Seminal Roots (seminal + root)

Distribution by Scientific Domains

Selected Abstracts

Effects of decreasing soil water content on seminal lateral roots of young maize plants


Abstract Soil micropores that contain water at or below field capacity cannot be invaded by seminal or first-order lateral roots of maize plants because their root diameters are larger than 10 ,m. Hence, at soil-water levels below field capacity plant roots must establish a new pore system by displacement of soil particles in order to access soil water. We investigated how decreasing soil water content (SWC) influences growth and morphology of the root system of young maize plants. Plants were grown in rhizotrons 40,cm wide, 50,cm high, and approximately 0.7,cm thick. Five SWC treatments were established by addition of increasing amounts of water to soil and thorough mixing before filling the rhizotrons. No water was added to treatments 1,4 throughout the experiment. Treatment 5 was watered frequently throughout the experiment to serve as a control. Seminal-root length and SWC in soil layers 0,10, 10,20, 20,30, 30,40, and 40,50,cm were measured at intervals of 2,3 d on scanner images by image analysis. At 15 d after planting, for treatments 1,4 shoot dry weight and total root length were directly related to the amount of water added to the soil, and for treatments 4 and 5, total root length and shoot dry weights were similar. Length of seminal roots visible at the transparent surface of the rhizotron for all treatments was highest in the uppermost soil layer and decreased with distance from the soil surface. For all layers, seminal-root elongation rate was at maximum above a SWC of 0.17,cm3,cm,3, corresponding to a matric potential of ,30 kPa. With decreasing SWC, elongation rate decreased, and 20% of maximum seminal root elongation rate was observed below SWC of 0.05,cm3,cm,3. After destructive harvest for treatment 1,4, number of (root-) tips per unit length of seminal root was found uninfluenced over the range of initial SWC from 0.10 to 0.26,cm3,cm,3. However, initial SWC close to the permanent wilting point strongly increased number of tips. Average root length of first-order lateral (FOL) roots increased as initial SWC increased, and the highest length was found for the frequently watered treatment 5. The results of the study suggest that the ability to produce new FOL roots across a wide range of SWC may give maize an adaptive advantage, because FOL root growth can rapidly adapt to changing soil moisture conditions. [source]

Use of a site-specific recombination-based biosensor for detecting bioavailable toluene and related compounds on roots

N. Carol Casavant
Summary We constructed and characterized a plasmid-based genetic system that reports the expression of a toluene-responsive promoter (PtbuA1) by effecting an irreversible, heritable change in the biosensor cell. Expression of the reporter gene gfp is strongly repressed in the absence of expression from the PtbuA1 promoter, and high level gfp expression in the original cell and its progeny is mediated by the site-specific recombination machinery of bacteriophage P22 to initiate removal of a repressor cassette. The reporter plasmid pTolLHB was functional in two soil saprophytes, Pseudomonas fluorescens A506 and Enterobacter cloacae JL1157, with the efficiency and sensitivity to low toluene concentrations being optimal in P. fluorescens A506. In culture, 80,100% of the A506 (pTolLHB) population expressed gfp following exposure to 0.2 µm toluene for one to three hours. Compared to the response of A506 containing a plasmid-borne PtbuA1 - gfp fusion, the recombination-based biosensor was more sensitive at detecting low toluene and trichloroethylene concentrations. An A506 (pTolLHB) inoculum, which had a background of 2.5% of the cells expressing gfp, was introduced onto barley roots in soil microcosms. If toluene was introduced into the microcosms, after 24 h, 72% of the A506 (pTolLHB) cells recovered from roots expressed gfp, indicating bioavailable toluene to rhizosphere bacteria. When toluene was not introduced, 16.5% of the A506 (pTolLHB) cells recovered from the roots expressed gfp, indicating that natural inducers of the PtbuA1 promoter were present in the barley rhizosphere. When introduced into rhizotrons containing barley plants and toluene vapours, the biosensor allowed localization of the availability of toluene along the seminal roots. In rhizotrons that were not exposed to toluene vapours, the biosensor exhibited high PtbuA1 -promoter activity in distinct regions along the seminal roots, indicating spatial heterogeneity plant- or rhizosphere microbial community-derived inducers of the PtbuA1 promoter. This recombination-based toluene biosensor thus was useful in identifying bacterial exposure to transient or low levels of toluene, or related compounds, directly in the environment. [source]

Identity and Pathogenicity of Fungi Associated with Root and Crown Rot of Soft Red Winter Wheat Grown on the Upper Coastal Plain Land Resource Area of Mississippi

