Root Junction Research Articles

Transcriptome mechanisms of dandelion under stress of polystyrene and dibutyl phthalate and quantitative tracing of nanoplastics

Polystyrene nanoplastics (PS NPs) and dibutyl phthalate (DBP) pollution pose significant risks to ecosystems and contribute to bioaccumulation in plants, yet uptake mechanisms and combined toxicity are poorly understood. We used fluorescent labeling and europium-doped PS NPs to reveal the absorption and translocation of NPs by dandelions and conducted a transcriptomic analysis under PS NPs and DBP exposure. The results indicated that NPs are transported horizontally through the intercellular gaps at the root tips and primary root-lateral root junctions via the apoplastic pathway, followed by longitudinal transport through the xylem vessels under the transpiration stream. Co-exposure significantly reduced the bioconcentration factors of dandelion seedlings by 113 % but increased the NP transfer factors by 33.8 %. Transcriptomic analysis confirmed that exposure to PS NPs and DBP activated gene expression in dandelion shoots and roots. The differentially expressed genes were primarily involved in the photosynthesis, plant hormone signal transduction, and phenylpropanoid biosynthesis pathways. Weighted gene co-expression network analysis identified key genes and hub transcription factors playing crucial roles in regulating dandelion's response to combined stress. Our study provides new insights into the plant toxicity mechanism underlying the interaction between PS NPs and DBP, highlighting the adverse effects of the combined pollution on plant health.

Comparative evaluation of two different dental age estimation methods using tooth pulp: A CBCT study.

To estimate the age of an individual based on 3D radiographic evaluation of pulp width of maxillary central incisor. This study included 185 CBCT images of individuals within age range of 14-64 years. Images were evaluated for maxillary central incisors and pulp width measurements were taken from cementoenamel junction and middle third of root. Obtained data was subjected to correlation and regression analysis from which the age of an individual was predicted. Results of the present study were compared with another study by the same authors. A negative linear relationship was obtained between age and pulp width. The standard error of estimate (SEE) in sagittal section was 11.36 years and that in coronal section was 11.23 years. The coefficient of determination for sagittal section was 0.107 and for coronal section was 0.127. An obtained regression formula was highly significant. Division of samples into various age groups reduced SEE drastically. It can be concluded that pulp width of maxillary central incisor is a reliable indicator of age estimation.

Histological alterations in chilli pepper (Capsicum annuum L.) roots associated with sudden wilt syndrome

AbstractSudden wilt syndrome of chilli, an emerging and destructive disorder, is characterized by an abrupt appearance that has increased in Indo‐Gangetic alluvial plains over the past decade. The primary cause associated with the problem is water stagnation that creates hypoxic conditions in the root zone, and the plant mortality is further aggravated by soil‐borne fungi Fusarium oxysporum. The effects of sudden wilt on chilli roots were studied morphologically and histologically, using root scanning, optical microscopy and electron microscopy. Significant changes with respect to root length, projected area, number of root tips and root segments, average root diameter as well as estimated volume of roots were observed via root scanning of healthy and diseased root samples. Through optical microscopy of sections of the microtome‐cut root junctions displayed normal epidermis in healthy plants, while swollen cells indicated stress in the diseased plants. Cells of laterals and root tips in healthy plants were intact and stained strongly, but because of damaged tissues, cells in diseased plants were macerated and stained weakly. Root tips of healthy plants contained mitotic zones, whereas diseased root tips lacked mitotic zones. Electron microscopy studies revealed that sudden wilt had an adverse impact on xylem diameter, stele diameter, epidermal thickness and cortex thickness as evidenced by significantly lesser values of these parameters. The present study is the first systematic attempt to examine the morphological, histological and ultrastructural changes in chilli in response to sudden wilt syndrome.

Evaporation-driven internal hydraulic redistribution alleviates root drought stress: Mechanisms and modeling.

