another strain infects Parasponia via root epidermal cracks and Macroptilium via root hairs (Marvel et al ., 1985). Shortly before or during root invasion, rhizobia induce cell divisions in the root cortex, resulting in formation of a nodule primordium. Through infection threads (tip-growing tubular structures containing invading rhizobia) and/or between cortical cells the rhizobia migrate towards the growing primordium, are endocytosed by young nodule cells, and differentiate into dinitrogenfixing bacteroids (see also Brewin et al ., this volume). Rhizobial invasion of most agronomically important legumes such as pea ( Pisum sativum ), soybean ( Glycine max ) and bean ( Phaseolus vulgaris ) occurs through root hairs. Infection of a living plant cell is an unusual phenomenon in plant–bacteria interactions. Plants are open organisms. At many sites, the intercellular space of a plant is in direct contact with the environment, e.g. in stomata, hydathodes or wounds resulting from emergence of lateral roots. A plant is used to regular visits of (plant-associated) bacteria to its interior. Therefore, wound-infection by rhizobia is a normal phenomenon whereas root hair infection is special.

Disuse part remover for root vegetables

Abstract: PURPOSE:To remove root hair growing from root of a material during transporting of the material by installing a root hair remover for a material on a side of a series of conveying roll conveying materials in pushing the materials to one side with rotating each of the materials. CONSTITUTION:Each material E is pushed to one side and conveyed with being rotated by a series of conveying roll A composed of brush rolls 1 having inclined brushes 2. Root hairs grown from root part of the material are removed during conveying of the material by a root hair remover B installed along the conveying direction of the material in the series of conveying roll A.

An Analysis of Host Range Specificity Genes of Rhizobium as a Model System for Virulence Genes in Phytobacteria

Abstract: Microbes have long exploited plants as favourable niches for colonisation. The surfaces and intercellular spaces of leaves, vascular tissue (phloem and xylem), and the ecto- and endorhizospheres (root surface and intercellular spaces between root cortical cells, respectively) are colonised by microbes to varying extents (Agrios, 1988). About 80 species of bacteria are known to interact with plants either beneficially or detrimentally. The consequence of colonisation or penetration of the plant tissue varies from asymptomatic, to disease, to symbiosis and is influenced greatly by the environment. Products of photosynthesis, such as organic acids and sucrose, can provide energy sources for microbial growth. The roots are not only surrounded by a plethora of soil microbes but up to 40% of fixed carbon can be exported from root cells as organic chemicals or as cellular debris sloughed from the root cap (Lynch and Whipps, 1989). The soil, by comparison, offers a relatively nutrient-poor environment (Suslow, 1982). The cellular energy reserves of microbes bound to soil particles will influence the rapidity of their responsiveness to changes in their environment, for example, the passing of a growing root in their vicinity.

A histochemical study of saikosaponins

Abstract: The root of Bupleurum chinese and B.scorzonerifolium was examined histochemically in order to clarify the distribution of saikosaponins in various tissues and parts of the root. By means of qualitative and quantitative analyses, saikosaponins, the bioactive principles in the root, were found to be abundant in the cortex outside the cambium and very little in the xylem of the root. It was also found that the thinner root hairs had the highest contents of saikosaponins, but decreased towards the thicker root head.

Early cytological events in the infection of the root hairs of Trifolium repens by Rhizobium leguminosarum biovar trifolii observed by glass slide culture in living seedlings

Abstract: This report describes the early cytological events in the infection byRhizobium leguminosarum biovartrifolii of the root hairs ofTrifolium repens seedlings kept alive on agar medium in glass slide culture experiment. The infection threads bearing rhizobia were formed as soon as the epidermal cells began to emerge as root hairs. On the top of some of these infected emerging root hairs, there were smoky, cell-debris-like bodies, which appeared to be derived from the cell wall dug by rhizobia. Similar bodies were also observed in longer root hairs. None of the root hair cells along the length of the roots which contained infection threads were curled or distorted. A substantial number of pink-colored nodules were later formed on the roots with non-curled infected root hairs.