Higher Elongation Rate Research Articles

Nitrogen Uptake and Allocation in Sweet Viburnum During a Root Growth Flush

ABSTRACT Most woody ornamentals exhibit episodic growth flushes and nitrogen (N) uptake has also been demonstrated to be seasonal. However, there is little information on N uptake in relationship to plant growth cycle. In this study, N uptake and allocation of sweet viburnum during periods of low and high root elongation rates were studied. Plants were fertilized with ammonium nitrate (15NH4 15NO3) and after 6 d N absorption was determined. Significantly more N was absorbed by plants with low root elongation rate compared with plants with high root elongation rate. About 70% of the N absorbed by plants with low root elongation rate was allocated to the mature leaves compared to 35% on plants with high root elongation rate. It was evident that root growth activity influenced N absorption and allocation. Although only a small amount of the N absorbed by plants with low root elongation rates was allocated to the immature leaves, significantly more N was allocated to the immature leaves by plants with high root elongation rates. It is possible that the N necessary to support immature leaf growth, when root elongation rate is low, is provided by mobilization from other parts, possibly mature leaves.

Micropropagation of Juniperus phoenicea from adult plant explants and analysis of ploidy stability using flow cytometry

We report here the successful micropropagation of adult Juniperus phoenicea L. with respective ploidy stability studies. Microcuttings with axillary buds were grown on five media supplemented with different growth regulator combinations. Best elongation rates were achieved on Driver and Kuniyuki (DKW) medium supplemented with kinetin alone or with naphthaleneacetic acid (NAA), while Rugini olive (OM) medium stimulated the development of new branches. Shoots growing on Murashige and Skoog (MS) medium browned and showed necrotic zones. Shoots of second to fourth subcultures usually had higher elongation rates than those of the first culture. For rooting assays, half strength DKW and OM media, different concentrations of growth regulators, auxin continuous exposure vs. dipping and the type of solid matrix were assessed. During rooting assays, two morphotypes were observed with one type having well developed internodes and the other showing hyperhydratation and no internode development. High rooting rates (40 %) were only obtained in the first morphotype shoots exposed for 5 min to 2.4 µM IBA and then transferred to OM medium without growth regulators. Plants were acclimatized in pots containing a mixture of peat and Perlite (3:2) in greenhouse with progressive reduction of relative humidity. A flow cytometric screening for major ploidy changes revealed no differences among the morphotypes and between them and the mother plant. Also the nuclear DNA content of this species was estimated for the first time using flow cytometry (2C = 24.71 pg).

Are source and sink strengths genetically linked in maize plants subjected to water deficit? A QTL study of the responses of leaf growth and of Anthesis-Silking Interval to water deficit

Leaf growth and Anthesis-Silking Interval (ASI) are the main determinants of source and sink strengths of maize via their relations with light interception and yield, respectively. They depend on the abilities of leaves and silks to expand under fluctuating environmental conditions, so the possibility is raised that they may have a partly common genetic determinism. This possibility was tested in a mapping population which segregates for ASI. Maximum leaf elongation rate per unit thermal time (parameter a) and the slopes of its responses to evaporative demand and soil water status (parameters b and c) were measured in greenhouse and growth chamber experiments, in two series of 120 recombinant inbred lines (RILs) studied in 2004 and 2005 with 33 RILs in common both years. ASI was measured in three and five fields under well-watered conditions and water deficit, respectively. For each RIL, the maximum elongation rate per unit thermal time was reproducible over several experiments in well-watered plants. It was accounted for by five QTLs, among which three co-localized with QTLs of ASI of well-watered plants. The alleles conferring high leaf elongation rate conferred a low ASI (high silk elongation rate). The responses of leaf elongation rate to evaporative demand and to predawn leaf water potential were linear, allowing each RIL to be characterized by the slopes of these response curves. These slopes had three QTLs in common with ASI of plants under water deficit. The allele for leaf growth maintenance was, in all cases, that for shorter ASI (maintained silk elongation rate). By contrast, other regions influencing ASI had no influence on leaf growth. These results may have profound consequences for modelling the genotype x environment interaction and for designing drought-tolerant ideotypes.

