Propagation Cycle Research Articles

Variability of the 3' terminal of the polymerase gene of Grapevine leafroll-associated virus 3 isolates from Vale do São Francisco, Brazil

Many viral diseases, including leafroll, which is of great economic importance, affect grapevines (Vitis spp.). A complex of eight viruses [Grapevine leafroll-associated virus (GLRaV) -1 to 8] is associated with this disease. The objective of this study was to compare the variability of the 3' terminal region of the polymerase gene of three isolates of GLRaV-3 (Grapevine leafroll-associated virus-3), from Submédio do Vale do Rio São Francisco (Petrolina-PE) with that of other isolates available at the GenBank, including an isolate from North America and another from Southern Brazil. The viral RNA was extracted from three infected ELISA reactive plants and a fragment of 340 bp was amplified, by RT-PCR, using primers that recognize that portion of the polymerase gene found between nucleotides 8267 and 8606. The three isolates from Vale do Rio São Francisco named Pet-1, Pet-2 and Pet-3, showed similarities ranging from 98% and 94%, respectively to the isolates from North America (AF037268) and Southern Brazilian (AF438411). Considering the whole genome, the main variation found was one amino acid change at position 2766 (F2766Y). These preliminary data indicate the existence of a natural variation among GLRaV-3 isolates from grapevines. This could be due to the vegetative propagation and long cycle of the plant, associated with the error-prone nature of RNA-dependent RNA polymerase.

Chaperoning prions: the cellular machinery for propagating an infectious protein?

Newly made polypeptide chains require the help of molecular chaperones not only to rapidly reach their final three-dimensional forms, but also to unfold and then correctly refold them back to their biologically active form should they misfold. Most prions are an unusual type of protein that can exist in one of two stable conformations, one of which leads to formation of an infectious alternatively folded form. Studies in Baker's yeast (Saccharomyces cerevisiae) have revealed that prions can exploit the molecular chaperone machinery in the cell in order to ensure stable propagation of the infectious, aggregation-prone form. The disaggregation of yeast prion aggregates by molecular chaperones generates forms of the prion protein that can seed the protein polymerisation that underlies the prion propagation cycle. In this article, we review what we have learnt about the role of molecular chaperones in yeast prion propagation, describe a model that can explain the role of various classes of molecular chaperones and their co-chaperones, and speculate on the possible involvement of chaperones in the propagation of mammalian prions.

Somaclonal Variation in Coreopsis grandiflora `Domino'

Coreopsis grandiflora (tickseed) regenerates readily from leaf segments allowing the possibility to exploit somaclonal variation as a means to develop novel phenotypes. We used true leaves from in vitro seedlings of Coreopsis grandiflora `Domino' grown on MS basal medium as explants in a series of experiments to evaluate the effect of media, leaf explant orientation, and genotype on shoot regeneration. Genotype accounted for most of the variation with two particular seedlings regenerating freely and eight others generally recalcitrant. From these two seedlings, designated E2 and H2, shoots were regenerated and acclimated to the greenhouse over a period of weeks. Once the plants had established (≈6 weeks after acclimatization) they were vernalized by moving them to a lighted bench (12-h photoperiod) in a walk-in cooler at 4 °C .On transfer back into the greenhouse, the plants flowered within a few weeks; 15 of 175 somaclones were selected based on distinct differences in flower orientation and appearance. The selected somaclones were propagated by division and transplanted to the field in May 2002 in a randomized complete-block design with three-plant plots and three replications, to determine if the novel characteristics persisted through an additional propagation cycle. In the field, plant height, leaf dimension, flowering, and flower dimensions were scored in June-July 2003. Significant differences were found between somaclones and the original E2 and H2 similarly propagated seedlings for desirable (more petals per flower, greater flowering, shorter plants), undesirable (less flowering, smaller flowers), and neutral (narrower leaves, taller plants) traits.

Flow cytometric studies of the host-regulated cell cycle in algae symbiotic with green paramecium.

