Plant Root Surface Research Articles

Quantifying the adsorption and uptake of CuO nanoparticles by wheat root based on chemical extractions

Extensive application of metal nanoparticles is attracting more attention because of their potential environmental risks. Many studies have focused on the uptake of metal nanoparticles (NPs) by plant, but the adsorption of nanoparticles on root surface is often mistakenly regarded as their uptake. This study optimized the methods to distinguish the adsorption and uptake of CuO-NPs on the wheat root by applying différent metal competing ions (Na +, Mg 2+, and La 3+), surfactant (i.e., sodium dodecyl benzene sulfonate, SDBS), or complexing agents like NaOAc and Na 4EDTA, as well as ultrasonic technique. The results indicated that some CuO-NPs is strongly adsorbed on the plant root surface, and part of them by mechanical adhesion. Competing ions could not desorb the CuO-NPs from the root surface, while NaOAc and Na 4EDTA well dissolved the adsorbed CuO-NPs. In addition, the uptake and adsorption of CuO-NPs increased with increasing exposure concentrations of CuO-NPs in the range of 5–200 mg/L. The amount of CuO-NPs adsorption is always lower than that of their uptake.

Recycling waste debris of immobilized microalgae and plant growth-promoting bacteria from wastewater treatment as a resource to improve fertility of eroded desert soil

This study attempted to demonstrate that biological residue from a new biological wastewater treatment is a resource for improving quality of arid soils and plant growth. After tertiary wastewater treatment, debris composed of alginate beads containing the microalgae Chlorella sorokiniana and the plant growth-promoting bacterium Azospirillum brasilense was used as an amendment for eroded, infertile desert soil having low levels of organic matter. A. brasilense survived in these used dried beads for at least one year. Three consecutive applications of the dry debris increased organic matter, organic carbon, and microbial carbon in the soil. Growth of sorghum in the amended soil was greater than plants grown in low organic matter, untreated soil or soil amended with beads containing other combinations of alginate, microalgae, or bacteria. The surface of plant roots growing in the amended soil was heavily colonized by A. brasilense, with no endophytic colonization; root tips were the preferred sites of colonization.

Exploring the interactions between Ca and toxic ions at the cell membrane surface of plant roots in terms of electrical potential at cell membrane surface

Free ion activity of toxic heavy metals has been widely recognized as the most active species for organism, and can be applied for predicting the biological effect of heavy metals. However, the concentration of heavy metal ions at the body surface of organism differs from their free ion activity in the bulk solution, because of cell membrane surface electrical potential ( ψ 0) which varies with solution compositions. An increase in common cation Ca in culture solutions reduces the negativity of ψ 0 by charge screening and ion binding. The reduced negativity could result in reductions in membrane surface activities of cationic toxicants (e.g. Al3+, Cu2+ and Ni2+) and increases in surface activities of anionic toxicants (e.g. SeO42- and H2AsO4-). Therefore, Ca alleviates the toxicity of Al3+, Cu2+ and Ni2+ but increases the toxicity of SeO42- and H2AsO4-. The values of ψ 0 can be calculated with a Gouy-Chapman-Stern model in response to Ca concentrations in solutions. Based on the activity of heavy metal ions at the organism body surface, the biological effect of heavy metals can be well predicted. This study provides a novel avenue into understanding the mechanisms of plant-ion interactions and biological responses of plant.

Phosphorus and Nitrogen Fertilization Effect on Phosphorus Uptake and Phosphatase Activity in Ryegrass and Tall Fescue Grown in a Chilean Andisol

A series of short-term experiments were carried out to assess the effect of phosphorus (P) and nitrogen (ammonium [NH4+-N] or nitrate [NO3−-N]) fertilization on P uptake and phosphatase activity in ryegrass and tall fescue cultivated under greenhouse conditions. Ryegrass or tall fescue plants were grown in an acidic Andisol in the presence or absence of P and increasing doses of NO3−-N or NH4+-N fertilizers. At the end of the experiment, soil phosphatase activity (P-aseRhiz), pH, and Olsen-P were determined in the rhizosphere soil. Plant biomass, P uptake, and root surface phosphatase (P-aseRoot) were also assayed for both plant species. Furthermore, soil incubation experiments at increasing doses of P, NO3−-N, or NH4+-N were performed to evaluate the fertilizer effect on soil phosphatase activity (P-aseBulk) and microbial biomass carbon in the bulk soil. In the absence of plants, P-aseBulk was inhibited and microbial biomass carbon was raised at increasing P supply levels. In the greenhouse experiments, P uptake by tall fescue was about 67% higher than that of ryegrass at low soil P availability, which suggests that tall fescue was less sensitive to P deficiency than ryegrass. For both plant species, P-aseRhiz did not vary as a consequence of P addition. On the other hand, fertilization with the highest NH4+-N dose strongly decreased soil pH and shoot P content, as well as it increased P-aseRoot activity. This fact denotes that P-aseRoot behaved as a strategic response parameter to P stress with insufficient impact on plant P nutrition in both plant species.

