Root Axis Research Articles

Clinical and Radiographic Characteristics of Vertical Root Fractures in Endodontically and Nonendodontically Treated Teeth

IntroductionA vertical root fracture (VRF) is a root fracture extending along the longitudinal axis of roots and is often noted in endodontically treated teeth. However, the clinical and radiographic characteristics of VRFs are not completely known. MethodsA total of 65 teeth with 68 vertical fractured roots in 58 Chinese patients were investigated. The clinical examination records and radiographic images were reviewed in detail. ResultsA total of 24 male (41.38%) and 34 female (58.62%) patients aged 25–90 years (average = 57 years) were included; 51 (87.93%) and 7 (12.07%) patients exhibited 1 tooth and 2 teeth with VRFs, respectively, in the dentition. VRFs occurred mainly in the mesial root (20 roots, 57.14%) of the mandibular molars (29 teeth, 44.62%). Clinically, teeth with VRFs usually presented a periodontal probing depth >5 mm (44 teeth, 91.67%, P < .001) with a prosthesis (55 teeth, 84.62%, P < .001) and a relatively intact dentition (42 patients exhibited <4 missing teeth in the dentition, 77.78%, P < .001). Most of the nonendodontically treated VRFs exhibited attrited occlusal surfaces. Radiographic characteristics of the teeth with VRFs were typically associated with prior root canal treatment (56 teeth, 86.15%, P < .001), periodontal bone loss (62 teeth, 95.38%, P < .001), apical bone loss (52 teeth, 80.00%, P < .001), and periodontal ligament widening (61 teeth, 93.85%, P < .001). The mesial roots of the mandibular molars were most susceptible to VRFs in both endodontically and nonendodontically treated teeth. ConclusionsThese results elucidated some clinical and radiographic and diagnostic features that facilitate VRF identification.

Towards quantitative root hydraulic phenotyping: novel mathematical functions to calculate plant-scale hydraulic parameters from root system functional and structural traits

Predicting root water uptake and plant transpiration is crucial for managing plant irrigation and developing drought-tolerant root system ideotypes (i.e. ideal root systems). Today, three-dimensional structural functional models exist, which allows solving the water flow equation in the soil and in the root systems under transient conditions and in heterogeneous soils. Yet, these models rely on the full representation of the three-dimensional distribution of the root hydraulic properties, which is not always easy to access. Recently, new models able to represent this complex system without the full knowledge of the plant 3D hydraulic architecture and with a limited number of parameters have been developed. However, the estimation of the macroscopic parameters a priori still requires a numerical model and the knowledge of the full three-dimensional hydraulic architecture. The objective of this study is to provide analytical mathematical models to estimate the values of these parameters as a function of local plant general features, like the distance between laterals, the number of primaries or the ratio of radial to axial root conductances. Such functions would allow one to characterize the behaviour of a root system (as characterized by its macroscopic parameters) directly from averaged plant root traits, thereby opening new possibilities for developing quantitative ideotypes, by linking plant scale parameters to mean functional or structural properties. With its simple form, the proposed model offers the chance to perform sensitivity and optimization analyses as presented in this study.

Experimental and numerical investigation of liquid–solid binary fluidized beds: Radioactive particle tracking technique and dense discrete phase model simulations

Liquid–solid binary fluidized beds are widely used in many industries. However, the flow behavior of such beds is not well understood due to the lack of accurate experimental and numerical data. In the current study, the behavior of monodisperse and binary liquid–solid fluidized beds of the same density but different sizes is investigated using radioactive particle tracking (RPT) technique and a dense discrete phase model (DDPM). Experiments and simulations are performed in monodisperse fluidized beds containing two different sizes of glass beads (0.6 and 1mm) and a binary fluidized bed of the same particles for various bed compositions. The results show that both RPT and DDPM can predict the mixing and segregation pattern in liquid–solid binary fluidized beds. The mean velocity predictions of DDPM are in good agreement with the experimental findings for both monodisperse and binary fluidized beds. However, the axial root mean square velocity predictions are only reasonable for bigger particles. Particle–particle interactions are found to be critical for predicting the flow behavior of solids in liquid–solid binary fluidized beds.