Paramecium bursaria (green paramecium) possesses endosymbiotically growing chlorella-like green algae. An aposymbiotic cell line of P. bursaria (MBw-1) was prepared from the green MB-1 strain with the herbicide paraquat. The SA-2 clone of symbiotic algae was employed to reinfect MBw-1 cells and thus a regreened cell line (MBr-1) was obtained. The regreened paramecia were used to study the impact of the host's growth status on the life cycle of the symbiotic algae. Firstly, the relationship between the timing of algal propagation and the host cell division was investigated by counting the algal cells in single host cells during and after the host cell division and also in the stationary phase. Secondly, the changes in the endogenous chlorophyll level, DNA content, and cell size in the symbiotic algae were monitored by flow cytometry and fluorescence microscopy. The number of algae was shown to be doubled prior to or during the host cell division and the algal population in the two daughter cells is maintained at constant level until the host cell cycle reenters the cytokinesis, suggesting that algal propagation and cell cycle are dependent on the host's cell cycle. During the host's stationary growth, unicellular algal vegetatives with low chlorophyll content were dominant. In contrast, complexes of algal cells called sporangia (containing 1-4 autospores) were present in the logarithmically growing hosts, indicating that algal cell division leading to the formation of sporangia with multiple autospores is active in the dividing paramecia.

Coal Combustion By-product (CCB) Utilization in Turfgrass Sod Production

Coal combustion by-products (CCB) are produced nationwide, generating 108 Mg of waste annually. Though varied, the majority of CCB are crystalline alumino-silicate minerals. Both disposal costs of CCB and interest in alternative horticultural/agricultural production systems have increased recently. Field studies assessed the benefit of CCB and organic waste/product mixtures as supplemental soil/growth media for production of hybrid bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davy] sod. Growth media were applied at depths of 2 to 4 cm (200 to 400 m3·ha-1) and vegetatively established by sprigging. Cultural practices typical of commercial methods were employed over 99- or 114-day growth periods. Sod was monitored during these propagation cycles, then harvested, evaluated, and installed offsite in a typical lawn-establishment method. Results showed mixtures of CCB and biosolids as growth media increased yield of biomass, with both media and tissue having greater nutrient content than the control media. Volumetric water content of CCB-containing media significantly exceeded that of control media and soil included with a purchased bermudagrass sod. Once installed, sod grown on CCB-media did not differ in rooting strength from control or purchased sod. When applied as described, physicochemical characteristics of CCB-media are favorable and pose little environmental risk to soil or water resources.

Growing season and hydrogen peroxide effects on root induction and development in Olea europaea L. (cvs ‘Frantoio’ and ‘Gentile di Larino’) cuttings

Semi-hardwood cuttings of ‘Frantoio’ (high rooting ability) and ‘Gentile di Larino’ (low rooting ability) cultivars were obtained from 1-year-old olive shoots sampled in mid-August during the 2000 and 2001 growing season. Semi-hardwood cuttings were dipped in IBA 4000 ppm and H 2O 2 (0%-control or 3.5% w/v) solutions before rooting in greenhouse equipped with an automatic mist system. At 57 and 88 days after the beginning of rooting treatments cuttings were scored for the presence of callus, roots and roots number. In both cultivars and years, the IBA 4000+H 2O 2 treatment significantly modified rooting of cuttings at 57 days in comparison with IBA 4000 treatment. The positive effects of H 2O 2 on rooting were gradually smoothed after 88 days. At the end of the propagation cycle (88th days), cuttings treated with IBA 4000+H 2O 2 had significantly higher root number in comparison with those treated with IBA 4000 alone.

Mechanism of the Chain Termination of the Allylnickel(II)-Catalyzed Polymerization of 1,3-Butadiene. A Density Functional Investigation for the Cationic [NiII(RC3H4)(cis-C4H6)L]+ Active Catalyst