A comparative study on the growth and nitrogen and phosphorus uptake characteristics of 15 wetland species

The biomass, root morphology and nutrient uptake capacities of 15 species of local wetland plants were investigated in hydroponic culture. The wetland plants were exposed to 38.5 mg·L−1 of NH-N, 132.8 mg·L−1 of NO-N and 10 mg·L−1 of dissolved inorganic P for 28 days. Mean total biomass of the 15 species ranged from 1.2 to 21.6 g plant−1, with above/below ground ratios (AG:BG) in the range 1.7–5.5. Mean NH-N, NO-N uptake rates ranged from 3.7 to 14.3 mg N·day−1 (accounting for 8.0–49.4% of the NH-N supply) and 17.8 to 59.4 mg N·day−1 (17.8–59.6% of the NO-N supply). Mean P uptake rate ranged from 1.71 to 4.61 mg P·day−1 (24.1–61.5% of the P supply). The N and P concentrations in plant tissues ranged from 28.2 to 606.1 mg N·plant−1 and 4.1 to 53.1 mg P·plant−1, with AG:BG ratio in the range 1.7–7.0 and 1.6–4.6, respectively. The accumulation of N and P in plant tissues was both significantly correlated with plant biomass and root surface area. Among the different species, Canna generalis, Typha latifolia, Thalia dealbata and Lythrum salicaria had greater above- and below-ground biomass, larger root surface area, and greater nutrient uptake and storage rates than the other plants. Our results suggest (or indicate) that the selection of plant species suitable for constructed wetlands can be based on plant biomass and root surface area.

A Comparative Study on the Growth and Nutrient Uptake Characteristics of Fifteen Wetland Species in Taihu Lake Region of China

Fifteen kinds of local wetland plants in Taihu Lake region of China were investigated on their respective growth conditions, biomass allocations and nutrient uptake capacities. The test plants were cultured in 3 L nutrient solutions for 28 days with NH4 +-N, NO3 --N and P concentrations of 38.5, 132.8 and 10 mg/L, respectively. Mean species total biomass ranged from 1.2-21.6 g/plant with above/below ground ratios (AG:BG) between 1.7-5.5. Mean NH4 +-N, NO3 --N and P uptake rates ranged from 3.7-14.3 mg/day (8.0-49.4 % of NH4 +-N supplied), 17.8-59.4 mg/day (17.8-59.6 %) of NO3 --N supplied and 1.71-4.61 mg /day (24.1-61.5 % of P supplied), respectively. Plant tissue N and P concentrations ranged between 28.2-606.1 mg N /plant and 4.1-53.1 mg P/plant, with AG:BG ratio between 1.7-7.0 and 1.6-4.6, respectively. The accumulation of N and P in plant tissues was significantly correlated with plant biomass and root surface area. Among the different species, C. generalis, T. latifolia, T. dealbata and L. salicaria were better than the other plants in above- and below-ground biomass, root surface area, nutrient uptake and storage rates. T. dealbata and L. salicaria were more suitable for year-round application in this area due to their tolerance of coldness.

Efficient colonization of plant roots by the plant growth promoting bacterium Bacillus amyloliquefaciens FZB42, engineered to express green fluorescent protein

A single copy of the gfp gene linked with the P spac promoter and flanked by the terminal FZB42 amyE sequences was stably integrated into the chromosome of plant growth promoting bacterium Bacillus amyloliquefaciens FZB42 via homologous recombination. A spontaneous mutant, FB01mut, emitting bright fluorescence was detected among the transformants and found suitable for colonization experiments performed with Zea mays, Arabidopsis thaliana and Lemna minor. Real-time RT-PCR revealed that FB01mut expressed 2.5 times more of the gfp transcript than the original GFP-labeled strain. Confocal laser scanning microscopy of plant roots infected with gfp+ tagged FZB42 revealed that the bacterium behaves different in colonizing surfaces of plant roots of different species. In contrast to maize, FZB42 colonized preferentially root tips when colonizing Arabidopsis. FZB42 colonized heavily Lemna fronds and roots by forming biofilms consisting of extracellular matrix and cells with altered morphology. Surfactin, but no other lipopeptide or polyketide synthesized by FZB42 under laboratory conditions, was detected in extracts of Lemna plantlets colonized by FZB42. Due to its stable and long-lasting emission of bright fluorescence without antibiotic pressure FB01mut is an excellent tool for studying plant colonization under competitive, environmental conditions.