Repair of root canal perforation by different materials

Background: The aim of this in vitro study was to compare sealing ability of Mineral Trioxide Aggregate (MTA), Glass ionomer cement (GIC) and Epiphany obturation system in repairing the iatrogenic lateral root canal perforation. Materials and Methods: Thirty freshly extracted human teeth with single and straight canals were used in this study. These teeth were cleaned and their crowns were removed at the cemento-enamel junction. The roots were instrumented using the step-back technique. A perforation was created on the mesial root surface at about 45- degree angle to the long axis of each root apico-coronally at the middle third by small round bur #1/2 with copious irrigation of 2.5% NaOCL and 17% buffered solution of EDTA was used as the final rinse to remove the smear layer and to prevent the blockage of perforation. The 30 roots were divided randomly in to three groups (10 roots for each group):- Group A: The root canal perforation was repaired by MTA then obturated by lateral condensation technique with gutta-percha and zinc oxide eugenol sealer. Group B: The root canal perforation was repaired by GIC then obturated by lateral condensation technique with gutta-percha and zinc oxide eugenol sealer. Group C: the roots were obturated with Epiphany obturation system by lateral condensation technique. The external surfaces of all roots were coated by two layers of sticky wax except the perforation site then immersed in 2% methylene blue dye for 48 hrs in incubator at 37C°. After that all roots were longitudinally sectioned for linear measurement of dye penetration through the perforation using a stereomicroscope at X40 magnification with calibrated scale ocular grid. Results: The result showed that group A showed the lowest mean of dye leakage (0.77mm) while group C showed the highest mean of dye leakage (4.45mm). Conclusion: Significantly less dye leakage in roots which perforations repaired by MTA than those repaired by GIC and highly significant less dye leakage than those repaired by Epiphany obturation system.

Influence of Post Angulation between Coronal and Radicular Segment on the Fracture Resistance of Endodontically Treated Teeth.

The objectives of coronal restoration in the Endodontically Treated Teeth (ETT) include rehabilitation of aesthetics, function and prevention of coronal leakage. The long axis of root and the coronal segment in the maxillary anterior teeth varies according to the occlusal scheme. The restorative dentist is required to fabricate the post angulation in compatibility to contour of the adjacent teeth. To evaluate the influence of the angle between the long axes of core facial surface and the radicular segment of the post on fracture resistance of ETT. Total of 30 maxillary intact canines was root canal treated, sectioned 2 mm above the CEJ. The custom made nickel-chromium endodontic posts were fabricated using direct method. The samples were divided among three groups of 10 each. The angle between coronal segment and radicular segment of post in Group-I, Group-II, Group-III were 5°, 10° and 15° respectively. The teeth samples were cemented with full veneer metal crown and tested under universal testing machine. The static load at the angle of 130° was applied until the fracture to record the fracture strength. The obtained data was statistically analysed with ANOVA and Tukey post-hoc test. The Group-III showed the highest fracture strength with 666.15 N. The Group-II and Group-I recorded the mean fracture strength at 443.37 N and 276.74 N respectively. The endodontic post with higher angle between the long axis of facial surface and radicular segment long axis had the positive correlation to the fracture strength in ETT.

Remineralization ability of sodium fluoride on the microhardness of enamel, dentin, and dentinoenamel junction: An in vitro study.

Aim:Dental tissues such as enamel, dentinoenamel junction (DEJ), dentin, and root dentin can react differently to demineralization and remineralization. The aim of this study was to evaluate the remineralization ability of sodium fluoride on the microhardness of enamel, dentin, and dentinoenamel junction.Materials and Methods:Ten extracted third molar teeth were sectioned mesiodistally to form control and test groups. For the test group, initial demineralization was done with acetic acid for 24 h followed by remineralization for 28 days by application of sodium fluoride (226 ppm) for 2 min twice a day. Vickers microhardness test was done to control and test groups at different sites after initial demineralization and on the 3rd, 5th, 7th, 14th, and 28th day of remineralization.Statistical Analysis Used:Data were analyzed with one-way analysis of variance and post hoc test with a significance level of P < 0.001 with SPSS (21) software.Results:Microhardness values in the demineralization group were significantly lower than controls (P < 0.001). Evaluation of remineralization samples showed that microhardness similar to control values were achieved at the 3rd day in root predentin and on the 5th day in coronal dentin and coronal predentin. On the 7th day, remineralization coronal predentin was significantly higher than the control (P < 0.001). On the 14th day, DEJ axial zone and root dentin were similar to control and coronal dentin was significantly higher than the control (P < 0.001). Enamel was similar to control on the 28th day. Microhardness of DEJ-cusp tip and DEJ-center of the fissure was significantly lower than control even at the 28th day (P < 0.001).Conclusion:Long-term repeated application of sodium fluoride (226 ppm) can improve the microhardness of demineralized dental tissues on enamel, dentin, and DEJ-axial zone, except in the DEJ-cusp tip and DEJ-center of fissure.