Many tree species have developed extensive root systems that allow them to survive in arid environments by obtaining water from a large soil volume. These root systems can transport and redistribute soil water during drought by hydraulic redistribution (HR). A recent study revealed the phenomenon of evaporation-driven hydraulic redistribution (EDHR), which is driven by evaporative demand (transpiration). In this study, we confirmed the occurrence of EDHR in Chinese white poplar (Populus tomentosa) through root sap flow measurements. We utilized microcomputed tomography technology to reconstruct the xylem network of woody lateral roots and proposed conceptual models to verify EDHR from a physical perspective. Our results indicated that EDHR is driven by the internal water potential gradient within the plant xylem network, which requires 3 conditions: high evaporative demand, soil water potential gradient, and special xylem structure of the root junction. The simulations demonstrated that during periods of extreme drought, EDHR could replenish water to dry roots and improve root water potential up to 38.9% to 41.6%. This highlights the crucial eco-physiological importance of EDHR in drought tolerance. Our proposed models provide insights into the complex structure of root junctions and their impact on water movement, thus enhancing our understanding of the relationship between xylem structure and plant hydraulics.

Insight into the absorption and migration of polystyrene nanoplastics in Eichhornia crassipes and related photosynthetic responses

Nanoplastics, as emerging contaminants are being released into aquatic environments with their increasing applications, and induce potential hazards to aquatic ecosystem. In this work, we investigated the removal process of polystyrene nanoparticles (PS NPs) by Eichhornia crassipes and the related photosynthetic responses of E. crassipes. Results showed that both sizes of PS NPs (20 and 200 nm) with 50 mg/L induced the prominent damage on the root epidermis after 48 h exposure, and smaller size PS NPs caused the greater damage. PS NPs has been entered the roots of E. crassipes and migrated from the epidermis, cortex, to vascular system by using confocal laser scanning microscopy observation. Scanning electron microscope images confirmed the distribution of PS NPs (200 nm) in the roots. The crack at sites of primary-lateral root junction was an important way for the uptake of PS NPs, which destroyed the defense of Casparian strip, and promoted the migration of PS NPs into the vascular system. PS NPs entered the submerged leaves by stomata and the intercellular spaces of lower epidermis. Moreover, PS NPs in the plants showed significant inhibition on net photosynthetic rate, intercellular CO2 concentration, stomatal conductance, and transpiration rate. This study concluded the absorption and migration processes of PS NPs by E. crassipes, and the negative effects on photosynthesis, which will be useful for guiding the floating plants application for PS NPs removal in aqueous environment and ecological improvement.

Differential Colonization of the Plant Vasculature Between Endophytic Versus Pathogenic Fusarium oxysporum Strains.

Plant xylem colonization is the hallmark of vascular wilt diseases caused by phytopathogens within the Fusarium oxysporum species complex. Recently, xylem colonization has also been reported among endophytic F. oxysporum strains, resulting in some uncertainty. This study compares xylem colonization processes by pathogenic versus endophytic strains in Arabidopsis thaliana and Solanum lycopersicum, using Arabidopsis pathogen Fo5176, tomato pathogen Fol4287, and the endophyte Fo47, which can colonize both plant hosts. We observed that all strains were able to advance from epidermis to endodermis within 3 days postinoculation (dpi) and reached the root xylem at 4 dpi. However, this shared progression was restricted to lateral roots and the elongation zone of the primary root. Only pathogens reached the xylem above the primary-root maturation zone (PMZ). Related to the distinct colonization patterns, we also observed stronger induction of callose at the PMZ and lignin deposition at primary-lateral root junctions by the endophyte in both plants. This observation was further supported by stronger induction of Arabidopsis genes involved in callose and lignin biosynthesis during the endophytic colonization (Fo47) compared with the pathogenic interaction (Fo5176). Moreover, both pathogens encode more plant cell wall-degrading enzymes than the endophyte Fo47. Therefore, observed differences in callose and lignin deposition could be the combination of host production and the subsequent fungal degradation. In summary, this study demonstrates spatial differences between endophytic and pathogenic colonization, strongly suggesting that further investigations of molecular arm-races are needed to understand how plants differentiate friend from foe. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Structure and dynamics of a laminar separation bubble near a wing root: towards reconstructing the complete LSB topology on a finite wing

