Eimeria tenella: parasite-specific incorporation of 3H-uracil as a quantitative measure of intracellular development

An assay has been developed using parasite-specific incorporation of 3H-uracil to assess the intracellular growth of Eimeria tenella in vitro. As shown by both scintillation counts and autoradiography, 3H-uracil was incorporated specifically into intracellular parasites from the onset of infection and continued throughout development of the first generation schizonts. Mature schizonts and first generation merozoites did not continue to incorporate additional 3H-uracil, indicating that RNA synthesis had halted in these stages. Based on these findings, a semi-automated microscale uracil incorporation assay was developed to determine parasite viability. This method should be useful for biochemical studies with intracellular parasites and for screening compounds for anticoccidial activity. The ease, rapidity, and quantitative nature of this assay contrasts favorably with standard morphometric approaches of determining parasite development. In addition, parallel studies using host cell incorporation of 3H-uridine have been introduced as a method of determining whether antiparasitic activity is direct or indirect in relation to effects on the host cell.     

Effects of wounding on cytokinin activity in cucumber cotyledons

Three known physiological responses to exogenous cytokinins were measured in wounded and nonwounded cotyledons from cucumber (Cucumis sativus L. cv Marketer) seedlings grown in darkness. Enhanced cell division, chlorophyll formation, and cotyledon expansion were detected in wounded cotyledons. The data suggest that wounding enhances endogenous cytokinin activity.     

Geographical Variation in Body Size and Sexual Size Dimorphism in an Australian Lizard,Boulenger's Skink (Morethia boulengeri)

Ecogeographical rules help explain spatial and temporal patterns in intraspecific body size. However, many of these rules, when applied to ectothermic organisms such as reptiles, are controversial and require further investigation. To explore factors that influence body size in reptiles, we performed a heuristic study to examine body size variation in an Australian lizard, Boulenger''s Skink Morethia boulengeri from agricultural landscapes in southern New South Wales, south-eastern Australia. We collected tissue and morphological data on 337 adult lizards across a broad elevation and climate gradient. We used a model-selection procedure to determine if environmental or ecological variables best explained body size variation. We explored the relationship between morphology and phylogenetic structure before modeling candidate variables from four broad domains: (1) geography (latitude, longitude and elevation), (2) climate (temperature and rainfall), (3) habitat (vegetation type, number of logs and ground cover attributes), and (4) management (land use and grazing history). Broad phylogenetic structure was evident, but on a scale larger than our study area. Lizards were sexually dimorphic, whereby females had longer snout-vent length than males, providing support for the fecundity selection hypothesis. Body size variation in M. boulengeri was correlated with temperature and rainfall, a pattern consistent with larger individuals occupying cooler and more productive parts of the landscape. Climate change forecasts, which predict warmer temperature and increased aridity, may result in reduced lizard biomass and decoupling of trophic interactions with potential implications for community organization and ecosystem function.     

Comparative Studies on Plastoquinones: V. Changes in Lipophilic Chloroplast Quinones during Development

Changes of lipophilic chloroplast quinones in corn, oats, peas, and Vicia faba are reported after 0, 4, 8, 12, 16, 20, 24, 48, 72, or 96 hours of exposure to light. There is a pronounced increase in plastoquinone A and chlorophyll levels and slight increase, in plastoquinone C_1-6, vitamin K₁, and α-tocopherylquinone content. Coenzyme Q levels, on the other hand, show little change upon exposure to light.     

Glandulocalyx upatoiensis, a fossil flower of Ericales (Actinidiaceae/Clethraceae) from the Late Cretaceous (Santonian) of Georgia, USA

Background and Aims

Ericales are a major group of extant asterid angiosperms that are well represented in the Late Cretaceous fossil record, mainly by flowers, fruits and seeds. Exceptionally well preserved fossil flowers, here described as Glandulocalyx upatoiensis gen. & sp. nov., from the Santonian of Georgia, USA, yield new detailed evidence of floral structure in one of these early members of Ericales and provide a secure basis for comparison with extant taxa.