Alternative mechanisms of chain termination of the allylnickel(II)-catalyzed polymerization of 1,3-dienes have been investigated by employing a gradient-corrected DFT method: namely, (I) the hydrogen transfer mechanism and (II) the hydrogen elimination mechanism. Several conceivable pathways for each of these mechanisms have been scrutinized for the well-characterized trans-1,4 regulating cationic allylnickel(II) [NiII(η3-RC3H4)(cis-C4H6)L]+ active catalyst. The transfer of a hydrogen atom from the C4(butenyl) carbon of the growing polymer chain to the coordinated monomer, which starts with the butadiene π-complex, is suggested to be the favorable mechanism of chain termination. This process is found to preferably proceed in a concerted fashion outside of the immediate proximity of the nickel atom. On the other hand, the hydrogen elimination occurring from the monomer insertion product by hydrogen abstraction from the polymer chain (C4(butenyl) carbon) yielding initially an diene hydride species, is seen to be kinetically disfavored. Accordingly, hydrogen elimination represents a less likely channel for chain termination. The monomer π-complex is the crucial species of the entire polymerization reaction course, as it serves as the precursor for the critical monomer insertion and allylic anti−syn elementary steps of the chain propagation cycle, as well as for the favorable hydrogen transfer chain termination channel. The present study provides, for the first time, a theoretically well-founded insight into the mechanism of molecular weight regulation for the allylnickel(II)-catalyzed polymerization of 1,3-dienes.

Selectivity of peroxide‐initiated graft modification of ethylene copolymers

AbstractExperimental data on the kinetics and selectivity of peroxide‐initiated graft modification of ethylene copolymers with vinyltriethoxysilane (VTEOS) and maleic anhydride (MAn) are presented. Rate data for the VTEOS modification and crosslinking of poly(ethylene‐co‐vinyl acetate) demonstrate the controlling influence of peroxide decomposition rates. Analysis of the selectivity for grafting versus crosslinking showed considerable scope for optimization of VTEOS modifications through variation of monomer and peroxide loadings. However, the MAn system was found to be less amenable to optimization, most likely because of differences in the graft propagation cycle and radical termination preferences.

Syntheses of 3-substituted 2,3-dihydrobenzofuranes, 1,2-dihydronaphtho(2,1-b)furanes, and 2,3-dihydro-1H-indoles by tandem ring closure-S(RN)1 reactions.

3-Substituted 2,3-dihydrobenzofuranes (7a-c), 1,2-dihydronaphtho(2,1-b)furanes (10a-c), and N-substituted 2,3-dihydro-1H-indoles (8a-c, 9a,b) are obtained in very good yields by S(RN)1 photostimulated reactions in liquid ammonia from adequate haloaromatic compounds ortho-substituted with a suitable double bond (3a,b; 4a,b; 5a; 6a,b) and Me3Sn-, Ph2P-, and -CH2NO2 anions. The novelty of the work involves the versatile application of a 5-exo ring closure process during the propagation cycle of the S(RN)1 reaction; the alkyl radical intermediates formed react with the nucleophiles to afford the ring closure-substituted heterocycles. The factors governing the observed product distribution are discussed.

Propylene polymerization with a bisiminepyridine iron complex: activation with Ph 3C [B(C 6F 5) 4] and AlR 3; iron hydride species in the catalytic cycle

In this work, the complex 2,6-bis [1-(2-isopropyl-6-methylphenylimino)ethyl]-pyridineiron(II)dichloride was used for propylene polymerization. Activation with Ph 3C [B(C 6F 5) 4] and subsequent treatment with triisobutylaluminium or triethylaluminium generated a very active polymerization catalyst for propylene. The kinetics of this polymerization reaction were investigated with mass-flowmeters. Further we show propagation-time-profiles of this reaction. Depending on the nature of the aluminiumalkyl we are able to determine different aliphatic endgroups in the polymer using 13 C NMR spectroscopy. Addition of hydrogen to the polymerization leads to higher activities and allows us to formulate a complete catalytic reaction cycle containing an iron hydride species. This cycle comprises one starting cycle and two propagation cycles which can be controlled with the aluminiumtrialkyl-propylene ratio.

The nucleotide sequence of Shiga toxin (Stx) 2e-encoding phage phiP27 is not related to other Stx phage genomes, but the modular genetic structure is conserved.