Fracture Resistance of Tilted Premolars Restored with Different Post-Core Systems.

Aims and Objective:To assess the effect of root tilt on the fracture resistance and failure pattern of endodontically-treated premolars restored with different post-core systems.Materials and Methods:Ninety endodontically-treated premolars were mounted in acrylic blocks with 0°, 12°, and 24° axial root tilt. Teeth in each group were restored in three subgroups with cast post-core, readymade metal posts and composite cores, and fiber post and composite cores. Crowns of all teeth were prepared coinciding with the long axis of the acrylic blocks to receive all-ceramic crowns. All restored teeth were stressed to record the maximum load at failure and the associated failure pattern. The collected data were statistically analyzed using two-way ANOVA, Tukey's, and Kruskal–Wallis tests at α = 0.05 on past software to detect any differences between subgroups.Results:Analysis of the collected data indicated significant differences between the tested subgroups (ANOVA, P = 3.86). Further analysis showed significant difference between all test subgroups and the control (Tukey's, P < 0.05). In general, teeth with 0° tilt seemed more resistant to fracture than the tilted ones. For all groups, teeth restored with fiber post and composite cores (SG3) were more resistant to fracture compared to other post-core systems (SG1 and SG2) (Tukey's, P < 0.05). The root fracture was the most commonly seen mode of failure.Conclusions:Root tilting usually affects the fracture resistance of teeth restored with post-core systems. The fiber post and composite cores seemed to be the best choice to restore teeth with different root tilting possibilities.

Ammonia/Ammonium Toxicity Root Symptoms Induced by Inorganic and Organic Fertilizers and Placement

Ammoniacal fertilizers can cause seedling damage. The present aims were to characterize spatial and temporal, root morphological NH3/NH4+ toxicity symptoms, assess the extent of the toxicity zone, and relate species‐specific responses to their root architecture. Wheat (Triticum aestivum L.) and canola (Brassica napus L.) were exposed to seed and deep placed urea. Faba (Vicia faba L) seedlings were grown above organic amendments. Time‐sequential images of canola root apex and root hair die‐back, discoloration, and accelerated lateral rooting were captured with soil‐buried, high resolution digital scanners. Seed‐placed urea stunted wheat shoot and root radicles, while slow‐release urea reduced these symptoms. Primary axes of all three species were damaged by encountering the deep fertilizer zones. The multiple seminal axes and lateral root growth away from the fertilizer allowed greater wheat seedling survival, while toxicity‐damage to a single tap root of the germinating canola and faba often resulted in seedling mortality. Urea and chicken manure developed expanded NH3/NH4+ toxicity zones 1.5 to 5 cm, eliciting similar toxicity symptoms initiated at the root apex. Within 3 d after planting, canola tap root elongation stopped, followed by progressive basal directed necrosis and shrinking of the root axis, root hairs. These characteristic symptoms may be used for future toxicity diagnostics of soil‐grown plants. Elevated pH in the soil zone above the chicken manure suggested NH3 gas transported through soil pores followed by H+ consumption and elevated NH4+. Ammonia gas toxicity and species‐specific root system architecture should be considered in N placement and source selection.Core Ideas NH3/NH4+ toxicity initiates at the root apex and moves basipetally. Symptoms include tissue discoloration, axis shrinkage, root hair disfigurement, and seedling death. Toxicity zones ranged from 1 to 5 cm from the ammonia sources. Putative upward movement of ammonia raised soil pH and NH4+ above chicken manure. Most wheat axes avoided NH3/NH4+ toxicity zones, improving survival over tap‐rooted species.