Methods

The floral structure of several fossil specimens was studied by scanning electron microscopy (SEM), light microscopy of microtome thin sections and synchrotron-radiation X-ray tomographic microscopy (SRXTM). For direct comparisons with flowers of extant Ericales, selected floral features of Actinidiaceae and Clethraceae were studied with SEM.

Key Results

Flowers of G. upatoiensis have five sepals with quincuncial aestivation, five free petals with quincuncial aestivation, 20–28 stamens arranged in a single series, extrorse anther orientation in the bud, ventral anther attachment and a tricarpellate, syncarpous ovary with three free styles and numerous small ovules on axile, protruding-diffuse and pendant placentae. The calyx is characterized by a conspicuous indumentum of large, densely arranged, multicellular and possibly glandular trichomes.

Conclusions

Comparison with extant taxa provides clear evidence for a relationship with core Ericales comprised of the extant families Actinidiaceae, Roridulaceae, Sarraceniaceae, Clethraceae, Cyrillaceae and Ericaceae. Within this group, the most marked similarities are with extant Actinidiaceae and, to a lesser degree, with Clethraceae. More detailed analyses of the relationships of Glandulocalyx and other Ericales from the Late Cretaceous will require an improved understanding of the morphological features that diagnose particular extant groups defined on the basis of molecular data.     

Identification and characterization of a new family of high-affinity receptors for Escherichia coli heat-stable enterotoxin in rat intestinal membranes.

Novel high-affinity, low-capacity binding sites in intestinal membranes for the heat-stable toxin produced by Escherichia coli have been defined. The appearance of these sites is observed in the presence of physiological concentrations of NaCl in binding reactions. Scatchard analyses of equilibrium binding in the absence of NaCl demonstrated a single class of binding sites with KD = 1.9 x 10(-9) M and Bmax = 0.75 pmol/mg of protein. In contrast, similar experiments in the presence of NaCl demonstrated, in addition to the previously described low-affinity site, a high-affinity site with a KD of 2.1 x 10(-11) M and a Bmax of 73 fmol/mg of protein. Confirmation of the presence of high- and low-affinity sites was obtained in studies of the kinetics of ST binding. These sites exhibited similar dissociation but markedly different association kinetics. Determination of the association and dissociation constants permitted calculation of the KD's for the high- and low-affinity sites, which were 1.15 x 10(-11) M and 1.89 x 10(-9) M, respectively. These data agree closely with those obtained in studies of equilibrium binding. Furthermore, similar values for the KD's of these sites were obtained in experiments of competitive displacement of labeled ST, confirming the presence of two receptors for this toxin. Binding of ST to high-affinity sites is completely reversible and does not appear to be coupled to activation of particulate guanylate cyclase. In contrast, binding of ST to low-affinity sites appears to be partially reversible and may be coupled to activation of guanylate cyclase.(ABSTRACT TRUNCATED AT 250 WORDS)     

Inhibition of transplasma membrane electron transport by monoclonal antibodies to the transferrin receptor

Reduction of iron in diferric transferrin is inhibited by monoclonal antibodies to the transferrin receptor which bind at sites other than the high affinity transferrin binding site. These antibodies include B3/25, GB16 and GB22. Two antibodies which bind at the high affinity site for transferrin, 42/6 and GB18, do not inhibit iron reduction by transplasma membrane electron transport. The results are consistent with the proposal that differric transferrin reduction or stimulation of transmembrane NADH oxidase activity involves a site different from the high affinity diferric transferrin binding site. A synergistic action of antibodies with epitopes at the tight binding site involved in iron uptake and the antibodies which inhibit electron transport, B3/25 and GB16, can explain the increased inhibition of growth observed when both 42/6 and B3/25 are added to proliferating cells.