In this study we determined the complete nucleotide sequence of Shiga toxin 2e-encoding bacteriophage phi P27, isolated from the Shiga toxin-producing Escherichia coli patient isolate 2771/97. phi P27 is integrated as a prophage in the chromosomal yecE gene. This integration generates identity segments of attL and attR sites with lengths of 11 nucleotides. The integrated prophage genome has a size of 42,575 bp. We identified 58 open reading frames (ORFs), each with a length of >150 nucleotides. The deduced proteins of 44 ORFs showed significant homologies to other proteins present in sequence databases, whereas 14 putative proteins did not. For 29 proteins, we could deduce a putative function. Most of these are related to the basic phage propagation cycle. The phi P27 genome represents a mosaic composed of genetic elements which are obviously derived from related and unrelated phages. We identified five short linker sequences of 22 to 151 bp in the phi P27 sequence which have also been detected in a couple of other lambdoid phages. These linkers are located between functional modules in the phage genome and are thought to play a role in genetic recombination. Although the overall DNA sequence of phi P27 is not highly related to other known phages, the data obtained demonstrate a typical lambdoid genome structure.

A comparison of hedging and repeated cutting cycles for propagating clones of Sitka spruce

Hedging and serial propagation are two options for providing plant material for the long‐term propagation of conifer clones. This study compared both options using eight half‐sibling clones of Sitka spruce which were propagated for 18 years. The four treatments were propagation from the original plant (ortet), hedges from cuttings (ramets) of the first and second propagation cycles, and serial propagation from ramets of the most recent propagation cycle. Both rooting success and performance in a field experiment were compared. The best overall rooting was obtained from serial propagation from the previous cycle; and the poorest rooting was from cuttings from the original ortet. Rooting success was generally good from 1978 to 1994 (up to 18 years from seed) for serial propagation, but only up to 11 years for hedges. There were some differences between clones for rooting success, but the results were not consistent. In the field, there were no consistent differences in survival or height growth between propagation treatments over time. There was no evidence of any decline in vigour after 6 years' growth in the field for treatments planted out between 1982 and 1992 (i.e. between 4 and 14 years of age). There were some differences in stem form shortly after planting, with cuttings from serial propagation being more upright. However, such differences did not persist, with all treatments showing an upright pattern of growth within a few years of planting. The propagation success is encouraging for a clonal forestry strategy with Sitka spruce. The best long‐term option may be to use hedges for bulk propagation and replace them regularly by serial propagation. The results are discussed in relation to current thinking about maturation effects on rooting and subsequent early growth of cuttings in conifers.

An unprecedented cation radical chain Diels–Alder polymerization leading to novel carbazole polymers

The polymerization of 3,6-bis( trans-1′-propenyl)- N-phenylcarbazole in the presence of tris(4-bromophenyl)aminium hexachloroantimonate ( 1 + ) leads to soluble, high molecular weight, thermally stable cycloaddition polymers containing carbazole units in the main polymer chain. The reaction appears to proceed via a highly efficient cation radical chain mechanism which circumvents the usual hole transfer step of the propagation cycle. This polymerization represents the first observation of direct cation radical Diels–Alder cycloaddition polymerization.

Biocontrol of ticks by entomopathogenic nematodes. Research update.

Entomopathogenic nematodes (EPNs) are lethal to ticks even though they do not use their normal propagation cycle within tick cadavers. The tick Boophilus annulatus was found to be far more susceptible to EPNs than Hyalomma excavatum, Rhipicephalus bursa, or Rhipicephalus sanguineus. Ticks seem to be less susceptible to nematodes when feeding on a host. Preimaginal tick stages were less susceptible to nematodes than adult ticks. The mortality rate of unfed females was highest, followed by unfed males, and engorged females. The virulence of nematodes to ticks varied greatly among different nematode strains. In most cases, the Heterorhabditis sp. strains were the most virulent strains tested in petri dishes. In buckets containing sandy soil sprayed with 50 nematodes/cm2 and engorged B. annulatus females, the LT50 of the ticks was less than five days. The addition of manure to soil or a manure extract to petri dishes reduced nematode virulence. Since ticks spend most of their life cycle in the upper humid layer of the ground, and many nematode strains share this same ecological niche, the use of EPNs for biocontrol of ticks appears promising.