Natural attenuation of arsenic in the wetland system around abandoned mining area

Mechanisms of natural attenuation of arsenic (As) by wetland plants may be classified by plant uptake and adsorption and/or co-precipitation by iron (oxy)hydroxide formed on the root surface of plants or in rhizosediment. A natural Cattail (Typha spp.) wetland impacted by tailings containing high levels of As from the Myungbong abandoned Au Mine, South Korea was selected, and the practical capability of this wetland to attenuate As was evaluated. The As concentrations in the plant tissues from the study wetland were several-fold higher than those from control wetland. SEM-EDX analyses demonstrated that iron plaques exist on the rhizome surface. Moreover, relatively high As contents bonded with hydrous iron oxides were found in the rhizosediments rather than in the bulk sediments. It was revealed through the leaching and sequential extraction analyses that As existed as more stable forms in the wetland sediment compared with adjacent paddy soil, which is also contaminated with As due to input of mine tailings. The As concentration ratios of extracted solution to sediment/soil represented that the wetland sediment showed significant lower values (10-fold) rather than the paddy soil with indicating high As stability. Also, As in the wetland sediment was predominantly bonded with residual phases on the basis of results from sequential extraction analysis. From these results, it is concluded that transformation of As contaminated agricultural field to wetland environment may be helpful for natural attenuation until active remediation action.

DTAF: an efficient probe to study cyanobacterial-plant interaction using confocal laser scanning microscopy (CLSM)

A variety of microscopic techniques have been utilized to study cyanobacterial associations with plant roots, but confocal laser scanning microscopy (CLSM) is the least used due to the unavailability of a suitable fluorescent dye. Commonly used lectins have problems with their binding ability with root cells and their visualization under CLSM. DTAF (5-(4,6-dichlorotriazinyl) aminofluorescein) is a fluorescent dye that has been widely used for staining various biological samples for fluorescent microscopy. It reacts with polysaccharides and peptides at ordinary conditions. The possible application and efficiency of DTAF for CLSM studies were examined in various aspects of cyanobacterial-plant interactions. Seedlings of Pisum sativum, Vigna rediata and Triticum aestivum were co-cultivated and stained with DTAF as a fluorochrome. Extracellular and intracellular interactions of cyanobacteria and the plant root surface were observed by CLSM. Results were compared with staining by other commonly used lectins. Advantages of the use of DTAF over other stains are its penetration into root tissues and binding with polysaccharides, mainly the cellulose. The staining was smooth, which clearly showed minute details on the cell of surface and root hairs with higher resolution. The emission wavelength for DTAF is 517 nm, which is highly advantageous as cyanobacteria have auto-fluorescence at 665 nm, and both can be simultaneously used in CLSM by visualizing in different channels. This worked efficiently with all three plants used and with filamentous and unicellular cyanobacterial strains. Cyanobacterial presence was not only clearly observed on the root surface, but also inside the root tissue and epidermal cells. The easy protocol and absence of tissue processing make DTAF a useful probe for studies of cyanobacterial associations with plant roots by CLSM.