Ácido sulfúrico na quebra de dormência de sementes e na emergência e morfologia de plântulas de Canna edulis

he objective of this study was to evaluate the efficiency of time scarification of seeds in sulfuric acid to break the dormancy of seeds, seedling emergence and post-seminal morphology of C. edulis. This way, were determined biometric characteristics of seeds with the help of pachymeter and digital balance. To dormancy breaking, the seeds were immersed in sulfuric acid during 0.0, 0.5, 1.0, 1.5, 2.0 and 2.5 hours and sown in sand in a condition greenhouse. After 21 days emergence percentage, emergence speed index (IVE), shoot length and seedling dry weight of plants were recorded. At 0, 2, 4, 8, 12, 16, 20 days after sowing, the seedlings taken digital images and post-seminal morphology was characterized. The fruit of C. edulis contains an average of 19.27 globoses seeds of black coloration measuring about 5.62 mm in diameter, the average weight of 1000 seeds is 128.8 grams. The highest percentage of seedling emergence of 60% and 90% are obtained from seed treated with 0.5 hours in sulfuric acid at 10 and 21 days after sowing, respectively. The seeds have hypogeal germination with development of fasciculate roots with root axes differentiated at 4 days after sowing. The protophyll is observed from the eighth day and the seedlings have intense purple coloration at 16 days after sowing.

Root-hair endophyte stacking in finger millet creates a physicochemical barrier to trap the fungal pathogen Fusarium graminearum

The ancient African crop, finger millet, has broad resistance to pathogens including the toxigenic fungus Fusarium graminearum. Here, we report the discovery of a novel plant defence mechanism resulting from an unusual symbiosis between finger millet and a root-inhabiting bacterial endophyte, M6 (Enterobacter sp.). Seed-coated M6 swarms towards root-invading Fusarium and is associated with the growth of root hairs, which then bend parallel to the root axis, subsequently forming biofilm-mediated microcolonies, resulting in a remarkable, multilayer root-hair endophyte stack (RHESt). The RHESt results in a physical barrier that prevents entry and/or traps F. graminearum, which is then killed. M6 thus creates its own specialized killing microhabitat. Tn5-mutagenesis shows that M6 killing requires c-di-GMP-dependent signalling, diverse fungicides and resistance to a Fusarium-derived antibiotic. Further molecular evidence suggests long-term host-endophyte-pathogen co-evolution. The end result of this remarkable symbiosis is reduced deoxynivalenol mycotoxin, potentially benefiting millions of subsistence farmers and livestock. Further results suggest that the anti-Fusarium activity of M6 may be transferable to maize and wheat. RHESt demonstrates the value of exploring ancient, orphan crop microbiomes.

Mature zygotic embryo rescue improves in vitro germination and seedling production in high value oil palm (Elaeis guineensis Jacq.) cultivars

The world production of palm oil has been increasing at a rapid rate due to its overwhelming demand for edible oils and oil products, oleo-chemicals and for clean transportation energy fuel. The lengthy germination period of oil palm seeds presents a major drawback for the production and supply of seedlings at commercial level. The present study was therefore, carried out to appraise the in vitro germination potential of mature zygotic embryos (MZE) of 10 Tenera oil palm cultivars (CV 1–10). In vitro germination aptitude of MZE was tested on 10 modified Murashige and Skoog (MS) culture media (CM1-10). All the ten CV showed positive response to germination between 7–20 days. Nonetheless, significant (P≤0.05) differences in germination percentage and organogenesis were noticed between CV and culture media. CV1 and CV5 scored the highest germination rate (90%) while the least germination rate of 14% was recorded in CV8. The most suitable culture medium (CM5) registered 72% germination while the least (48%) was observed in CM1 and CM8. The most robust plantlets with complete differentiation into a shoot and root axis occurred in CM2, CM5, CM7 and CM10. Complementing this embryo rescue with conventional method could help to scale up seed germination and through large-scale implementation boost seed production potential of oil palm hybrids.

Poplar woody taproot under bending stress: the asymmetric response of the convex and concave sides.