The influence of the wing root junction on the laminar separation bubble forming on the suction surface of a semispan NACA 0018 wing cantilevered from the wind tunnel test section wall is studied using surface flow visualisations, particle image velocimetry and surface pressure measurements at a chord Reynolds number of 125 000 and an angle of attack of 6 $^\circ$ . The test section wall boundary layer upstream of the wing is turbulent, and the spanwise influence of the junction on the separation bubble extends well beyond the test section wall boundary layer thickness. Substantial three-dimensionality is seen in the separation bubble flowfield near the wing root, where earlier transition and a reduction in separation bubble thickness is observed. In contrast with the wing tip, earlier transition and a reduction in separation bubble length occurs near the wing root. Outside of the junction affected region, the separation bubble is similar to separation bubbles forming on two-dimensional geometries, and displays mild spanwise waviness. The transition process away from the end affected regions is characterised by the formation of spanwise roll-up vortices that are shed in a nearly two-dimensional manner across the span. The analysis of the results shows that, near the wing root, the increased level of perturbations leads to earlier vortex roll-up and spanwise flow contributes to more rapid vortex breakdown. The results in the wing root region are complemented by the analysis of data from Toppings and Yarusevych (J. Fluid Mech., vol. 929, 2021, A39) in the wing tip region to provide a more holistic outlook on the laminar separation bubble topology and dynamics on the entire finite wing.

Mechanical Characteristics of Variable Cross‐Section Immersed Tunnels under Spatial Differential Settlement

This work establishes a fine model reflecting the characteristics of immersed tube structures to study the spatial mechanical characteristics of variable cross section immersed tunnels. Then, the mechanical behavior of the pipe segments under differential deformation is explored, based on which we propose a formula for estimating the shear key force and analyze the corresponding failure mechanism and failure mode. Thus, the critical points of the pipe segment design are specified. The results show that, first, the variable cross section segment bears more sectional internal force (over 47%) than the uniform cross section segment in actual cases, which should be fully considered in practical reinforcement design. Bearing deformation alternatively occurs at different shear keys, implying an apparent spatial stiffness matching problem. Second, the pipe segments show overall settlement under longitudinal bending, failing to satisfy the assumption of deformed plane sections. The force on the shear keys varies with the quadratic function of the longitudinal bending degree, and the dislocation magnitude has a positive near‐linear relationship with the bending degree. Third, when subjected to torsion, the shear keys of the weak sidewalls are sheared to resist torsion. Then, this force is laterally transferred to the top and bottom plates and jointly shared by the adjacent shear keys, explaining why shear is adjusted with structural deformation. Fourth, under the action of spatial differential deformation, the shear force is mainly undertaken by the vertical shear keys. When the structure is subjected to bending, compression and shear failure occur at the end angle of the middle wall shear key, and its root junction experiences tension and shear failure. When subjected to longitudinal torsion, the local tension and shear failure at the root of the shear key on the soft subgrade side cause a joint failure. Finally, based on the bearing characteristics, failure mechanism, and failure mode of variable cross section immersed tunnels, the idea of strengthening immersed tube structures is put forward, which can guide similar engineers.

A small cog in a large wheel: crucial role of miRNAs in root apical meristem patterning.

In both animal and plants, establishment of body axes is fundamental for proper organ development. Plant roots show two main developmental axes: the proximo-distal axis, which spans from the hypocotyl-root junction to the root tip; and the radial axis, which traverses from the vascular tissue to the epidermis. Root axes are determined in the root meristem. The root meristem occupies the tip of the root and contains self-renewing stem cells, which continuously produce new root cells. An intricate network of signalling pathways regulates meristem function and patterning to ensure proper root development and growth. In the last decade, miRNAs, 20-21 nucleotide-long molecules with morphogenetic activity, emerged as central regulators of root cell patterning. Their activity intersects with master regulators of meristematic activity, including phytohormones. In this review, we discuss the latest findings about the activity of miRNAs and their interaction with other molecular networks in the formation of root meristem axes. Furthermore, we describe how these small molecules allow root growth to adapt to changes in the environment, while maintaining the correct patterning.

Dental health indicators of the Chernyakhov population from Shyshaki (Ukraine)