Cultivation of Phlebopus portentosus in southern China

Phlebopus portentosus is a well-known edible wild mushroom in the tropical part of Yunnan province of China. The mushrooms grow around natural or planted trees of Delonix regia, Mangifera indica, Coffea arabica, Citrus grandis, Artocarpus heterophyllus and Quercus spp. The technology of cultivation of P. portentosus was developed and its biotrophic status examined at Xishuangbanna, Yunnan, China. Uncultivated red soils with and without host plants of C. arabica, C. grandis and M. indica were inoculated with solid inocula of P. portentosus. Matured mushrooms were produced from both inoculated soils, with and without the host plants, 20–30 days after inoculation. No mycorrhizal structures were detected although the fungal mycelia colonized the plant root surfaces. Results show that P. portentosus is a saprobic rather than a symbiotic fungus. Based on this discovery, two methods of cultivation of P. portentosus were developed. Non-sterilized agricultural soils in polypropylene bottles or bags were inoculated with the fungal solid inocula and incubated at a mushroom house. Fruiting-body primordia were produced from the inoculated soils 20–30 days after inoculation. Soil-cased sawdust logs inoculated with P. portentosus produced primordia 10–15 days after casing only. The primordia developed into mature mushrooms 5–6 days later with weights ranging from 20.0 to 135.0 g. The identity of the cultivated fruiting bodies was confirmed by morphological and molecular methods. Our molecular phylogeny based on the Internal Transcribed Spacer sequences from our cultivated isolate and Genbank accessions provides preliminary insight into the phylogeogrpahy of P. portentosus.

Proteomic studies of plant–bacterial interactions

Abstract Plants and bacteria can interact with one another in a variety of different ways. The interaction may be beneficial, harmful or neutral for the plant, and sometimes the impact of a bacterium may vary as the soil conditions change. While a number of different soil bacteria are phytopathogenic, the majority of the more agronomically important plant disease-causing soil microorganisms are fungi. On the other hand, plant growth-promoting bacteria are typically of three general types: those that form a symbiotic relationship with the plant, those that are endophytic and colonize the inner tissues of the plant, and those of soil bacteria, which have competitive abilities to colonize efficiently the rhizosphere and the surface of plant roots. While there have been significant advances in elucidating the mechanistic details of plant–bacterial interactions in recent years, many fundamental questions about these processes remain. Unfortunately, studies that focus on only a single biochemical pathway or mechanism often miss the multiplicity of effects that plants and bacteria have on one another, motivating the employment of broader proteome-wide approaches. On the other hand, using proteomics technology including high-resolution two-dimensional gel electrophoresis (2-DE) and high-sensitivity mass spectrometry (MS), it is possible to gain greater insight into the detailed impact that plants and soil bacteria have on one another. In this regard, of all of the proteomic studies of plant–bacterial interactions, the symbiotic interaction between nitrogen-fixing bacteria and legumes has been studied in the greatest detail. Studies of the proteome of plant–pathogen interactions have also received considerable attention. However, there are currently very few proteomic studies of endophytic and rhizosphere associated plant growth promoting bacteria. Here, some fundamental proteomic tools are introduced and the applications of one of these approaches (i.e., 2-DE coupled to MS) to the study of plant–bacterial interactions are discussed. This review specifically addresses the questions: what are the impacts of plants on the bacterial proteomes, and vice versa?

Establishment of an Inoculated Bacterial Strain on Plant Root Surfaces in Soils with Different Microbial Community

Soil microbial community changed due to the application of a biological fertilizer EM-Bokashi™ and microwave radiation. Root colonization of sugar beet by Pseudomonas fluorescens DR54 was enhanced in sterilized soil but not in soils amended with EM-Bokashi. Therefore, EM-Bokashi can be a potential means to alter soil microbial diversity and soil sterilization can be a practical means to enhance plant root colonization by microbial inoculants under controlled conditions such as nursery and greenhouse crops.

English

The purpose of in situ or in-place treatment of metal mine wastes is to immobilize contaminants within the soil/plant complex, reduce metal and arsenic movement to groundwater, reduce metal and arsenic movement to receiving streams, stabilize the landscape from wind erosion, and to provide a functional ecosystem compatible with current and future land uses. In-place treatment includes the incorporation of chemical and biological amendments to provide a hospitable rootzone, and to select plant species that can thrive in the newly amended environment. During in-place treatment, metals are chemically precipitated, and/or sequestered by complexation and sorption mechanisms within the mine wastes/ contaminated soils. Metal availability to plants is minimized, and metal leaching into groundwater is reduced. Metals and arsenic that remain in soil solution are immobilized via chemical reactions at plant root surfaces. The selection of plant species for in-place treatment is based on availability of seed or seedlings, the species' relative lack of ability to translocate (or move) metals and arsenic from the roots into the above ground biomass of the plant, and land use and management considerations. In-place treatment does not remove contaminants from the soil. As a consequence, short-term and long-term effectiveness of in-place treatment has been and continues to be debated. One concern is the potential toxicity to livestock and wildlife from the contaminants in soils and/or plants. This paper provides vegetation metal data from several Superfund and AML sites at which in-place treatment has been used as a remedial strategy. Interpretations of these data based on plant toxicity and residual risk to terrestrial receptors including grazing animals are presented.

