Electron microprobe analysis of intracellular electrolytes in resting and isoproterenol-stimulated exocrine glands of frog skin

Summary In the intact, in vitro frog skin, isoproterenol (ISO) stimulates and amiloride-insensitive increase in short-circuit current (SCC) that can be localized to the exocrine glands and is associated with secretion of chloride. To determine which cells in the glands respond to stimulation we measured the intracellular electrolyte concentrations of the various cell types of the mucous and seromucous glands of the skin using freeze-dried cryosections and electron microprobe analysis. In the resting state, the various cell types of the glands have intracellular electrolyte concentrations similar to the epithelial cells of the skin. Exposure to amiloride (10^–4 m) has little effect on the concentration of Na and Cl in the cells of the glands. The effect of isoproterenol has two distinct phases. Analysis of glands in tissues frozen at the peak of the SCC response (13 min after addition of isoproterenol) shows that the only significant change is an increase in Na and Ca in a group of cells at the ductal pole of the acini of both gland types. These are termed gland cells. The duct cells and cells that secrete macromolecules did not show any significant changes at this timepoint. In the gland cells, after a one-hour exposure to isoproterenol the Na concentration is at prestimulation levels while Cl drops. There is also a smaller drop in Cl in the duct and skin epithelial cells. Ouabain, which can completely block the isoproterenol SCC response, has little short-term effect on Na and Cl in the control gland but accentuates the gain of Na and drop in Cl in the isoproterenol-treated condition. Bumetanide and, to a lesser extent, furosemide, also blocks the isoproterenol SCC response and causes a further drop in Cl. The results provide indirect evidence that a major portion of the ionic component of the gland secretion is produced by a distinct group of cells separate from those producing the macromolecular component and that the mechanism of secretion involves a Na:Cl coupled transport system linked to the activity of the basolateral Na pump.     

The mechanistic nature of the membrane potential dependence of sodium-sugar cotransport in small intestine

Summary Methods are described which demonstrate the use of unidirectional influx of¹⁴C-tetraphenylphosphonium (¹⁴C-TPP⁺) into isolated intestinal epithelial cells as a quantitative sensor of the magnitude of membrane potentials created by experimentally imposed ion gradients. Using this technique the quantitative relationship between membrane potential () and Na⁺-dependent sugar influx was determined for these cells at various Na⁺ and -methylglucoside (-MG) concentrations. The results show a high degree of dependence for the transport Michaelis constant but a maximum velocity for transport which is independent of . No transinhibition by intracellular sugar (40mm) can be detected. Sugar influx in the absence of Na⁺ is insensitive to 1.3mm phlorizin and independent of . The mechanistic implications of these results were evaluated using the quality of fit between calculated and experimentally observed kinetic constants for rate equations derived from several transport models. The analysis shows that for models in which translocation is the potential-dependent step the free carrier cannot be neutral. If it is anionic, the transporter must be functionally asymmetric. A model in which Na⁺ binding is the potential-dependent step (Na⁺ well concept) also provides an appropriate kinetic fit to the experimental data, and must be considered as a possible mechanistic basis for function of the system.     

Ecological aspects of a silicified bivalve fauna from the Silurian of Gotland

The silicified Wenlockian (Silurian) bivalve fauna from MÖllbos, Gotland, is part of a life assemblage. The vast number of shells show unusual phenomena, e.g. shell repair, pearl and tumour formation, etc. A number of shells contain epibionts and bored, round holes. Presumptive predators of the bivalve community are discussed. Size-frequency distribution of the two most abundant species possibly reflects age classes. The fauna, comprising eleven species, is dominated by deposit-feeders (90 %). They exhibit niche diversification, including at least three different feeding levels within the sediment.     

Lipids of Pinus halepensis pollen

The total lipids of Pinus halepensis pollen were separated into individual classes of neutral and polar lipids and the components of each class were identified and determined quantitatively. Free fatty acids, waxes and triacylglycerols were found as the main constituents of neutral lipids and phosphatidylcholine and phosphatidylethanolamine of polar lipids. Glycerylether derivatives were detected in neutral and polar lipid fractions. Free and esterified volatile fatty acids were also found in pollen and its neutral lipid fraction.     

Radioimmunoassay for determination of indole-3-acetic acid in fungi and plants

A radioimmunoassay technique for indole-3-acetic acid is described. The method has successfully been used to measure extractable indole-3-acetic acid in fungal and plant materials and is able to detect as little as 0.3 pmol. As non-radioactive antigen the methyl ester of indole-3-acetic acid is used and the radioactive antigen is tritiated. An acid-catalyzed esterification of indole-3-acetic acid is used for conversion into methyl ester. The measuring range of the assay is 0.3–10 pmol. In the assay, separation of free and bound fractions is achieved by dextran-coated charcoal, leaving the bound fraction in the supernatant.     