Spectrally resolved analysis of fast tuning in single-mode pulses generated from mutually injection-seeded Fabry-Perot laser diodes

Electrically wavelength-tunable pulses are generated from two mutually injection-seeded Fabry-Perot laser diodes at 1 GHz. By investigating the spectral dynamics, we experimentally show that stable single-mode output can be obtained after four roundtrip propagation cycles in the external cavity. We also probe the dynamic change of the spectrum during the switching between two single-mode wavelengths. It is found that the steady states can be reached after six to seven roundtrip cycles.

Soil Fumigation and Runner Plant Production: A Synthesis of Four Years of Strawberry Nursery Field Trials

Strawberry (Fragaria ×ananassa L.) runner plant production during a 4-year period was compared on nursery soils treated with methyl bromide (MB) and chloropicrin (CP) mixtures (MB:CP) and three alternative soil treatments: CP, mixtures of 1,3-dichloropropene (Telone®) and CP (DP:CP), and no fumigation (NF). The effect of soil treatment on runner plant production for a single nursery propagation cycle was determined in all 4 years. In 2 years, runner production in a final propagation cycle was also determined as a function of soil treatment in previous cycles. A single propagation cycle in NF soil decreased runner production relative to all other treatments. Treatments with CP at rates of 140 to 191 kg·ha–1 generally decreased runner production significantly (P ≤ 0.05) in comparison with treatment with MB:CP; use of CP at rates ≥303 kg·ha–1 resulted in statistically equivalent runner production. In one trial, use of two DP:CP formulations (516 kg·ha–1 of a 7:3 DP:CP mixture, and 448 kg·ha–1 of a 3:7 DP:CP mixture) significantly reduced and did not affect runner production, respectively, relative to the use of MB:CP. Use of MB:CP in the previous propagation cycle also increased runner productivity in comparison with NF. Runner productivity of planting stock produced with 314 kg·ha–1 of CP did not differ statistically from that of stock produced with MB:CP, but productivity of planting stock on soil treated with 157 kg·ha–1 of CP was intermediate between that on NF and MB:CP-treated soil. Planting stock grown on nontreated soil in two previous propagation cycles produced 25% fewer runner plants than did similar stock grown on MB:CP-treated soil. Productivity of planting stock produced with CP at rates of 280 to 314 kg·ha–1 in two previous propagation cycles did not differ statistically from that of stock produced with MB:CP. Results of meta-analyses indicated that fumigation with MB:CP was more effective in increasing runner production than was CP or NF, regardless of the propagation cycle or rate of application. For mixtures of 1,3-dichloropropene and CP, nursery productivity was maximized by using at least 280 kg·ha–1 of CP.

Activity of Homogeneous Chromium(III)-Based Alkene Polymerization Catalysts: Lack of Importance of the Barrier to Ethylene Insertion

The barrier to ethylene insertion into the chromium−methyl bond in Cp(H2O)CrMe+ (1), Cp(THF)CrMe+ (2), Cp(imidazol-2-ylidene)CrMe+ (3), (H2NC2H4C5H4)CrMe+ (4), and (Me2NC2H4C5H4)CrMe+ (5) has been calculated using gradient-corrected density functional theory (DFT) and compared to experimentally recorded activity data for homogeneous Cr(III)-based polymerization catalysts. The lack of correlation between the two data sets shows that the observed differences in activity among these catalysts do not originate from a difference in the ability of the various Cp(donor)CrR+ complexes to instigate the bond-breaking and -forming phases of the Cossée−Arlman-type insertion step. Rather, the superior performance of the donor-substituted Cp−Cr catalysts is probably associated with the enforced proximity of the donor group to the metal, demonstrating the importance of the constant presence of the donor ligand in the inner coordination sphere of the chromium atom. For 5, insertion of a second ethylene molecule has also been investigated, and the results reflect that for the Cr(III)-based catalysts the insertion step does not represent a serious bottleneck in the propagation cycle, consistent with the observed high activities of the recently developed amino-substituted Cp−Cr catalysts.