Background and Aims Progress has been made in understanding the physiological and molecular basis of root response to mechanical stress, especially in the model plant Arabidopsis thaliana, in which bending causes the initiation of lateral root primordia toward the convex side of the bent root. In the case of woody roots, it has been reported that mechanical stress induces an asymmetric distribution of lateral roots and reaction wood formation, but the mechanisms underlying these responses are largely unknown. In the present work, the hypothesis was tested that bending could determine an asymmetric response in the two sides of the main root axis as cells are stretched on the convex side and compressed on the concave side. Methods Woody taproots of 20 seedlings were bent to an angle of 90° using a steel net. Changes in the anatomy, lignin and phytohormone content and proteome expression in the two sides of the bent root were analysed; anatomical changes, including dissimilarities and similarities to those found in poplar bent woody stem, were also considered. Key Results Compression forces at the concave side of poplar root induced the formation of reaction wood which presented a high lignin content and was associated with the induction of cambium cell activity. Auxin seemed to be the main hormone triggering lignin deposition and cell wall strengthening in the concave sides. Abscisic acid appeared to function in the water stress response induced by xylem structures and/or osmotic alterations in the compression sides, whereas gibberellins may control cell elongation and gravitropisms. Conclusions Poplar root reaction wood showed characteristics different from those produced in bent stem. Besides providing biomechanical functions, a bent root ensures water uptake and transport in the deforming condition induced by tension and compression forces by two different strategies: an increase in xylem thickness in the compressed side, and lateral root formation in the tension side.

Impact of axial root growth angles on nitrogen acquisition in maize depends on environmental conditions.

Crops with reduced requirement for nitrogen (N) fertilizer would have substantial benefits in developed nations, while improving food security in developing nations. This study employs the functional structural plant model SimRoot to test the hypothesis that variation in the growth angles of axial roots of maize (Zea mays L.) is an important determinant of N capture. Six phenotypes contrasting in axial root growth angles were modelled for 42 d at seven soil nitrate levels from 10 to 250 kg ha(-1) in a sand and a silt loam, and five precipitation regimes ranging from 0·5× to 1·5× of an ambient rainfall pattern. Model results were compared with soil N measurements of field sites with silt loam and loamy sand textures. For optimal nitrate uptake, root foraging must coincide with nitrate availability in the soil profile, which depends on soil type and precipitation regime. The benefit of specific root architectures for efficient N uptake increases with decreasing soil N content, while the effect of soil type increases with increasing soil N level. Extreme root architectures are beneficial under extreme environmental conditions. Extremely shallow root systems perform well under reduced precipitation, but perform poorly with ambient and greater precipitation. Dimorphic phenotypes with normal or shallow seminal and very steep nodal roots performed well in all scenarios, and consistently outperformed the steep phenotypes. Nitrate uptake increased under reduced leaching conditions in the silt loam and with low precipitation. Results support the hypothesis that root growth angles are primary determinants of N acquisition in maize. With decreasing soil N status, optimal angles resulted in 15-50 % greater N acquisition over 42 d. Optimal root phenotypes for N capture varied with soil and precipitation regimes, suggesting that genetic selection for root phenotypes could be tailored to specific environments.

Sowing Density: A Neglected Factor Fundamentally Affecting Root Distribution and Biomass Allocation of Field Grown Spring Barley (Hordeum Vulgare L.).

Studies on the function of root traits and the genetic variation in these traits are often conducted under controlled conditions using individual potted plants. Little is known about root growth under field conditions and how root traits are affected by agronomic practices in particular sowing density. We hypothesized that with increasing sowing density, root length density (root length per soil volume, cm cm−3) increases in the topsoil as well as specific root length (root length per root dry weight, cm g−1) due to greater investment in fine roots. Therefore, we studied two spring barley cultivars at ten different sowing densities (24–340 seeds m−2) in 2 consecutive years in a clay loam field in Germany and established sowing density dose-response curves for several root and shoot traits. We took soil cores for measuring roots up to a depth of 60 cm in and between plant rows (inter-row distance 21 cm). Root length density increased with increasing sowing density and was greatest in the plant row in the topsoil (0–10 cm). Greater sowing density increased specific root length partly through greater production of fine roots in the topsoil. Rooting depth (D50) of the major root axes (root diameter class 0.4–1.0 mm) was not affected. Root mass fraction decreased, while stem mass fraction increased with sowing density and over time. Leaf mass fraction was constant over sowing density but greater leaf area was realized through increased specific leaf area. Considering fertilization, we assume that light competition caused plants to grow more shoot mass at the cost of investment into roots, which is partly compensated by increased specific root length and shallow rooting. Increased biomass per area with greater densities suggest that density increases the efficiency of the cropping system, however, declines in harvest index at densities over 230 plants m−2 suggest that this efficiency did not translate into greater yield. We conclude that plant density is a modifier of root architecture and that root traits and their utility in breeding for greater productivity have to be understood in the context of high sowing densities.