Odontological studies of ancient populations represent different indicators related to health state, lifestyle and human diet. The aim of this paper is to determine the dental health indicators in the Chernyakhov population (the end of the IVth c. AD) from Ukraine. The paper also attempts to identify the relationship between sex and these indicators in the studied population. The sample analysed consisted of the dental remains of 25 adult individuals (11 males and 14 females) and 8 children individuals excavated from the cemetery at the archaeological site of Shyshaki (Poltava region of Ukraine). A total of 760 teeth were examined for caries, tooth wear and calculus clinically, and 647 teeth of adults were observed radiographically. The studied population presents frequency of caries in individuals of 12.5%. This indicator in adult male and female dentition is 42.86% and 14.0% respectively, and 25% in children. The presented population frequency of caries teeth was 0.88%. Females presented higher caries rate than males (2.72 % females vs. 0.36 % males) (p<0.05). The most frequent were caries lesions of cementum-enamel junction (40%) and combined lesions of crown and root (40%) with no difference in terms of sex. Frequency of dental wear in adult individuals and 8-10 year-old individuals was 100%. The studied population represented TWI (tooth wear index) in adults (2.26), which increased with aging, but the difference in terms of sex is insignificant. Calculus was observed in 64.28% of the females and 63.33% of the males, showing no statistical difference (p>0.5). These findings confirm a very low rate of caries teeth in the territory of Shyshaki during the Late Roman period, which could be related to regional diet and concentration of fluorine in drinking water. The Chernyakhov population presents high dental wear and similar frequency of dental calculus when compared to the population from Roman Britain. Females presented significantly higher frequency of caries than males, whereas no significant sex differences were found regarding dental wear, calculus, and localisation of caries lesions. The authors presume that dental health indicators in the Chernyakhov culture need to be studied more with bigger sample size and data of the populations from other regions of Ukraine.

Acoustic Methods for Testing Gas Turbine Engine Blades

In this paper the application technology of the ultrasonic testing method in the process of the PS-90A aircraft engine manufacturing is considered. It is known that the development and implementation of monocrystalline turbine blades for aircraft gas turbine engines are aimed at ensuring the material effectiveness or increasing the blade service life in comparison with polycrystalline blades. It is achieved at the cost of the increased long-term material strength in the same temperature range. Based on the results of the process and metallographic studies analysis, it has been established that during the structure formation under the internal stress action, hot crystallization cracks with an opening from 3 to 8 μm or more and a length of 3 to 35 mm along the grain boundaries can appear. Grains formation in most blades happens with their subsequent exit to the lock end, a bridge. The formation of hot cracks most likely occurs at a large grain disorientation angle (more than 25°). Grain boundaries on blades with hot crystallization cracks are located, as a rule, on the bridge at the junction of the blade root with the blade shank (“bottleneck”) with orientation along the blade axis. The method of contact laser-ultrasonic flaw detection (CLUFD) was tested on blades in the region of bridges using both pilot samples and standard parts in order to solve an urgent production and technical problem, that is timely detection of hot crystallization cracks in rotating turbine engine blades at the manufacturing stage. The use of the phased antenna array technology (PAR) in combination with a portable X-32 flaw detector represents a new level of blade ultrasonic testing. The flaw detector operates in a wide frequency range, which allows solving a very large range of various ultrasonic testing problems. The advantages and possibilities of the PAR technology with the portable X-32 flaw detector can be considered on the example of the turbine blade lock testing. S-scan (sector-scan) makes it possible to interpret the received signals quickly and easily.

Phonological Interpretation of Consonants in the Russian Language in Borrowings at the Junction of Prefix and Root

The article is devoted to the phonological interpretation of consonants at the junction of prefix and root in borrowings such as Russian ir-ratsionalnyy, ir-realnyy, in-novatsiya, im-moralnyy, etc. The work is performed taking into account the typology of long and short consonant opposition in different languages of the world. The broad phonological context of the use of long and short consonants in the Russian language is taken into account, but due to the limited volume of the article, illustrations and interpretations of a number of phenomena are given in a generalized form. The author proceeds from the concept of multilevel phonology, developed by him in a number of works. In general, the description is based on primary phonemes that correspond to the phonemes of the Saint Petersburg Phonological School. It is shown that when identifying the morphemic structure of words such as irratsionalnyy one should proceed not from the spelling appearance, but from the accepted pronunciation. With this approach, the morphemic division of the previously cited words takes the following form: i-rationalnyy, i-realnyy, i-novatsiya, i-moralnyy, etc. Thus, the article deals with the problem of creating a phonological description in the conditions of orthoepic uncertainty and variability using a specific example.