Mechanistic Studies of the 1,4-Polymerization of Butadiene According to the π-Allyl-Insertion Mechanism. 3. Density Functional Study of the C−C Bond Formation Reaction in Cationic “Ligand-Free” (η3:η2-Heptadienyl)(η2-/η4-butadiene)nickel(II) Complexes [Ni(C7H11)(C4H6)]+

According to the π-allyl-insertion mechanism the entire catalytic cycle of 1,4-polymerization of butadiene has been theoretically studied by employing a gradient-corrected density functional method with the polybutadienylnickel(II) cation [Ni(η3:η2:η2-RC12H18]+ as the precatalyst. We have investigated competitive chain propagation cycles for generation of a cis-1,4- and trans-1,4-polymer, and also anti−syn isomerization. The calculations provide a clear insight into the stereoregulation mechanism of cis-1,4-polymerization. Chain propagation proceeds via educt-like trigonal-bipyramidal transition states with an almost identical free activation energy of 12.0 kcal/mol for both the cis-1,4- and the trans-1,4-pathway. The free activation barrier for anti−syn isomerization is 19.0 kcal/mol, which takes place via π → σ conversion of the butenyl group followed by rotation of the vinyl group around the C2−C3 single bond through a trigonal-bipyramidal transition state. Accordingly, the trans-1,4-generating cycle i...

063 Biological Basis for Noninfectious Bud-failure in Almond (Prunus dulcis)

Noninfectious bud-failure (BF) is a genetic disorder in almond, associated with nursery source selection. Previously (Kester, PASHS, 1968), the latent potential for BF (BFpot) was shown to be heritable but its phenotypic expression (BFexp) varied among individual seedlings of a populations as a function of age. Vegetative propagation perpetuates BFpot of individual propagules (Kester and Asay, JASHS, 1978b) but the subsequent age of BFexp within individual plants is a function of accumulated exposure to high summer temperature and growth (Kester and Asay, JASHS 1978a). A recent 7-year “somatic heritability” study of 12 commercial nursery sources (Kester et al., HortScience 1998abst) portrays the total range of variability of BFpot and BFexp within the entire `Carmel' almond clonal population and includes a pattern of BF increase in consecutive vegetative propagation cycles that mimics patterns produced by phase change (i.e., juvenile > mature) phenomena (Hartmann et al., 1997). Although phase change potential is heritable in seedling populations, phase change expression is not (Kester, HortScience 1983). Furthermore phase changes can be reversed under particular conditions during consecutive vegetative propagations (Hartmann et al., 1997). In contrast, evidence shows that BF produces permanent changes in genotype that are heritable and irreversable. High correlations exist between BFpot of individual source blocks, individual trees and individual budsticks and the age and severity of BFexp in progeny trees. The apparent continuous change in BFpot and BFexp within clones appears to be the pattern of expression of different populations of increasingly defective (?) somatic cells that result from consecutive sequences of change during annual cycles of growth and generations of vegetative propagation.

Influence of anodization on the fatigue life of WE43A-T6 magnesium

An experimental study was performed to evaluate the influence of the anodic Magoxid-Coat on the fatigue life of WE43A-T6 magnesium. Rotating-bending fatigue tests were performed under ambient lab-air conditions at various stress levels over the cycle range N {approximately} 10{sup 3} to 30 {times} 10{sup 6}. Comparisons between the S-N curves for bare specimens and specimens with three different anodic coating thicknesses were made. The results showed no apparent influence of anodic coating thickness on fatigue strength. A decrease in strength of 11 to 6% was observed for the coated specimens in the long-life regime (N > 10{sup 5} cycles), but no difference was observed in the low cycles regime (N < 10{sup 4}). Microscopic observations of the specimen sides after testing showed that nonfatal fatigue cracks were initiated at applied stress levels above approximately 100 MPa on both the bare and anodized specimens. The difference in fatigue performance between the bare and anodized specimens is considered in terms of the coating`s influence on the cycles to crack initiation and cycles expended in propagating the crack to specimen failure. The initiation cycles are influenced by the pores and inclusions on the anodic coating surface and the barrier layer at themore » metal-oxide interface. The propagation cycles are influenced by the multiplicity and location of initiation sites, which affect, in turn, crack growth and coalescence during the fatigue fracture process.« less