M. S. Gonzalez
Seedling stand, disease severity and fungal incidence were determined from untreated ,Wakefield' soft red winter wheat planted on a Leeper silty clay loam in field tests conducted at the Mississippi Agricultural and Forestry Experiment Station, Plant Science Research Center, Mississippi State University, Starkville, Mississippi during the 1996,97 and 1997,98 growing seasons. Seedling stand was reduced by 40% each year in plots established with untreated seed. Cochliobolus sativus was the most frequently isolated fungus. Fusarium acuminatum, Fusarium equiseti and Fusarium solani were the most prevalent Fusarium spp. Seven other Fusarium spp. and 23 species of other fungal genera were isolated. Pathogenicity tests with three isolates each of C. sativus, Cochliobolus spicifer, F. acuminatum, F. solani, F. equiseti, Fusarium compactum, Embellisia chlamydospora and Microdochium bolleyi were performed in test tube culture and two isolates each of C. sativus, C. spicifer, F. acuminatum, E. chlamydospora and M. bolleyi under greenhouse conditions. In test tubes and in the greenhouse, seedlings infected with isolates of C. sativus developed seedling blight, discoloration and necrosis, primarily in seminal roots and crowns. In the greenhouse, C. sativus induced lesions on the lower leaf sheath and reduced seedling height, seedling emergence, dry and fresh weight of roots and shoots. Isolates of F. acuminatum, F. solani, F. equiseti, F. compactum, E. chlamydospora and M. bolleyi induced slight to moderate orange to light-brown discoloration of crown and seminal roots in test tubes. Cochliobolus spicifer isolates had the most pre-emergence activity, inducing black root discoloration and root pruning of wheat seedlings and reducing seedling emergence, root fresh weight and shoot dry weight. In the greenhouse, F. acuminatum reduced seedling height, seedling emergence and root and shoot dry weights. Microdochium bolleyi and E. chlamydospora reduced fresh and dry weight of roots, plant emergence and shoot dry weight. Fusarium acuminatum and C. spicifer reduced the growth rate of wheat seedlings. All fungi evaluated showed increased disease severity compared to the untreated control. The high frequency of isolation of C. sativus from crown and root tissues can be partially explained by the dry, warm conditions during the early stages of wheat seedling development in the Upper Coastal Plain Land Resource Area of Mississippi. Zusammenfassung Die Auflaufrate von Sämlingen, die Stärke des Krank-heitsbefalls sowie die Häufigkeit von Pilzarten wurden bei nicht behandelten roten Weichwinterweizen der Sorte Wakefield ermittelt, welche in einem Leeper schlammigen Tonboden an der Mississippi Agricultural & Forestry Experiment Station, Plant Science Research Center, Mississippi State University, Starkville, Mississippi in der 1996,97 und 1997,98 Saison gesät worden waren. In beiden Jahren wurde die Auflaufrate von nicht behandeltem Saatgut um 40% reduziert. Cochliobolus sativus wurde am häufigsten isoliert. Fusarium acuminatum, Fusarium equiseti und Fusarium solani waren die überwiegenden Fusarium spp. Außierdem wurden sieben weitere Fusarium spp. sowie 23 weitere Pilzarten isoliert. Pathogenitätstests mit je 3 Isolaten von C. sativus, Cochliobolus spicifer, F. acuminatum, F. solani, F. equiseti, Fusarium compactum, Embellisia chlamydospora und Microdochiumbolleyi wurden in Reagenzröhrchen durchgeführt, sowie mit je 2 Isolaten von C. sativus, C. spicifer, F. acuminatum, E. chlamydospora und M. bolleyi unter Gewächshausbedingungen. Sowohl in den Reagenzröhrchen als auch im Gewächshaus entwickelten Sämlinge, die mit C. sativus inokuliert worden waren, eine Fäule, Verfärbung sowie Nekrosis, hauptsächlich in den sekundären Wurzeln und in den Halmbasen. Unter Gewächshausbedingungen verursachte C. sativus außierdem Läsionen der unteren Blattscheide sowie eine Reduzierung des Sämlingswachstums, des Sämlingsauflaufs, des Trocken-und Frischgewichts der Wurzeln und Sprossen. Im Reagenzröhrchentest induzierten Isolate von F. acuminatum, F. solani, F. equiseti, F. compactum, E. chlamydospora und M. bolleyieine schwache bis mäßiige orange bis hell braune Verfärbung des Halmbasis und der Sekundärwurzeln. Isolate von C. spicifer besaßien die höchste Vorauflaufaktivität und induzierten eine Verschwärzung und Verkürzung der Wurzeln sowie eine Reduzierung des Sämlingsauflaufs, des Wurzelfrischgewichts sowie des Sproitrockengewichts. Unter Gewächshausbedingungen reduzierte F. acuminatum die Sämlingshöhe, die Auflaufrate sowie das Trockengewicht der Wurzeln und Sproien. Microdochium bolleyi und E. chlamydospora reduzierten das Frisch-und Trockengewicht der Wurzeln, die Auflaufrate sowie das Sproßitrockengewicht. Die Wachstumsrate der Sämlinge wurde durch F. acuminatum und C. spicifer reduziert. Alle untersuchten Pilzarten erhöhten die Befallsstärke verglichen mit der unbehandelten Kontrolle. Die hohe Isolierungsrate von C. sativus aus dem Halmbasis-und Wurzelgewebe kann zum Teil dadurch erklärt werden, dass während der Frühentwicklungsphase der Sämlinge trockene und warme Wachstumsbedingungen in diesem Gebiet herrschten. [source]