Modification of the endogenous NO level influences apple embryos dormancy by alterations of nitrated and biotinylated protein patterns.

NO donors and Arg remove dormancy of apple embryos and stimulate germination. Compounds lowering NO level (cPTIO, L -NAME, CAN) strengthen dormancy. Embryo transition from dormancy state to germination is linked to increased nitric oxide synthase (NOS)-like activity. Germination of embryos is associated with declined level of biotin containing proteins and nitrated proteins in soluble protein fraction of root axis. Pattern of nitrated proteins suggest that storage proteins are putative targets of nitration. Nitric oxide (NO) acts as a key regulatory factor in removal of seed dormancy and is a signal necessary for seed transition from dormant state into germination. Modulation of NO concentration in apple (Malus domestica Borkh.) embryos by NO fumigation, treatment with NO donor (S-nitroso-N-acetyl-D,L-penicillamine, SNAP), application of 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO), N ω-nitro-L-arginine methyl ester (L-NAME), canavanine (CAN) or arginine (Arg) allowed us to investigate the NO impact on seed dormancy status. Arg analogs and NO scavenger strengthened embryo dormancy by lowering reactive nitrogen species level in embryonic axes. This effect was accompanied by strong inhibition of NOS-like activity, without significant influence on tissue NO2 (-) concentration. Germination sensu stricto of apple embryos initiated by dormancy breakage via short term NO treatment or Arg supplementation were linked to a reduced level of biotinylated proteins in root axis. Decrease of total soluble nitrated proteins was observed at the termination of germination sensu stricto. Also modulation of NO tissue status leads to modification in nitrated protein pattern. Among protein bands that correspond to molecular mass of approximately 95kDa, storage proteins (legumin A-like and seed biotin-containing protein) were identified, and can be considered as good markers for seed dormancy status. Moreover, pattern of nitrated proteins suggest that biotin containing proteins are also targets of nitration.

Genetic diversity and population structure among sorghum (Sorghum bicolor, L.) germplasm collections from Western Ethiopia

The mangrove sediments are rich in organic matter and humic substances, responsible for important functions such as reducing the toxicity of heavy metals, nutrient stabilization, serving as drain to atmospheric carbon and increasing the plant growth. In this study, we observed the effect of humic substances, humic acids and fulvic acids isolated from sediments of a mangrove forest, sampled from the Municipal Ecological Station Ilha do Lameirao (EEMIL, located in Vitoria, Espirito Santo State, Brazil), on the growth and root acidification of Rizophora mangle and Laguncularia racemosa seedlings. For this, R. mangle and L. racemosa propagules were transferred to pots and then treated with different humic materials. The evaluation in root architecture change was performed by analyzing the main root axis length, lateral root length, density of lateral roots, fresh and dry mass weight of roots and estimated H + -ATPase activity by specific root acidification measurement. The results indicate that all humic materials extracted from mangrove organic matter were able to modify the root architecture systems of the studied plants. In addition to inducing an increase in the number of lateral roots and root branching, it also stimulated specific root acidification when compared to control groups. There is a good potential in developing technologies for the production of seedlings of mangrove plant species treated with biostimulants based in humic materials isolated from the mangrove ecosystem itself. Keywords: Humic substances, humic acids, fulvic acids, mangrove

Three-dimensional imaging for indirect-direct bonding.

The aim of this article is to introduce a new concept of bracket positioning with special consideration to root axes. Cone-beam computed tomography imaging and computer-aided manufacturing were used to produce stereolithographic trays for indirect-direct bonding.