Patent Ductus Arteriosus: Update Review

The Ductus Arteriosus (DA) is a vascular structure of the fetal heart that communicates the isthmus of the aorta (at the junction of the aortic root with the descending aorta) to the roof of the bifurcation of the pulmonary trunk. It is an essential structure of the fetal heart that connects the pulmonary circulation to de systemic circulation bypassing the lungs. The DA is usually patent at birth. It undergoes through muscle contraction between 10 and 15 hours of life and closes due to fibrous proliferation of the intimal layer by the third week of life. The change in the natural history of DA, with consequent permeability beyond the predicted period, promotes the Patent Ductus Arteriosus (PDA) a congenital acyanotic heart disease. The most important risk factor for PDA is prematurity. Other risk factors are the congenital rubella, chromosomal abnormalities, genetic factors, low birth weight, perinatal asphyxia and birth in high altitude places. The clinical manifestations of a PDA are determined by the degree of left-to-right shunting, which is dependent upon age, the size and length of the PDA and the difference between pulmonary and systemic vascular resistances. The diagnosis of PDA is usually based on its characteristic clinical findings and confirmation by echocardiography. The proper management of PDA depend on age, hemodynamic impact and resource available and may include conservative management, pharmacologic treatment, surgical approach and percutaneous closure. The complication rates for percutaneous and surgical closure are rare.

Colonization on Cotton Plants with a GFP Labeled Strain of Bacillus axarquiensis.

Verticillium dahliae was one of the most important diseases caused Verticilliumwiltofcotton. In our previous study, Bacillus axarquiensis TUBP1 was screened and found to be an antagonistic strain against V. dahliae with 43% biocontrol effect in the cotton field. In order to uncover the functional mechanism of B. axarquiensis against Verticillium wilt in cotton, the colonization of B. axarquiensis labeled with a green fluorescent protein (GFP) was investigated in cotton plants and the rhizosphere soil. Firstly, a plasmid (pHT-315) containing gfp gene was successfully transformed into wild B. axarquiensis TUBP1 and labeled a green fluorescence by electroporation, which didn't change the bioactivity in vitro. In gnotobiotic conditions, cotton seeds were then inoculated with the gfp-labeled strain and grown in green house. Observation with a confocal laser scanning microscope and a scanning electron microscope showed that GFP-labeled B. axarquiensis TUBP1 infected cotton roots and widely distributed in epidermis, cortical parenchyma, intercellular spaces, the xylem vessels, and pith cells as well as root hair cells through cracks formed at the lateral root junctions, followed by a slow migration from roots to stems and leaves. Quantitative fluorescence and flow cytometry (FACS) approaches showed a gradual decrease in the number of TUBP1-315gfp with increasing inoculation time. However, TUBP1-315gfp levels were detectable till 45days after planting. In contrast, no fluorescence signal was detected in the non-inoculated groups. Therefore, GFP-labeled B. axarquiensis TUBP1 exhibited colonization in different parts of cotton plants from the rhizosphere soil.

Vessel elements of two thelypteroid ferns-part I

BackgroundHydraulically efficient xylem was evolved in the vascular plants as an apomorphy of the group. Main xylem components involved in water conduction are tracheid and vessel. Vessels, in which two ends are perforated, constituted major evolutionary innovation within vascular plants, presumably providing more efficient solute conduction. Not all vascular plants have vessels. In pteridophytes vessels are present only in seven genera. The contention lies regarding the presence and distribution of vessel in pteridophytes are the impulsive force of this investigation.MethodsTracheary elements are isolated following the standard maceration technique, then hand-razor cut longisections are passed through the aqueous alcohol grades and air-dried samples are placed on stub, sputter coated with gold and examined with SEM.ResultsTwo thelypteroid ferns viz. Ampelopteris prolifera (Retz.) Copel. and Thelypteris interrupta (Willd.) K. Iwats. are having vessel elements in root, rhizome, stipe, rachis, primary vein/costa, root-rhizome and rhizome-petiole junction i.e. through entire vascular connection of the plant body though the vessel network is interrupted and joined with parenchyma at the end in some places. Presence of vessel elements in the costa of pteridophytic taxa is first time reported by this study. Vessel end-walls are obliquely placed (root, rhizome, and stipe) but oblique to horizontal orientation is noticed in the primary vein/costa. End-walls are with simple, intermediate and compound perforation plates observed through SEM imaging as well as with tissue specific stain. Studied taxa are grown either in terrestrial microclimate of two contrasting environments i.e. sun and shade (A. prolifera) or in open swampy land (T. interrupta) with moderate to highly disturbed places as rapid proliferating populations showing interpopulation variations of tracheary elements length–width(s) and vessel end-wall length–width(s).ConclusionVessel elements are present throughout the entire vascular connections of the plant body of A. prolifera (Retz.) Copel. and T. interrupta (Willd.) K. Iwats. Interpopulation variation of tracheary elements length–width(s) and vessel end-wall length width(s) are noticed. Till date only seven genera of pteridophytes are reported for the presence of vessel and these two genera are the new addition with the previous.