The NH2-terminal php Domain of the α Subunit of the Escherichia coli Replicase Binds the ϵ Proofreading Subunit

The alpha subunit of the replicase of all bacteria contains a php domain, initially identified by its similarity to histidinol phosphatase but of otherwise unknown function (Aravind, L., and Koonin, E. V. (1998) Nucleic Acids Res. 26, 3746-3752). Deletion of 60 residues from the NH2 terminus of the alpha php domain destroys epsilon binding. The minimal 255-residue php domain, estimated by sequence alignment with homolog YcdX, is insufficient for epsilon binding. However, a 320-residue segment including sequences that immediately precede the polymerase domain binds epsilon with the same affinity as the 1160-residue full-length alpha subunit. A subset of mutations of a conserved acidic residue (Asp43 in Escherichia coli alpha) present in the php domain of all bacterial replicases resulted in defects in epsilon binding. Using sequence alignments, we show that the prototypical gram+ Pol C, which contains the polymerase and proofreading activities within the same polypeptide chain, has an epsilon-like sequence inserted in a surface loop near the center of the homologous YcdX protein. These findings suggest that the php domain serves as a platform to enable coordination of proofreading and polymerase activities during chromosomal replication.

Structure Formation under Steady-State Isothermal Planar Elongational Flow ofn-Eicosane: A Comparison between Simulation and Experiment

We use nonequilibrium molecular dynamics simulations to investigate the structural properties of an oriented melt of n-eicosane under steady-state planar elongational flow. The flow-induced structure was evaluated using the structure factor s(k) taken as the Fourier transform of the total pair correlation function g(r). We found that the equilibrium liquid structure factor is in excellent agreement with the one determined via x-ray diffraction. Moreover, a new x-ray diffraction experiment has been performed on a crystalline n-eicosane sample. The resulting intramolecular contribution to the structure factor was found to be in very good agreement with the simulated one at a high elongation rate, indicating the existence of a possible crystalline precursor structure.

Pedestrian Injuries: Viscoelastic Properties of Human Knee Ligaments at High Loading Rates

Objective. Accidents involving pedestrians are very common, and often lead to severe injuries to the lower extremities. In a large portion of pedestrian-automobile collisions, knee ligament injuries are sustained. In this study, the viscoelastic properties of the four major human knee ligaments were investigated at loading rates representative for pedestrian-automobile collisions. Methods. Bone-ligament-bone specimens were tested in knee distraction loading. The collateral ligaments and the separate functional bundles of the cruciate ligaments were tested in the anatomical position corresponding to a fully extended knee. A series of step-and-hold tests and ramp tests at different rates were conducted to characterize the time-dependent behavior of the knee ligaments for deformation rates associated with the pedestrian impact loading environment. The quasi linear viscoelastic (QLV) theory was used to describe the structural response of the knee ligaments and averaged parameters for this model were determined. Results. The QLV theory was found to be applicable for the time range that is relevant for pedestrian-automobile collisions. The structural behavior of the knee ligaments was found to be particularly rate-sensitive for high elongation rates, as occur during these collisions. The ligament stiffness was found to increase with age for both the collateral ligaments and with weight for the medial collateral ligament. Conclusions. For the loading conditions that are relevant for pedestrian-automobile collisions, the use of the QLV model for the description of the mechanical behavior of knee ligaments is appropriate. The rate-sensitivity is particularly important for these extreme loading conditions. The relaxation behavior was found to be consistent between different ligament types and samples. Variations due to donor anthropometry were found predominantly for the instantaneous elastic behavior.