Rhizobium etli HrpW is a pectin-degrading enzyme and differs from phytopathogenic homologues in enzymically crucial tryptophan and glycine residues

While establishing a nitrogen-fixing symbiosis with leguminous plants, rhizobia are faced with the problem of penetrating the plant cell wall at several stages of the infection process. One of the major components of this barrier is pectin, a heteropolysaccharide composed mainly of galacturonic acid subunits. So far, no enzymes capable of degrading pectin have been isolated from rhizobia. Here, we make an inventory of rhizobial candidate pectinolytic enzymes based on available genome sequence data and present an initial biochemical and functional characterization of a protein selected from this list. Rhizobium etli hrpW is associated with genes encoding a type III secretion system, a macromolecular structure that allows bacteria to directly inject so-called effector proteins into a eukaryotic host's cell cytosol and an essential virulence determinant of many Gram-negative pathogenic bacteria. In contrast to harpin HrpW from phytopathogens, R. etli HrpW possesses pectate lyase activity and is most active on highly methylated substrates. Through comparative sequence analysis, three amino acid residues crucial for the observed enzymic activity were identified: Trp192, Gly212 and Gly213. Their importance was confirmed by site-directed mutagenesis and biochemical characterization of the resulting proteins, with the tryptophan mutant showing no detectable pectate lyase activity and the double-glycine mutant's activity reduced by about 80 %. Surprisingly, despite hrpW expression being induced specifically on the plant root surface, a knockout mutation of the gene does not appear to affect symbiosis with the common bean Phaseolus vulgaris.

Aflatoxins Effect on Fungal Populations of Soil, Root and Leaf Surface of Peanut Plants in the Field with Special Reference to Aflatoxins Biodegradation

Aflatoxins Effect on Fungal Populations of Soil, Root and Leaf Surface of Peanut Plants in the Field with Special Reference to Aflatoxins Biodegradation

Microbial community responses associated with the development of Fusarium oxysporum f. sp. cucumerinum after 24-epibrassinolide applications to shoots and roots in cucumber

Fusarium wilt, caused by Fusarium oxysporum f. sp. cucumerinum (FO), is one of the major diseases in cucumber (Cucumis sativus) production. Root and foliar applications of 24-epibrassinolide (EBL), an immobile phytohormone with antistress activity, were evaluated for their effects on the incidence of Fusarium wilt and changes in the microbial population and community in roots of cucumber plants. EBL pre-treatment to either roots or shoots significantly reduced disease severity followed by an improved plant growth regardless of the treatment methods applied. EBL applications decreased the Fusarium population on root surfaces and in nutrient solution, but increased the population of fungi and actinobacteria on root surfaces. PCR-DGGE analysis showed that FO-inoculation had significant effects on the bacterial community on root surfaces as expressed by a decreased diversity index and evenness index, but EBL applications alleviated these changes. Moreover, several kinds of decomposing bacteria and growth-promoting bacteria were identified from root surfaces of FO-inoculated plants and EBL-pre-treated plants, respectively. Overall, these results show that the microbial community on root surfaces was affected by a complex interaction between phytohormone-induced resistance and plant pathogens.

Influence of Chelating Ligands on Arsenic Uptake by Hydroponically Grown Rice Seedlings (Oryza sativa L.): A Preliminary Study

AbstractFerric (oxyhydro‐)oxides (FeOx) precipitate in the rhizosphere at neutral or alkaline pH and are adsorbed on the plant root surfaces. Consequently, the higher binding affinity of arsenate to FeOx and the low iron phytoavailability of the precipitated FeOx make the phytoremediation of arsenic difficult. In the present study, the influence of chelating ligands on arsenic and iron uptake by hydroponically grown rice seedlings (Oryza sativa L.) was investigated. When chelating ligands were not treated to the growth medium, about 63 and 71% of the total arsenic and iron were distributed in the root extract (outer root surfaces) of rice, respectively. On the other hand, ethylenediaminetetraacetic acid (EDTA), ethylenediaminedisuccinic acid (EDDS) and hydroxyiminodisuccinic acid (HIDS) desorbed a significant amount of arsenic from FeOx of the outer root surfaces. Therefore, the uptake of arsenic and iron into the roots and their subsequent translocation to the shoots of the rice seedlings increased significantly. The order of increasing arsenic uptake by chelating ligands was HIDS > EDTA > EDDS. Methylglycinediacetic acid (MGDA) and iminodisuccinic acid (IDS) might not be effective in arsenic solubilization from FeOx. The results suggest that EDDS and HIDS would be a good and environmentally safe choice to accelerate arsenic phytoavailability in the phytoremediation process because of their biodegradability and would be a competent alternative to the widely used non‐biodegradable and environmentally persistent EDTA.