The predictive value of the epicardial adipose thickness in the rate of expansion of the aortic root.

Epicardial adipose tissue (ECAT) is metabolically active and is involved in the development of atherosclerosis. The thickness of ECAT has been positively correlated with the dimensions of the ascending aorta. We aimed to examine whether ECAT thickness predicted the expansion of the aortic dimensions. The imaging results of patients who had undergone transthoracic echocardiographic (TTE) examinations more than twice during the period 2005-2015 were surveyed. We included adult patients who had undergone TTE examinations at least 1year apart. The ECAT was measured in the parasternal long-axis view from the index TTE study. End-diastolic dimensions in three consecutive beats were averaged for all measurements. The annulus, root, and sinotubular junction (STJ) were also measured. The amount of increase (if any) in aortic dimensions per year was calculated and the correlation of this increase with the initial thickness of the ECAT was analyzed. In total, 429 examinations were performed with 197 patients (17females), from which 394 examinations were analyzed. The ECAT thickness was 8.6 ± 3.6 mm. In the initial examinations, the annulus, STJ, and root measured 23 ± 4, 28 ± 4, and 34 ± 4 mm, respectively. In univariate analysis, for every 1 mm of ECAT thickness, the STJ expanded 0.056 (95% CI: 0.001-0.112 mm/year; p = 0.030) and the aortic root expanded 0.088 mm/year (p < 0.001). In multivariate analysis, ECAT thickness remained an independent predictor of the aortic root expansion. For every 1‑mm increase in ECAT thickness, the aortic root expanded by 0.036 mm (95% CI: 0.010-0.062) per year (p = 0.007). The thickness of the ECAT is apredictor of more rapid increases in the dimensions of the aortic root. Further studies of patients with established aortic aneurysm are warranted.

Visualising confirmation of the endophytic relationship of Metarhizium anisopliae with maize roots using molecular tools and fluorescent labelling

ABSTRACTMetarhizium anisopliae, an entomopathogenic fungus, is found to contribute to plant nutrient uptake and condidered as a plant endophyte. However, there is very little visual evidence that demonstratrates the endophytic relationship. Since the incidence of Metarhizium within host plants may be ephemeral or of limited distribution within host tissue, visualisation is reliant on both presence and the ability to detect the fungus even when present at low levels. We inoculated maize seeds with an egfp-labelled isolate of M. anisopliae, and then detected the egfp fragment by qualitative and quantitative PCR, and examined fluorescence of mycelia in the inoculated roots by laser scanning confocal microscopy (LSCM). The optimised PCR qualitatively identified the presence of egfp-labelled M. anisopliae at a 1:3000 M. anisopliae-maize DNA ratio. Root samplings of inoculated plants at intervals over 24 days were discovered egfp-labelled fragments with 14-d roots having the highest proportion with amplification. The egfp-label concentrations ranged very low in 2.976 × 10−7.42∼−7.02 ng/μL, with a rise process in 4–11 days after M. anisopliae treatment. Under LSCM, fluorescent mycelia in roots were identified, and the clear images were captured to show hyphal development extending along a longitudinal line of root cells and even forming a hyphal mass in the intercellular space. There were many hyphae at the branch junctions of the lateral roots. The methodology used to detect the fungus will be important for exploring the multi-trophic function of M. anisopliae and co-evolution in plants.

Application of rice (Oryza sativa L.) root endophytic diazotrophic Azotobacter sp. strain Avi2 (MCC 3432) can increase rice yield under green house and field condition