Rheological and structural studies of liquid decane, hexadecane, and tetracosane under planar elongational flow using nonequilibrium molecular-dynamics simulations

We report for the first time rheological and structural properties of liquid decane, hexadecane, and tetracosane using nonequilibrium molecular-dynamics (NEMD) simulations under planar elongational flow (PEF). The underlying NEMD algorithm employed is the so-called p-SLLOD algorithm [C. Baig, B. J. Edwards, D. J. Keffer, and H. D. Cochran, J. Chem. Phys. 122, 114103 (2005)]. Two elongational viscosities are measured, and they are shown not to be equal to each other, indicating two independent viscometric functions in PEF. With an appropriate definition, it is observed that the two elongational viscosities converge to each other at very low elongation rates, i.e., in the Newtonian regime. For all three alkanes, tension-thinning behavior is observed. At high elongation rates, chains appear to be fully stretched. This is supported by the result of the mean-square end-to-end distance of chains (R(ete2)) and the mean-square radius of gyration of chains (R(g2)), and further supported by the result of the intramolecular Lennard-Jones (LJ) potential energy. It is also observed that (R(ete2)) and (R(g2)) show a different trend as a function of strain rate from those in shear flow: after reaching a plateau value, (R(ete2)) and (R(g2)) are found to increase further as elongation rate increases. A minimum in the hydrostatic pressure is observed for hexadecane and tetracosane at about epsilon(msigma2/epsilon)1/2=0.02. This phenomenon is shown to be associated with the intermolecular LJ potential energy. The bond-bending and torsional energies display similar trends, but a different behavior is observed for the bond-stretching energy. An important observation common in these three bonded-intramolecular interactions is that all three modes are suppressed to a small value at high elongation rates. We conjecture that a liquid-crystal-like, nematic structure is present in these systems at high elongation rates, which is characterized by a strong chain alignment with a fully stretched conformation.

Transient uniaxial orientation of flexible polymer chains in a wide range of elongation rates

Affine evolution of chain end-to-end vectors distribution function is derived analytically for non-linear polymer liquids subjected to uniaxial elongational flow, controlled by time-evolution of chain deformation coefficients. Peterlin approximation for non-Gaussian chain elasticity is applied, with Padè approximation for the inverse Langevin function. The approach enables calculations of transient molecular deformation coefficients in entire range of elongation rates and times.Equations controlling time evolution of the molecular deformation coefficients in elongational flow are solved analytically with an assumption of dominating elongational component. The approach allows to decouple evolution equations and obtain an approximate closed form analytical formula describing time evolution of the molecular deformation with high accuracy, in particular at higher elongation rates, above the Gaussian limit.Predictions of the analytical formula are compared with numerical computations to evaluate the approximation and ranges of its validity.The analytical formula enables predicting evolution of average functions in non-linear systems, such as free energy, tensile stress, molecular orientation, etc. The formula is used to discuss molecular vs. macroscopic deformation in wide range of elongation rates and times, as well as evolution of stress, axial orientation factor, apparent elongational viscosity.

Viscosity overshoot in the start-up of uniaxial elongation of low density polyethylene melts

The transient uniaxial elongational viscosity of BASF Lupolen 1840D and 3020D melts has been measured on a filament stretch rheometer up to Hencky strains of 6–7. The elongational viscosity of both melts was measured at 130°C within a broad range of elongational rates. At high elongation rates, an overshoot or maximum in the transient elongational viscosity followed by a steady viscosity was observed. The steady elongation viscosity was about 40%–50% less than the maximum at high strain rates. The steady elongational viscosity as a function of the elongation rate, ϵ̇, decreases approximately as ϵ̇−0.6 in both melts at high strain rates. The transient elongational viscosity, measured at a specific elongation rate at 170°C on the BASF Lupolen 3020D melt, did not follow the time temperature superposition principle based on linear viscoelasticity during the decrease in the transient elongational viscosity towards the steady state.