A novel method for sampling bacteria on plant root and soil surfaces at the microhabitat scale

This study reports the first method for sampling bacteria at a spatial scale approximating a microhabitat. At the core of this method is the use of tungsten rods with laser-cut tips of known surface area (0.013 mm 2). Exposed plant root or soil surfaces were viewed with a dissecting microscope and micro-sampling rods were guided to sample sites using a micro-manipulator. Bacteria that adhered to the sampling tips were then recovered for microbiological analyses. The efficiency of this method for removing bacteria from root surfaces was similar to that with which bacteria are recovered from dissected root segments using the conventional technique of washing. However, as the surface area of the micro-sampling tips was known, the new method has the advantage of eliminating inaccuracy in estimates of bacterial densities due to inaccurate estimation of the root or soil surface sampled. When used to investigate spatial distributions of rhizoplane bacteria, the new technique revealed trends that were consistent with those reported with existing methods, while providing access to additional information about community structure at a much smaller spatial scale. The spatial scale of this new method is ca. 1000-times smaller than other sampling methods involving swabbing. This novel technique represents an important methodological step facilitating microbial ecological investigations at a microhabitat scale.

Colonization pattern of plant root and leaf surfaces visualized by use of green-fluorescent-marked strain of Methylobacterium suomiense and its persistence in rhizosphere

The localization of bacterial cell, pattern of colonization, and survival of Methylobacterium suomiense CBMB120 in the rhizosphere of rice and tomato plants were followed by confocal laser scanning, scanning electron microscopy, and selective plating. M. suomiense CBMB120 was tagged with green fluorescent protein (gfp), and inoculation was carried out through seed source. The results clearly showed that the gfp marker is stably inherited and is expressed in planta allowing for easy visualization of M. suomiense CBMB120. The colonization differed in rice and tomato -- intercellular colonization of surface-sterilized root sections was visible in tomato but not in rice. In both rice and tomato, the cells were visible in the substomatal chambers of leaves. Furthermore, the strain was able to compete with the indigenous microorganisms and persist in the rhizosphere of tomato and rice, assessed through dilution plating on selective media. The detailed ultra-structural study on the rhizosphere colonization by Methylobacterium put forth conclusively that M. suomiense CBMB120 colonize the roots and leaf surfaces of the plants studied and is transmitted to the aerial plant parts from the seed source.

Sequence-based analysis of pQBR103; a representative of a unique, transfer-proficient mega plasmid resident in the microbial community of sugar beet.

The plasmid pQBR103 was found within Pseudomonas populations colonizing the leaf and root surfaces of sugar beet plants growing at Wytham, Oxfordshire, UK. At 425 kb it is the largest self-transmissible plasmid yet sequenced from the phytosphere. It is known to enhance the competitive fitness of its host, and parts of the plasmid are known to be actively transcribed in the plant environment. Analysis of the complete sequence of this plasmid predicts a coding sequence (CDS)-rich genome containing 478 CDSs and an exceptional degree of genetic novelty; 80% of predicted coding sequences cannot be ascribed a function and 60% are orphans. Of those to which function could be assigned, 40% bore greatest similarity to sequences from Pseudomonas spp, and the majority of the remainder showed similarity to other gamma-proteobacterial genera and plasmids. pQBR103 has identifiable regions presumed responsible for replication and partitioning, but despite being tra+ lacks the full complement of any previously described conjugal transfer functions. The DNA sequence provided few insights into the functional significance of plant-induced transcriptional regions, but suggests that 14% of CDSs may be expressed (11 CDSs with functional annotation and 54 without), further highlighting the ecological importance of these novel CDSs. Comparative analysis indicates that pQBR103 shares significant regions of sequence with other plasmids isolated from sugar beet plants grown at the same geographic location. These plasmid sequences indicate there is more novelty in the mobile DNA pool accessible to phytosphere pseudomonas than is currently appreciated or understood.