Effects of soil bulk density on seminal and lateral roots of young maize plants (Zea mays L.)

Rolf O. Kuchenbuch
Abstract It is well established that increasing soil bulk density (SBD) above some threshold value reduces plant root growth and thus may reduce water and nutrient acquisition. However, formation and elongation of maize seminal roots and first order lateral (FOL) roots in various soil layers under the influence of SBD has not been documented. Two studies were conducted on a loamy sand soil at SBD ranging from 1.25 g,cm,3 to 1.66 g,cm,3. Rhizotrons with a soil layer 7 mm thick were used and pre-germinated plants were grown for 15 days. Over the range of SBD tested, the shoot growth was not influenced whereas total root length was reduced by 30,% with increasing SBD. Absolute growth rate of seminal roots was highest in the top soil layer and decreased with increasing distance from the surface. Increasing SBD amplified this effect by 20,% and 50,% for the top soil layer and lower soil layers, respectively. At the end of the experiment, total seminal roots attributed to approximately 15,% of the total plant root length. Increasing SBD reduced seminal root growth in the lowest soil layer only, whereas FOL root length decreased with SBD in all but the uppermost soil layer. For FOL, there was a positive interaction of SBD with distance from the soil surface. Both, increasing SBD and soil depth reduced root length by a reduction of number of FOL roots formed while the length of individual FOL roots was not influenced. Hence, increasing SBD may reduce spatial access to nutrients and water by (i) reducing seminal root development in deeper soil layers, aggravated by (ii) the reduction of the number of FOL roots that originate from these seminal roots. Einfluss der Bodendichte auf Seminal- und Lateralwurzeln von jungen Maispflanzen (Zea mays L.) Es ist bekannt, dass zunehmende Bodendichte (SBD) oberhalb eines Grenzwertes das Wurzelwachstum von Pflanzen und die Wasser- und Nährstoffaufnahme reduziert. Bildung und Wachstum der Seminal- und der Lateralwurzeln erster Ordnung (FOL) von Mais in Bodenschichten verschiedenen Abstands von der Bodenoberfläche unter dem Einfluss verschiedener Bodendichten wurde bisher nicht beschrieben. Zwei unabhängige Versuche wurden mit einem lehmigen Sandboden durchgeführt. Vorgekeimte Maiskörner wurden in Rhizotrone mit einer etwa 7,mm dicken Bodenschicht eingesetzt, die Bodendichten lagen im Mittel der Rhizotrone zwischen 1,25 g,cm,3 und 1,66 g,cm,3. Die Versuchsdauer betrug 15 Tage. Über den Bereich der geprüften SBD wurde das Sprosswachstum nicht beeinflusst, während die Gesamtwurzellänge mit zunehmender SBD um bis zu 30,% abnahm. Die absolute Wachstumsrate der Seminalwurzeln war in der obersten Bodenschicht am höchsten und nahm mit zunehmendem Abstand von der Bodenoberfläche ab. Seminalwurzeln trugen zu ca. 15,% zur Gesamtwurzellänge bei. Zunehmende SBD reduzierte das Wachstum der Seminalwurzeln nur in der untersten Bodenschicht. Demgegenüber wurden die Längen der FOL in allen außer der obersten Schicht bei zunehmender SBD verringert. Bei den FOL wurde eine positive Interaktion zwischen SBD und Abstand von der Bodenoberfläche festgestellt. Sowohl zunehmende SBD als auch zunehmende Tiefe reduzierte die Wurzellänge durch eine Verringerung der Anzahl an FOL, während deren Länge nicht beeinflusst wurde. Folglich kann zunehmende SBD die räumliche Zugänglichkeit zu Wasser und Nährstoffen für die Pflanzen dadurch beeinflussen, dass (i) die Entwicklung von Seminalwurzeln in tieferen Bodenschichten reduziert wird und dass dieser Effekt verstärkt wird durch (ii) die verringerte Bildung von FOL an Seminalwurzeln. [source]