Estimation of runoff mitigation by morphologically different cover crop root systems

Summary Hydrology is a major driver of biogeochemical processes underlying the distinct productivity of different biomes, including agricultural plantations. Understanding factors governing water fluxes in soil is therefore a key target for hydrological management. Our aim was to investigate changes in soil hydraulic conductivity driven by morphologically different root systems of cover crops and their impact on surface runoff. Root systems of twelve cover crop species were characterized and the corresponding hydraulic conductivity was measured by tension infiltrometry. Relations of root traits to Gardner’s hydraulic conductivity function were determined and the impact on surface runoff was estimated using HYDRUS 2D. The species differed in both rooting density and root axes thickness, with legumes distinguished by coarser axes. Soil hydraulic conductivity was changed particularly in the plant row where roots are concentrated. Specific root length and median root radius were the best predictors for hydraulic conductivity changes. For an intensive rainfall simulation scenario up to 17% less rainfall was lost by surface runoff in case of the coarsely rooted legumes Melilotus officinalis and Lathyrus sativus , and the densely rooted Linum usitatissimum . Cover crops with coarse root axes and high rooting density enhance soil hydraulic conductivity and effectively reduce surface runoff. An appropriate functional root description can contribute to targeted cover crop selection for efficient runoff mitigation.

Salinity-induced reduction in root surface area and changes in major root and shoot traits at the phytomer level in wheat.

The aim of this study was to investigate the effect of salinity stress on root growth at the phytomer level in wheat to provide novel site-specific understanding of salinity damage in roots. Seedlings of 13 wheat varieties were grown hydroponically. Plants were exposed to three concentrations of NaCl, 0 (control), 50 and 100mM, from 47 days after sowing. In a destructive harvest 12 days later we determined the number of live leaves, adventitious roots, seminal roots and newly formed roots at the youngest phytomer; length and diameter of main axes; and length and diameter of root hairs and their number per millimetre of root axis. Elongation rate of main axes and root hair density were then derived. Root surface area at each root-bearing phytomer (Pr) was mechanistically modelled. New root formation was increased by salt exposure, while number of live leaves per plant decreased. The greatest salinity effect on root axis elongation was observed at the youngest roots at Pr1 and Pr2. Both the 50mM and the 100mM levels of salinity reduced root hair length by approximately 25% and root hair density by 40% compared with the control whereas root hairs alone contributed around 93% of the estimated total root surface area of an individual tiller. Decrease in main axis length of new roots, root hair density and root hair length combined to reduce estimated root surface area by 36-66% at the higher NaCl concentration. The varietal response towards the three salinity levels was found to be trait-specific. The data highlight reduction in root surface area as a major but previously largely unrecognized component of salinity damage. Salinity resistance is trait-specific. Selection for retention of root surface area at a specific phytomer position following salt exposure might be useful in development of salinity-tolerant crop varieties.

Salt Stress Affects the Redox Status of Arabidopsis Root Meristems.

We report the redox status (profiles) for specific populations of cells that comprise the Arabidopsis root tip. For recently germinated, 3–5-day-old seedlings we show that the region of the root tip with the most reduced redox status includes the root cap initials, the quiescent center and the most distal portion of the proximal meristem, and coincides with (overlays) the region of the auxin maximum. As one moves basally, further into the proximal meristem, and depending on the growth conditions, the redox status becomes more oxidized, with a 5–10 mV difference in redox potential between the two borders delimiting the proximal meristem. At the point on the root axis at which cells of the proximal meristem cease division and enter the transition zone, the redox potential levels off, and remains more or less unchanged throughout the transition zone. As cells leave the transition zone and enter the zone of elongation the redox potentials become more oxidized. Treating roots with salt (50, 100, and 150 mM NaCl) results in marked changes in root meristem structure and development, and is preceded by changes in the redox profile, which flattens, and initially becomes more oxidized, with pronounced changes in the redox potentials of the root cap, the root cap initials and the quiescent center. Roots exposed to relatively mild levels of salt (<100 mM) are able to re-establish a normal, pre-salt treatment redox profile 3–6 days after exposure to salt. Coincident with the salt-associated changes in redox profiles are changes in the distribution of auxin transporters (AUX1, PIN1/2), which become more diffuse in their localization. We conclude that salt stress affects root meristem maintenance, in part, through changes in redox and auxin transport.