Efeitos da adubação nitrogenada e de sistemas de manejo sobre a morfogênese de Lolium multiflorum Lam. e Paspalum urvillei Steud. em ambiente de várzea

Objetivou-se, com este experimento, avaliar a resposta morfogênica de Lolium multiflorum Lam. e Paspalum urvillei Steud., submetidos a níveis de adubação nitrogenada (100, 200 e 300 kg/ha de N). Os novilhos mantidos nesta pastagem recebiam diferentes níveis de suplementação energética (0,0; 0,4 e 0,8% do peso vivo), respectivamente, para os tratamentos de adubação. Adotou-se delineamento inteiramente casualizado, sendo avaliados 90 afilhos por tratamento, 45 de cada espécie por repetição. Foram utilizados afilhos marcados para avaliar as taxas de alongamento, aparecimento e desfolha e o filocrono de lâminas foliares das espécies. A suplementação propiciou efeito substitutivo para L. multiflorum, com menores taxas de desfolha no tratamento 300 kg/ha de N + 0,8% PV. Em P. urvillei, a taxa de desfolha foi elevada, independentemente de sua contribuição na massa de forragem. As maiores taxas de alongamento de L. multiflorum foram observadas com o uso de 300 kg/ha de N, o que induz à aplicação de maiores doses de N nos estádios iniciais. No período inicial, registrou-se a maior taxa de aparecimento de folhas no tratamento 100 kg/ha de N, com 12,5 dias para o aparecimento de nova folha. No segundo período, foram semelhantes e, no terceiro, o tratamento com 200 kg/ha de N apresentou a maior taxa, sendo necessários, em média, 14,1 dias para surgir nova folha. Com a aproximação do final do ciclo da espécie, a taxa de aparecimento diminuiu. A adubação nitrogenada não interfere no filocrono de ambas as espécies. A taxa de alongamento foliar de P. urvillei no tratamento com 300 kg/ha de N foi superior ao menor nível de N, em todos os períodos. A taxa média de aparecimento de folhas de P. urvillei foi de 0,07 folhas/dia. O intervalo médio para o aparecimento de nova folha foi de 14,1 dias, sendo influenciada principalmente pela soma térmica acumulada.

Phenotypic plasticity of an invasive acacia versus two native Mediterranean species.

The phenotypic plasticity and the competitive ability of the invasive Acacia longifolia v. the indigenous Mediterranean dune species Halimium halimifolium and Pinus pinea were evaluated. In particular, we explored the hypothesis that phenotypic plasticity in response to biotic and abiotic factors explains the observed differences in competitiveness between invasive and native species. The seedlings' ability to exploit different resource availabilities was examined in a two factorial experimental design of light and nutrient treatments by analysing 20 physiological and morphological traits. Competitiveness was tested using an additive experimental design in combination with 15N-labelling experiments. Light and nutrient availability had only minor effects on most physiological traits and differences between species were not significant. Plasticity in response to changes in resource availability occurred in morphological and allocation traits, revealing A. longifolia to be a species of intermediate responsiveness. The major competitive advantage of A. longifolia was its constitutively high shoot elongation rate at most resource treatments and its effective nutrient acquisition. Further, A. longifolia was found to be highly tolerant against competition from native species. In contrast to common expectations, the competition experiment indicated that A. longifolia expressed a constant allocation pattern and a phenotypic plasticity similar to that of the native species.

Population age structure and rhizome growth of Cymodocea nodosa in the Ria Formosa (southern Portugal)

The population age structure and derived population dynamics (recruitment, growth and mortality), rhizome growth and flowering effort of Cymodocea nodosa in the Ria Formosa (south of Portugal) were examined using reconstruction techniques. The horizontal rhizome elongation rates were low (13.8–30.7 cm year−1), which is consistent with the low population growth rate (−2.35 to 0.29 year−1). The vertical elongation rate was proportional to the horizontal growth except for one stand that was subjected to sand movements and had higher elongation rates. The mean leaf production varied from 11.8 to 14 leaves year−1. The average shoot age varied from 0.70 to 1.04 years, and the oldest shoot found was 7.6 years. The mortality rates were the highest as yet reported for this species (0.99–3.70 year−1). Observed low growth and high mortality are possibly associated with the development of eutrophic conditions in the Ria Formosa. The flowering probability found in Ria Formosa stands (<0.009–0.90 shoots−1 year−1) was comparable to that found in the Mediterranean and off the Canary Islands. Only two stands with flowering events were found inthe Ria Formosa population, which indicates that the stands are highly dependent on clonal growth to maintain themselves inthe Ria Formosa.