Characterisation of the magnesium status of soils by means of the EUF-Mg fractions

Summary On the basis of pot experiments carried out on soils with different Mg contents using ryegrass, it could be established that Mg uptake by ryegrass is closely related to Mg in the EUF extracts. The Mg contents in the EUF extracts are therefore suitable indices of actually and potentially available Mg in soils.The ratio between Mg in the EUF extracts and Mg deposited on the electrode + filter varies. The absolute amount of Mg in the EUF extracts increases with increasing Mg content of the soils. The higher, however, the total desorbable Mg the lower are the Mg contents in the EUF extracts in comparison with the Mg contents deposited on electrode + filter. Besides total desorbable Mg the EUF-Mg fractions are influenced as well by the organic and inorganic CEC and by soil pH. The amount of EUF filtrate flowing through filter and electrode also has an influence on the amount of Mg in the EUF filtrate.Consequently for a proper evaluation of available soil Mg total EUF-Mg (Mg in the EUF filtrate + Mg deposited on electrode + filter) should be used.     

Discrimination of alfalfa weevil strains by allozyme analysis

Allozyme profiles of eastern weevils (Beltsville, Maryland; Washington Co., Illinois), western weevils (Logan and St. George, Utah), and Egyptian weevils (Yuma, Arizona; Westmorland, California) were compiled by acrylamide gel electrophoresis. Twenty-two gene loci from 12 enzymes (ACPH, ADH, AMY, AO, EST, GOT, G-6PDH, MDH, ME, SOD, TYR, XDH) were analyzed. Mean heterozygosity of these populations was 0.231, with an average proportion of polymorphic loci of 0.536. The mean genetic distance of all weevil populations was 0.033 and the fixation index was 0.024. Diagnostic loci were found which could distinguish western weevils from eastern and Egyptian weevils. The small genetic distance between the eastern and Egyptian weevils suggests that they may be the same strain and are certainly different from the western weevil strain. Based on this and other evidence, we conclude that all weevil strains in the United States are Hypera postica (Gyllenhal), and that the use of H. brunneipennis (Boheman) for the Egyptian alfalfa weevil of North America should be discontinued.

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Résumé Les allozymes d'Hypera de l'est des USA (Beltsville, Maryland; Washington Co., Illinois), de l'ouest des USA (Logan et St Georges, Utah) et égyptiens (Yuma, Arizona; Westmorland, Californie) ont été analysés par électrophorèse sur gel d'acrylamide. L'étude a porté sur 22 loci de 12 enzymes (ACPH, ADH, AMY, AO, EST, GOT, G-6PDH, MDH, ME, SOD, TYR, XDH). L'hétérozygotie moyenne de la population était 0.231, avec une moyenne de loci polymorphes de 0.536. La distance génétique moyenne de l'ensemble des populations était de 0.033 et l'indice de fixation de 0.024. Des loci caractéristiques ont été trouvés qui pourraient permettre de distinguer les Hypera occidentaux des orientaux et des égyptiens. La faible distance génétique entre les Hypera orientaux et égyptiens suggère qu'ils appartiennent à la même souche et sont certainement différents des occidentaux. A partir de cela et d'autres éléments, nous concluons que tous les Hypera des USA sont H. postica Gyllenhal et que l'utilisation d'H. brunneipennis Boheman pour désigner les Hypera égyptiens d'Amérique du Nord doit être abandonnée.

     

The cellular parameters of leaf development in tobacco: a clonal analysis

The cellular parameters of leaf development in tobacco (Nicotiana tabacum L.) have been characterized using clonal analysis, an approach that provides unequivocal evidence of cell lineage. Our results indicate that the tobacco leaf arises from a group of around 100 cells in the shoot apical meristem. Each of these cells contributes to a unique longitudinal section of the axis and transverse section of the lamina. This pattern of cell lincage indicates that primordial cells contribute more or less equally to the growth of the axis, in contrast to the more traditional view of leaf development in which the leaf is pictured as arising from a group of apical initials. Clones induced prior to the initiation of the lamina demonstrate that the subepidermal layer of the lamina arises from at least six files of cells. Submarginal cells usually divide with their spindles parallel to the margin, and therefore contribute relatively little to the transverse expansion of the lamina. During the expansion of the lamina the orientation and frequency of cell division are highly regulated, as is the duration of meristematic growth. Initially, cell division is polarized so as to produce lineages that are at an oblique angle to the midrib; later cell division is in alternating perpendicular planes. The distribution of clones generated by irradiation at various stages of development indicates that cell division ceases at the tip of the leaf when the leaf is about one tenth its final size, and then ceases in progressively more basal regions of the lamina. Variation in the mutation frequency within the lamina reflects variation in the frequency of mitosis. Prior to the mergence of the leaf the frequency of mutation is maximal near the tip of the leaf and extremely low at its base; after emergence, the frequency of mutation increases at the base of the leaf. In any given region of the lamina the frequency of mutation is highest in interveinal regions, and is relatively low near the margin. Thus, both the orientation and frequency of cell division at the leaf margin indicate that this region plays a minor role in the growth of the lamina.Abbreviation MF mutation frequency