Routes of Ethephon Uptake in Pineapple (Ananas comosus) and Reasons for Failure of Flower Induction

Ethylene-releasing agents such as ethephon (2-chloroethylphosphonic acid) are used widely to induce flowering in pineapples (Ananas comosus (L.) Merrill). However, ethephon treatment is less reliable in summer, particularly if plants are treated on abnormally hot days. [¹⁴C]ethephon was used to follow uptake and translocation in leaf tissues. Up to 30% of the ethephon entered the leaf within 4 h, and up to 60% by 24 h. Uptake was dramatically modified by temperature, relative humidity, solution pH, and the surface on which solution droplets were placed. Entry occurred across the leaf cuticle and probably also by way of stomatal pores, and label was recovered at all depths within the leaf. ¹⁴C label entered more rapidly through the abaxial epidermis than through the adaxial epidermis. Low-volume spray applications to whole plants resulted in rapidly drying droplets mainly on the adaxial, distal epidermis and were rather ineffective at inducing flowering, possibly because little ethephon or ethylene reaches the shoot apex. High-volume sprays may facilitate ethephon entry because solution accumulates in leaf axils and hence remains in prolonged contact with abaxial epidermis of leaf bases close to the shoot apex. When poured into the center of the plant, 20% of a normal commercial ethephon dose induced full flowering even under adverse temperatures. It is suggested that high-volume evening spraying and avoidance of hot days may reduce the incidence of flowering failure. Received March 20, 1998; accepted September 6, 1999     

Two crystal structures demonstrate large conformational changes in the eukaryotic ribosomal translocase

Two crystal structures of yeast translation elongation factor 2 (eEF2) were determined: the apo form at 2.9 A resolution and eEF2 in the presence of the translocation inhibitor sordarin at 2.1 A resolution. The overall conformation of apo eEF2 is similar to that of its prokaryotic homolog elongation factor G (EF-G) in complex with GDP. Upon sordarin binding, the three tRNA-mimicking C-terminal domains undergo substantial conformational changes, while the three N-terminal domains containing the nucleotide-binding site form an almost rigid unit. The conformation of eEF2 in complex with sordarin is entirely different from known conformations observed in crystal structures of EF-G or from cryo-EM studies of EF-G-70S complexes. The domain rearrangements induced by sordarin binding and the highly ordered drug-binding site observed in the eEF2-sordarin structure provide a high-resolution structural basis for the mechanism of sordarin inhibition. The two structures also emphasize the dynamic nature of the ribosomal translocase.     

Spontaneously beating neonatal rat heart myocyte culture-a model to characterize angiotensin II at(1) receptor autoantibodies in patients with preeclampsia

This report focuses on angiotensin II AT(1) receptor autoantibodies (anti-AT(1)-AABs) in preeclamptic women. An enzyme-linked immunosorbent assay was described. Biotinylated peptide was incubated with anti-AT(1)-AABs. Streptavidin-coated magnetic particles bind the protein-autoantibody complex. Detection of anti-AT(1)-AABs was performed using anti-human IgG3 peroxidase-coupled antibody. The color reaction of tetramethylbenzidine solution was stopped by adding 0.5 M H(2)SO(4). Optical density was measured at 450 nm (620 nm reference filter). Seventy-nine percent of anti-AT(1)-AAB-positive patients (measured by bioassay) showed an increase in optical density (>145%). The same biotinylated peptide was successfully used for purification of 6/6 anti-AT(1)-AABs. Chronotropic effects of purified antibodies were registered on primary cultured neonatal rat cardiomyocytes with the computer imaging system IMAGOQUANT. Western blot of coimmunoprecipitation of angiotensin II AT(1) receptor shows one band (molecular weight >40.0 kDa) in potassium thiocyanate eluate.     

