Preliminary evaluation of non-native rainbow trout (Oncorhynchus mykiss) impact on the Cederberg ghost frog (Heleophryne depressa) in South Africa’s Cape Fold Ecoregion

We evaluated the impact of non-native rainbow trout Oncorhynchus mykiss on a population of endemic Cedarberg ghost frog Heleophryne depressa in the upper Krom River (Olifants-Doring River Catchment, Cape Fold Ecoregion). We compared H. depressa abundance (using kick-sampling and underwater video analysis) and environmental conditions between sites above and below a waterfall that marks the upper distribution limit of O. mykiss. Heleophryne depressa abundance was significantly greater above the waterfall than that below it, and, because there was no significant difference in measured environmental variables, O. mykiss presence is identified as the most likely explanation for the observed decrease in H. depressa abundance.     

Attraction of a kleptoparasitic sphaerocerid fly (Norrbomia frigipennis) to dung beetles (Phanaeus spp. andCanthon sp.)

Norrbomia frigipennis (Diptera: Sphaeroceridae) is phoretic on dung-feeding scarab beetles (Coleoptera: Scarabaeidae). In this study we investigate the attractiveness of three beetle species,Phanaeus ignius, P. vindex, andCanthon pilularis, to the fly. Stationary, moving-dead, and live beetles were used. More flies were attracted toPhanaeus. However, this attractiveness may be due to the larger average size ofPhanaeus. A preference for larger individuals was found withinPhanaeus, though not withinC. pilularis. Flies mounted beetles on the thorax and the elytra at similar rates.Phanaeus males that possesed horns did not attract more flies than did hornless ones, and there was no effect of host sex on attractiveness. In hornedPhanaeus, about 11–16% of the flies mounting those beetles landed on the horn.     

Biocontrol of Mold Growth in High-Moisture Wheat Stored under Airtight Conditions by Pichia anomala, Pichia guilliermondii, and Saccharomyces cerevisiae

Volume 61, no. 3, p. 1029, Table 1, boxhead over columns 2 to 4: "(CFU/plate)" should read "(log CFU/plate)." FIG. 1 [This corrects the article on p. 1027 in vol. 61.].     

Insertion of leader peptidase into the thylakoid membrane during synthesis in a chloroplast translation system

The mechanisms of targeting and insertion of chloroplast-encoded thylakoid membrane proteins are poorly understood. In this study, we have used a translation system isolated from chloroplasts to begin to investigate these mechanisms. The bacterial membrane protein leader peptidase (Lep) was used as a model protein because its targeting and insertion mechanisms are well understood for Escherichia coli and for the endoplasmic reticulum. Lep could thus provide insight into the functional homologies between the different membrane systems. Lep was efficiently expressed in the chloroplast translation system, and the protein could be inserted into thylakoid membranes with the same topology as in E. coli cytoplasmic membranes, following the positive-inside rule. Insertion of Lep into the thylakoid membrane was stimulated by the trans-thylakoid proton gradient and was strongly inhibited by azide, suggesting a requirement for SecA activity. Insertion most likely occurred in a cotranslational manner, because insertion could only be observed if thylakoid membranes were present during translation reactions but not when thylakoid membranes were added after translation reactions were terminated. To halt the elongation process at different stages, we translated truncated Lep mRNAs without a stop codon, resulting in the formation of stable ribosome nascent chain complexes. These complexes showed a strong, salt-resistant affinity for the thylakoid membrane, implying a functional interaction of the ribosome with the membrane and supporting a cotranslational insertion mechanism for Lep. Our study supports a functional homology for the insertion of Lep into the thylakoid membrane and the E. coli cytoplasmic membrane.     

Cell-to-cell and phloem-mediated transport of potato virus X. The role of virions

Movement-deficient potato virus X (PVX) mutants tagged with the green fluorescent protein were used to investigate the role of the coat protein (CP) and triple gene block (TGB) proteins in virus movement. Mutants lacking either a functional CP or TGB were restricted to single epidermal cells. Microinjection of dextran probes into cells infected with the mutants showed that an increase in the plasmodesmal size exclusion limit was dependent on one or more of the TGB proteins and was independent of CP. Fluorescently labeled CP that was injected into epidermal cells was confined to the injected cells, showing that the CP lacks an intrinsic transport function. In additional experiments, transgenic plants expressing the PVX CP were used as rootstocks and grafted with nontransformed scions. Inoculation of the PVX CP mutants to the transgenic rootstocks resulted in cell-to-cell and systemic movement within the transgenic tissue. Translocation of the CP mutants into sink leaves of the nontransgenic scions was also observed, but infection was restricted to cells close to major veins. These results indicate that the PVX CP is transported through the phloem, unloads into the vascular tissue, and subsequently is transported between cells during the course of infection. Evidence is presented that PVX uses a novel strategy for cell-to-cell movement involving the transport of filamentous virions through plasmodesmata.     