Short episodes of water stress increase barley root resistance to radial shrinkage in a dehydrating environment

Jorge Hugo Lemcoff
Although plant shoots can be ,hardened' by abiotic stresses, little is known about such changes in roots. In order to investigate possible induction of root-hardening in response to short water-stress episodes, barley seedlings (Hordeum vulgare L) hydroponically grown under a controlled environment were moderately water-stressed by addition of a non-penetrating osmoticum, polyethylene glycol (PEG) 6000 at ,0.4 MPa water potential, to the aerated nutrient solution. Seedlings were then hydrated in dilute nutrient solution without PEG before excision and assay of the seminal roots. Previous water stress treatments for 72 h, 12 h, or even 6 h induced an apparent root-hardening process. Thus, root radial shrinkage during subsequent exposure to strongly dehydrating conditions was remarkably decreased. The root hardening was related to biophysical adjustments: turgor-pressure increased while osmotic potential decreased from ,0.45 ± 0.02 MPa to ,0.60 ± 0.02 MPa. Moreover, the maximum bulk volumetric modulus of elasticity, ?max determined by pressure,volume analysis, increased from 2.1 ± 0.4 MPa to 3.7 ± 0.4 MPa, i.e. root elasticity was decreased. Root hardening in response to episodes of water stress may have ecological significance for barley plants in regions where intermittent drought episodes are frequent. [source]

Size, shape and intensity of aggregation of take-all disease during natural epidemics in second wheat crops

M. Gosme
Point pattern analysis (fitting of the beta-binomial distribution and binary form of power law) was used to describe the spatial pattern of natural take-all epidemics (caused by Gaeumannomyces graminis var. tritici) on a second consecutive crop of winter wheat in plots under different cropping practices that could have an impact on the quantity and spatial distribution of primary inoculum, and on the spread of the disease. The spatial pattern of take-all was aggregated in 48% of the datasets when disease incidence was assessed at the plant level and in 83% when it was assessed at the root level. Clusters of diseased roots were in general less than 1 m in diameter for crown roots and 1,1·5 m for seminal roots; when present, clusters of diseased plants were 2,2·5 m in diameter. Anisotropy of the spatial pattern was detected and could be linked to soil cultivation. Clusters did not increase in size over the cropping season, but increased spatial heterogeneity of the disease level was observed, corresponding to local disease amplification within clusters. The relative influences of autonomous spread and inoculum dispersal on the size and shape of clusters are discussed. [source]

The maize (Zea mays L.) RTCS gene encodes a LOB domain protein that is a key regulator of embryonic seminal and post-embryonic shoot-borne root initiation

Graziana Taramino
Summary Maize has a complex root system composed of different root types formed during different stages of development. The rtcs (rootless concerning crown and seminal roots) mutant is impaired in the initiation of the embryonic seminal roots and the post-embryonic shoot-borne root system. The primary root of the mutant shows a reduced gravitropic response, while its elongation, lateral root density and reaction to exogenously applied auxin is not affected. We report here the map-based cloning of the RTCS gene which encodes a 25.5 kDa LOB domain protein located on chromosome 1S. The RTCS gene has been duplicated during evolution. The RTCS-LIKE (RTCL) gene displays 72% sequence identity on the protein level. Both genes are preferentially expressed in roots. Expression of RTCS in coleoptilar nodes is confined to emerging shoot-borne root primordia. Sequence analyses of the RTCS and RTCL upstream genomic regions identified auxin response elements. Reverse transcriptase-PCR revealed that both genes are auxin induced. Microsynteny analyses between maize and rice genomes revealed co-linearity of 14 genes in the RTCS region. We conclude from our data that RTCS and RTCL are auxin-responsive genes involved in the early events that lead to the initiation and maintenance of seminal and shoot-borne root primordia formation. [source]