Herbivory and novel weapons: no evidence for enhanced competitive ability or allelopathy induction of <Emphasis Type="Italic">Centaurea diffusa</Emphasis> by biological controls

Biological control of weeds by arthropod herbivores is thought to work by reducing the competitive ability of the weed relative to the surrounding vegetation. However, the assumption that herbivory reduces plant competitive ability has not been tested in most biological control systems, and counter to expectation, recent research on the impact of biological control agents on invasive Centaurea species suggests that this genus may respond to herbivory by increased competitive ability through enhanced plant re-growth and/or by inducing increased production of phytotoxic allelochemicals. We examined the impact of two biological control agents of the invasive plant diffuse knapweed (C. diffusa) to see if feeding by either of these insects would enhance the plant’s competitive ability or allelochemical output. Sub-lethal herbivory by either of the biological control agents significantly reduced knapweed performance when the plant was grown in competition with either of two native species. Competition with knapweed significantly reduced the performance of both native species (Artemisia frigida and Bouteloua gracilis), and herbivory by one of the biocontrol agents resulted in a small but significant increase in both native species’ performance. Diffuse knapweed’s putative allelochemical 8-hydroxyquinoline was not detected in experimental or field collected soils from knapweed-infested sites. In contrast to other studies on the impacts of biological control on other Centaurea species, these data support the premise that biological control agents may reduce invading plant competitive ability. We find no evidence for diffuse knapweed allelopathy mediated by 8-hydroxyquinoline or enhanced allelopathy in response to herbivory by biological control agents.     

Genetic diversity of eleven European pig breeds

A set of eleven pig breeds originating from six European countries, and including a small sample of wild pigs, was chosen for this study of genetic diversity. Diversity was evaluated on the basis of 18 microsatellite markers typed over a total of 483 DNA samples collected. Average breed heterozygosity varied from 0.35 to 0.60. Genotypic frequencies generally agreed with Hardy-Weinberg expectations, apart from the German Landrace and Schwäbisch-Hällisches breeds, which showed significantly reduced heterozygosity. Breed differentiation was significant as shown by the high among-breed fixation index (overall F_ST = 0.27), and confirmed by the clustering based on the genetic distances between individuals, which grouped essentially all individuals in 11 clusters corresponding to the 11 breeds. The genetic distances between breeds were first used to construct phylogenetic trees. The trees indicated that a genetic drift model might explain the divergence of the two German breeds, but no reliable phylogeny could be inferred among the remaining breeds. The same distances were also used to measure the global diversity of the set of breeds considered, and to evaluate the marginal loss of diversity attached to each breed. In that respect, the French Basque breed appeared to be the most "unique" in the set considered. This study, which remains to be extended to a larger set of European breeds, indicates that using genetic distances between breeds of farm animals in a classical taxonomic approach may not give clear resolution, but points to their usefulness in a prospective evaluation of diversity.     

Bone marrow cell dose and kinetics of recovery following allogeneic marrow transplantation in man

In 50 patients transplanted for acute or chronic leukemia we studied the correlation between the number of infused bone marrow cells/kg recipient body weight and the time needed for engraftment. Engraftment was arbitrarily defined as the first day of 1 X 10(9) leukocytes/l and of 20 X 10(9) reticulocytes/l after the posttransplantation nadir. There is a negative non-linear correlation between the duration of leukopenia following marrow transplantation and the amount of transfused nucleated cells (p = 0.01). Since the incidence of infectious or hemorrhagic complications depends directly on the duration of aplasia it is justifiable to give a maximal cell dose.     

SuperSegger: robust image segmentation,analysis and lineage tracking of bacterial cells

Many quantitative cell biology questions require fast yet reliable automated image segmentation to identify and link cells from frame‐to‐frame, and characterize the cell morphology and fluorescence. We present SuperSegger, an automated MATLAB‐based image processing package well‐suited to quantitative analysis of high‐throughput live‐cell fluorescence microscopy of bacterial cells. SuperSegger incorporates machine‐learning algorithms to optimize cellular boundaries and automated error resolution to reliably link cells from frame‐to‐frame. Unlike existing packages, it can reliably segment microcolonies with many cells, facilitating the analysis of cell‐cycle dynamics in bacteria as well as cell‐contact mediated phenomena. This package has a range of built‐in capabilities for characterizing bacterial cells, including the identification of cell division events, mother, daughter and neighbouring cells, and computing statistics on cellular fluorescence, the location and intensity of fluorescent foci. SuperSegger provides a variety of postprocessing data visualization tools for single cell and population level analysis, such as histograms, kymographs, frame mosaics, movies and consensus images. Finally, we demonstrate the power of the package by analyzing lag phase growth with single cell resolution.     