Simple constitutive models for linear and branched polymers

It is shown that several (single-mode) models (PTT, XPP) are basically special cases of the general network model. The XPP model [J. Rheol. 45 (2001) 823] is shown to give an identical response to a PTT model at high elongational rates, but the models differ in shear flow at high shear rates. The Giesekus term in the XPP model has practically no effect at any deformation rate except the generation of a second normal stress difference at small shear rates. The possibility of tailoring the shear flow response at high shear rates is explored. The results for the models are also given to show the effect of branching on the response in both transient and steady flows—elongation, shear, planar elongation and biaxial deformation. Finally, the fitting of data with multi-mode models is investigated.

Expression of a peroxidase gene in zucchini in relation with hypocotyl growth

The expression of the gene encoding an anionic isoperoxidase from zucchini ( Cucurbita pepo L., cv. Black Beauty) ( APRX) has been analyzed by northern blot, in situ hybridization and isoelectric focusing (IEF). Hypocotyls and stems were the organs containing the highest amount of APRX transcripts. A detailed study of APRX expression in hypocotyls revealed that the mRNA accumulated mainly beneath the apical hook, in the outer half of the hook and in the root tip, three zones characterized by a relatively high elongation rate. Seedlings grown in darkness or under a 12-h photoperiod exhibited a maximum APRX expression 5 or 6 d after germination, preceding an acceleration of hypocotyl growth. The seedlings grown under continuous light had a shorter hypocotyl and a lower level of expression. Surprisingly, the variations of APRX transcript level observed in the different hypocotyl zones or in hypocotyls of different ages did not result in visible changes in the amounts of APRX activity, as determined after IEF separation. The distribution of lignin along the hypocotyl and in the hook was inversely related to the level of APRX transcript.

Rupture of entangled polymeric liquids in elongational flow

Polymer melts and concentrated solutions rupture at high rates of elongation in a manner that is reminiscent of the cohesive failure of solids. We propose a simple molecular picture of rupture of a polymer filament, in which catastrophic failure occurs when the frictional force on an entangled chain can no longer balance the tension in the chain. The model, which is fully predictive and contains no adjustable parameters, captures the rupture characteristics of the available data sets and agrees quantitatively with critical stress–critical strain data and the dependence of critical strain on the Weissenberg number.

Gene cloning and function analysis of replication factor C from Thermococcus kodakaraensis KOD1.

Replication factor C (RFC) catalyzes the assembly of circular proliferating cell nuclear antigen (PCNA) clamps around primed DNA, enabling processive synthesis by DNA polymerase. The RFC-like genes, arranged in tandem in the Thermococcus kodakaraensis KOD1 genome, were cloned individually and co-expressed in Escherichia coli cells. T. kodakaraensis KOD1 RFC homologue (Tk-RFC) consists of the small subunit (Tk-RFCS: MW=37.2 kDa) and the large subunit (Tk-RFCL: MW=57.2 kDa). The DNA elongation rate of the family B DNA polymerase from T. kodakaraensis KOD1 (KOD DNA polymerase), which has the highest elongation rate in all thermostable DNA polymerases, was increased about 1.7 times, when T. kodakaraensis KOD1 PCNA (Tk-PCNA) and the Tk-RFC at the equal molar ratio of KOD DNA polymerase were reacted with primed DNA.

Crystal structure of DNA polymerase from hyperthermophilic archaeon Pyrococcus kodakaraensis KOD1