Use of plant-associated beneficial microbes, especially endophytes are getting popular day by day as they occupy a relatively privileged niche inside different plant tissues with lesser competition for food and shelter than rhizosphere. The effects of different physical factors like temperature, rainfall, and seasonal variation and UV radiation on plant growth promoting endophytic communities are less pronounced than those on the rhizospheric and phylloplane microbes. This present work has been compromised with further utilization of an indigenous rice (Oryza sativa L.) root endophytic Azotobacter sp. strain Avi2 (MCC 3432) (AzA) as a bio-formulation for sustainable rice production based on several physiological parameters (plant height, root length/weight, leaf area, yield, chlorophyll contain), in-vitro comparative plant growth promoting assays, greenhouse and field experiments (dry and wet season). Treatments with AzA exhibited higher yield as well as maximal chlorophyll fluorescence (Fm) of flag leaves in flowering and grain filling stages indicating higher photosynthetic rates. Scanning electron microscopic image of rice roots demonstrated accumulation of bacterial biofilm at the junction of primary and lateral root confirming the root-colonizing ability of the bacterium. The results of the study were quite encouraging as AzA exhibited better vegetative and reproductive growth of rice in pot and field experiment compared to formulated rhizospheric Azotobacter sp. (commercial product). Apart from that plants treated with AzA (supplemented 50% nitrogenous fertilizer of recommended dose) exhibited similar yield parameters when it was compared with the recommended dose of fertilizer (RDF; 120:60:60 mg N:P:K kg−1 soil/ without any bacterial). Therefore, it can be concluded that application of this plant growth promoting endophyte can reduce a substantial amount of N-fertilizer for field application.

Isolation, characterization, genomic sequencing, and GFP-marked insertional mutagenesis of a high-performance nitrogen-fixing bacterium, Kosakonia radicincitans GXGL-4A and visualization of bacterial colonization on cucumber roots.

A gram-negative bacterium GXGL-4A was originally isolated from maize roots. It displayed nitrogen-fixing (NF) ability under nitrogen-free culture condition, and had a significant promotion effect on cucumber growth in the pot inoculation test. The preliminary physiological and biochemical traits of GXGL-4A were characterized. Furthermore, a phylogenetic tree was constructed based on 16S ribosomal DNA (rDNA) sequences of genetically related species. To determine the taxonomic status of GXGL-4A and further utilize its nitrogen-fixing potential, genome sequence was obtained using PacBio RS II technology. The analyses of average nucleotide identity based on BLAST+ (ANIb) and correlation indexes of tetra-nucleotide signatures (Tetra) showed that the NF isolate GXGL-4A is closely related to the Kosakonia radicincitans type strain DSM 16656. Therefore, the isolate GXGL-4A was eventually classified into the species of Kosakonia radicincitans and designated K. radicincitans GXGL-4A. A high consistency in composition and gene arrangement of nitrogen-fixing gene cluster I (nif cluster I) was found between K. radicincitans GXGL-4A and other Kosakonia NF strains. The mutants tagged with green fluorescence protein (GFP) were obtained by transposon Tn5 mutagenesis, and then, the colonization of gfp-marked K. radicincitans GXGL-4A cells on cucumber seedling root were observed under fluorescence microscopy. The preferential sites of the labeled GXGL-4A cell population were the lateral root junctions, the differentiation zone, and the elongation zone. All these results should benefit for the deep exploration of nitrogen fixation mechanism of K. radicincitans GXGL-4A and will definitely facilitate the genetic modification process of this NF bacterium in sustainable agriculture.

Biological control tobacco bacterial wilt and black shank and root colonization by bio-organic fertilizer containing bacterium Pseudomonas aeruginosa NXHG29

Tobacco bacterial wilt (TBW) and tobacco black shank (TBS) are two of the most devastating tobacco soil-borne diseases worldwide. In this study, Pseudomonas aeruginosa NXHG29 exhibited dually antagonistic activities against TBW and TBS in vitro assays. Pot experiments were performed to evaluate the capability of a novel bio-organic fertilizer (BOF) consisting of organic fertilizer with NXHG29 to control TBW and TBS. The results showed that application of BOF could more effectively decrease the disease incidence of TBW and TBS than the direct application of NXHG29. Higher amounts of BOF application (0.5% and 1% amendment) resulted in the more suppressive effects on tested pathogens when compared with a low amount of BOF application (0.1% amendment). To determine the antagonistic mechanism of NXHG29, we investigated the colonization pattern of NXHG29 on tobacco roots in a sand system and a natural soil system by tagging NXHG29 with a GFP-marked plasmid. Similar observations were obtained in the two systems. The results indicated that GFP-tagged NXHG29 colonized first the differentiation zones followed by the elongation and maturation zones of the primary roots and subsequently around the junctions of primary and lateral roots. The population dynamics of GFP-tagged NXHG29 on tobacco roots and in the rhizosphere were also monitored. The development of the BOF using dually antagonistic bacteria might provide new options for control strategies, especially with respect to managing both diseases simultaneously in the host plant, which should be more effective in the long term.