Traction force on a kinetochore at metaphase acts as a linear function of kinetochore fiber length

We are investigating the relation between the force pulling a kinetochore poleward and the length of the corresponding kinetochore fiber. It was recognized by Ostergren in 1950 (Hereditas 36:1-19) that the metaphase position of a chromosome could be achieved by a balance of traction forces were proportional to the distance from kinetochore to pole. For the typical chromosome (i.e., a meiotic bivalent or mitotic chromosome) with a single kinetochore fiber extending to each pole, the resultant force (RF) would equal zero when the chromosome lay at the midpoint between the two poles. For special chromosomes that have unequal numbers of kinetochore fibers extending towards opposite poles. For special chromosomes that have unequal numbers of kinetochore fibers extending towards opposite poles. For special chromosomes that have unequal numbers of kinetochore fibers extending towards opposite poles, Ostergren’s proposal suggests that RF = 0 when the chromosome is shifted closer to the pole toward which the greater number of kinetochore fibers are pulling. We have measured the force-length relationship in living spindles by analyzing the metaphase positions of experimentally generated multivalent chromosomes having three or four kinetochore fibers. Multivalent chromosomes of varied configurations were generated by γ-irradiation of nymphs of the grasshopper melanoplus differentialis, and their behavior was analyzed in living first meiotic spermocytes. The lengths of kinetochore fibers were determined from time-lapse photographs by measuring the kinetochore-to-pole distances for fully congressed chromosomes just before the onset of anaphase. In our analysis, force (F) along a single kinetochore fiber is expressed by: F = kL(exp), where k is a length-independent proportionality constant, L represents the kinetochore fiber length, and exp is an unknown exponent. The RF on a chromosome is then given by: RF = σk(i)L(i)(exp), where kinetochore fiber lengths in opposite half- spindles are given opposite sign. If forces on a metaphase chromosome are at equilibrium (RF = 0), then for asymmetrical orientations of multivalents we can measure the individual kinetochore fiber lengths (L(i)) and solve for the exponent that yields a resultant force of zero. The value of the exponent relates how the magnitude of force along a kinetochore fiber varies with its length. For six trivalents and one naturally occurring quadrivalent we calculated an average value of exp = 1.06 +/- 0.18. This result is consistent with Ostergren’s hypothesis and indicates that the magnitude of poleward traction force along a kinetochore fiber is directly proportional to the length of the fiber. Our finding suggests that the balance of forces along a kinetochore fiber may be a major factor regulating the extent of kinetochore microtubule assembly.     

Colitis-inducing potency of CD4+ T cells in immunodeficient, adoptive hosts depends on their state of activation, IL-12 responsiveness, and CD45RB surface phenotype

We studied the induction, severity and rate of progression of inflammatory bowel disease (IBD) induced in SCID mice by the adoptive transfer of low numbers of the following purified BALB/c CD4+ T cell subsets: 1) unfractionated, peripheral, small (resting), or large (activated) CD4+ T cells; 2) fractionated, peripheral, small, or large, CD45RBhigh or CD45RBlow CD4+ T cells; and 3) peripheral IL-12-unresponsive CD4+ T cells from STAT-4-deficient mice. The adoptive transfer into SCID host of comparable numbers of CD4+ T cells was used to assess the colitis-inducing potency of these subsets. Small CD45RBhigh CD4+ T lymphocytes and activated CD4+ T blasts induced early (6-12 wk posttransfer) and severe disease, while small resting and unfractionated CD4+ T cells or CD45RBlow T lymphocytes induced a late-onset disease 12-16 wk posttransfer. SCID mice transplanted with STAT-4-/- CD4+ T cells showed a late-onset IBD manifest > 20 wk posttransfer. In SCID mice with IBD transplanted with IL-12-responsive CD4+ T cells, the colonic lamina propria CD4+ T cells showed a mucosa-seeking memory/effector CD45RBlow Th1 phenotype abundantly producing IFN-gamma and TNF-alpha. In SCID mice transplanted with IL-12-unresponsive STAT-4-/- CD4+ T cells, the colonic lamina propria, mesenteric lymph node, and splenic CD4+ T cells produced very little IFN-gamma but abundant levels of TNF-alpha. The histopathologic appearance of colitis in all transplanted SCID mice was similar. These data indicate that CD45RBhigh and CD45RBlow, IL-12-responsive and IL-12-unresponsive CD4+ T lymphocytes and lymphoblasts have IBD-inducing potential though of varying potency.