The movement protein of cucumber mosaic virus traffics into sieve elements in minor veins of nicotiana clevelandii

The location of the 3a movement protein (MP) of cucumber mosaic virus (CMV) was studied by quantitative immunogold labeling of the wild-type 3a MP in leaves of Nicotiana clevelandii infected by CMV as well as by using a 3a-green fluorescent protein (GFP) fusion expressed from a potato virus X (PVX) vector. Whether expressed from CMV or PVX, the 3a MP targeted plasmodesmata and accumulated in the central cavity of the pore. Within minor veins, the most extensively labeled plasmodesmata were those connecting sieve elements and companion cells. In addition to targeting plasmodesmata, the 3a MP accumulated in the parietal layer of mature sieve elements. Confocal imaging of cells expressing the 3a-GFP fusion protein showed that the 3a MP assembled into elaborate fibrillar formations in the sieve element parietal layer. The ability of 3a-GFP, expressed from PVX rather than CMV, to enter sieve elements demonstrates that neither the CMV RNA nor the CMV coat protein is required for trafficking of the 3a MP into sieve elements. CMV virions were not detected in plasmodesmata from CMV-infected tissue, although large CMV aggregates were often found in the parietal layer of sieve elements and were usually surrounded by 3a MP. These data suggest that CMV traffics into minor vein sieve elements as a ribonucleoprotein complex that contains the viral RNA, coat protein, and 3a MP, with subsequent viral assembly occurring in the sieve element parietal layer.     

The cell types in the endocrine pancreas of the human fetus

Summary Morphological and histochemical studies of the developing human islet cells are facilitated by the characteristic localization of the different islet cell types from about the third intrauterine month. By combining light microscopical analyses of silver impregnated and granule stained pancreatic sections with electron microscopy of osmium fixed material, the following four types of islet cells could be identified: (1) A₁ cells containing faint globular granules. These granules could be visualized only with the electron microscope. (2) A₂ cells containing electron-dense globular granules. It is uncertain whether the observation of a light and a dark variety of the A₂ cells reflects different stages of maturation or signifies cells with different secretion products. (3) B cells with irregular granules, which were often accumulated at the capillary pole of the cells. (4) Agranular islet cells. Mixed forms of A cells containing both faint and dense granules were also encountered. The difficulties in evaluating in the light microscope what may be called D cells in the human fetal islets were obvious from the observation of more cells stained with light-green than A₁ cells. Except for acid phosphatases, the histochemical tests for different phosphatases and esterases revealed rather weak or negative reactions in the islet cells. The development of phosphatase and esterase activities in the islets seemed far from complete, when morphologically differentiated islet cells could be recognized.Supported by the United States Public Health Service [grants RF-83(01) and TW-83(02)] and the Swedish Medical Research Council. The authors are indebted to Professor Carl Gemzell and Dr. Ulf Elvkull at the Department of Obstetrics and Gynecology, University Hospital, Uppsala, for the generous supply of the fetal pancreatic material.     

The dry mass of the pancreatic B-cells in relation to their content of secretion granules

Synopsis The dry mass of single islet cells was determined in obese-hyperglycemic mice. In one group of animals intense degranulation of the islet cells was brought about by adding glucose to the drinking water and by injections of anti-insulin serum. When the B-cell dry mass of these animals, (1.56±0.05)10^–10 g, was compared with that of corresponding cells from starved animals (1.83±0.04)10^–10 g, the latter value was found to be significantly higher. The observed difference (about 15%) agrees with that given in previous reports on the percentage of insulin in lyophilised B-cells.     

First fungus gnats of genus Manota Williston (Diptera: Mycetophilidae) from Japan

The genus Manota is recorded from Japan for the first time. Three new species, Manota satoyamanis, Manota indahae and Manota tunoae spp. nov., are described, based on specimens collected in an ecological sampling program of arthropods in the “satoyama” landscape of Ishikawa Prefecture. “Satoyama” represents the traditional rural landscape of Japan, which is characterized by a mosaic of secondary forests, plantations, ponds and rice paddy fields. The new species raise the number of Palearctic Manota species from five to eight.     

An Auxin Gradient and Maximum in the Arabidopsis Root Apex Shown by High-Resolution Cell-Specific Analysis of IAA Distribution and Synthesis

Local concentration gradients of the plant growth regulator auxin (indole-3-acetic acid [IAA]) are thought to instruct the positioning of organ primordia and stem cell niches and to direct cell division, expansion, and differentiation. High-resolution measurements of endogenous IAA concentrations in support of the gradient hypothesis are required to substantiate this hypothesis. Here, we introduce fluorescence-activated cell sorting of green fluorescent protein–marked cell types combined with highly sensitive mass spectrometry methods as a novel means for analyses of IAA distribution and metabolism at cellular resolution. Our results reveal the presence of IAA concentration gradients within the Arabidopsis thaliana root tip with a distinct maximum in the organizing quiescent center of the root apex. We also demonstrate that the root apex provides an important source of IAA and that cells of all types display a high synthesis capacity, suggesting a substantial contribution of local biosynthesis to auxin homeostasis in the root tip. Our results indicate that local biosynthesis and polar transport combine to produce auxin gradients and maxima in the root tip.