The crystal structure of family B DNA polymerase from the hyperthermophilic archaeon Pyrococcus kodakaraensis KOD1 (KOD DNA polymerase) was determined. KOD DNA polymerase exhibits the highest known extension rate, processivity and fidelity. We carried out the structural analysis of KOD DNA polymerase in order to clarify the mechanisms of those enzymatic features. Structural comparison of DNA polymerases from hyperthermophilic archaea highlighted the conformational difference in Thumb domains. The Thumb domain of KOD DNA polymerase shows an “opened” conformation. The fingers subdomain possessed many basic residues at the side of the polymerase active site. The residues are considered to be accessible to the incoming dNTP by electrostatic interaction. A β-hairpin motif (residues 242–249) extends from the Exonuclease (Exo) domain as seen in the editing complex of the RB69 DNA polymerase from bacteriophage RB69. Many arginine residues are located at the forked-point (the junction of the template-binding and editing clefts) of KOD DNA polymerase, suggesting that the basic environment is suitable for partitioning of the primer and template DNA duplex and for stabilizing the partially melted DNA structure in the high-temperature environments. The stabilization of the melted DNA structure at the forked-point may be correlated with the high PCR performance of KOD DNA polymerase, which is due to low error rate, high elongation rate and processivity.

Water relations and leaf expansion: importance of time scale.

The role of leaf water relations in controlling cell expansion in leaves of water-stressed maize and barley depends on time scale. Sudden changes in leaf water status, induced by sudden changes in humidity, light and soil salinity, greatly affect leaf elongation rate, but often only transiently. With sufficiently large changes in salinity, leaf elongation rates are persistently reduced. When plants are kept fully turgid throughout such sudden environmental changes, by placing their roots in a pressure chamber and raising the pressure so that the leaf xylem sap is maintained at atmospheric pressure, both the transient and persistent changes in leaf elongation rate disappear. All these responses show that water relations are responsible for the sudden changes in leaf elongation rate resulting from sudden changes in water stress and putative root signals play no part. However, at a time scale of days, pressurization fails to maintain high rates of leaf elongation of plants in either saline or drying soil, indicating that root signals are overriding water relations effects. In both saline and drying soil, pressurization does raise the growth rate during the light period, but a subsequent decrease during the dark results in no net effect on leaf growth over a 24 h period. When transpirational demand is very high, however, growth-promoting effects of pressurization during the light period outweigh any reductions in the dark, resulting in a net increase in growth of pressurized plants over 24 h. Thus leaf water status can limit leaf expansion rates during periods of high transpiration despite the control exercised by hormonal effects on a 24 h basis.

耐震設計に用いるジオグリッドの引張強さに関する一考察

Generally, as for the design tensile strength of geogrid used as reinforcement material, tensile strength is decided considering creep characteristic. It is also known that the tensile characteristic of geogrid made of polymer material depends on the elongation rate showing large tensile strength under high elongation rate. On the other hand, some methods of evaluating the design tensile strength for a dynamic design are proposed by some organizations. However, those methods aren't yet standardized. Realistically in such reason, the design tensile strength for the static design is also used for the dynamic design. When thinking of the design strength of geogrid in case of dynamic loading, tensile characteristics after creep phenomenon occurs by static load are a problem. Its characteristics depend on static load to make creep phenomenon occur, continuing time, elongation rate which acts on geogrid in case of the earthquake and so on. In this research, the tensile characteristics of geogrid after a creep phenomenon by the static load are tested. The techniques of the data gathering and evaluation, which is the basis about the setting of dynamic design tensile strength, are considered.

Factors affectingin vitro shoot proliferation ofMyrtus communis L.: A comparison of adult and seedling material

Two stocks of shoots growingin vitro, obtained from either seedlings or adult plants, were used to study the effects of material origin, the number of previous subcultures on the establishment medium, the explant type, and the macronutrients on shoot multiplication and elongation inMyrtus communis L., always in the presence of 4.4. μM benzyladenine (BA). Shoot proliferation was influenced mainly by stock origin, with higher responses from the adult material than from the seedling material, and by the number of subcultures, with the largest rates of multiplication and elongation in the first subculture. In the first subculture, the adult material was characterized by high rates of shoot multiplication and shoot elongation, and some shoots were hyperhydric. On the other hand, in the first subculture the seedling material was characterized by lower rates of shoot multiplication and elongation, and some shoots were affected by apical necrosis. In the third and the fifth subcultures, shoot multiplication and elongation declined in both materials, and hyperhydricity or apical necrosis were never found, although higher multiplication and elongation were consistently found for the adult material. The influence of the studied sources of variation is discussed in relation to shoot multiplication and elongation.