Predation at a snail's pace: what's time to a gastropod?

Summary Predation by naticid gastropods shows evidence of adaptation to maximize the rate of energy intake. The predation rate of Polinices duplicatus feeding on artificially altered, thin-shelled Mercenaria mercenaria was faster than the predation rate on normal Mercenaria. The rate of energy intake was limited by handling time. The time saved by predation on thin-shelled prey was used to forage. Thus time was shown to be valuable to P. duplicatus, and cost-benefit functions using time and energy as currencies are appropriate for estimating dietary efficiency and predicting prey choice.Despite the clear superiority of thin-shelled prey, P. duplicatus did not learn to prefer this novel prey type, suggesting that predator choices are sterotyped, reflecting optima selected over evolutionary time.     

Plasma levels of arginine vasotocin,prolactin, aldosterone and corticosterone during prolonged dehydration in the domestic flowl: effect of dietary NaCl

Three groups of White Plymouth Rock laying hens were adapted to three levels of dietary NaCl: low-NaCl food with tap water (LOW), high-NaCl food (1% NaCl w/w added) with tap water (HT), and high-NaCl food with 0.5% NaCl for drinking (HS). The birds were subjected to water deprivation (dehydration) for 18 days. Blood sampling was done at 2-4 day intervals. Plasma concentrations of arginine vasotocin (AVT), prolactin (PRL), aldosterone (ALDO) and corticosterone (CS) were determined by radioimmunoassay. Plasma osmolality, sodium, chloride, and potassium were also determined. In the normally hydrated hens fully adapted to the diets, there was a stepwise increase from LOW to HS in plasma osmolality (305, 315, 332 mOsm, for LOW, HT and HS, respectively), [Na+] (144, 153, 161 mM) and [Cl-] (109, 119, 127 mM) as well as in [AVT] (6, 14, 18 pg/ml) and [PRL] (16, 24, 34 ng/ml). Regressing [AVT] on osmolality gave a slope of 0.30 pg . ml-1/mOsm and a threshold of 273 mOsm. The slope of [PRL] on osmolality was 0.73 ng . ml-1/mOsm. The correlation coefficient of [AVT] and [PRL] was 0.67. LOW had high [ALDO] (165 pg/ml) which was suppressed to low levels in HT and HS (5-8 pg/ml), while [CS] was the same in all groups (0.9-1.1 ng/ml). Plasma [K+] was decreased in the high-NaCl groups (5.8 mM in LOW, 4.4 and 4.7 mM in HT and HS). Dehydration resulted within 2 days generally in a sharp (5-15%) increase in osmolality, [Na+] and [Cl-], which thereafter increased more slowly during the remaining 16 days in all groups, with the slowest increase in LOW. The levels of osmolality [Na+] and [Cl-] were 5% lower in LOW than in HT and HS, which showed the same levels during the dehydration period. Plasma [AVT] and [PRL] increased 2-4 fold within 2 days of dehydration; [AVT] reached a plateau at 29 pg/ml in all groups, but [PRL] continued to rise in all groups, fastest in LOW, reaching similar levels in all groups after 14-18 days of dehydration, about 85 ng/ml. The correlation coefficient of [AVT] and [PRL] was decreased by half (to 0.32) during dehydration. Plasma [ALDO] increased in all groups with dehydration, 1.7 fold in LOW and 3-6 fold in HT and HS, but the levels reached in HT and HS were only 15-30% of that seen in LOW.(ABSTRACT TRUNCATED AT 400 WORDS)     

Conductimetric assessment of the biomass content in suspensions of immobilised (gel-entrapped) microorganisms

Summary The problem of obtaining a rapid estimate of the microbial content of an immobilised cell suspension is addressed. The low-frequency conductivity of free-living cell suspensions of Clostridium pasteurianum is lower than that of the medium in which they are suspended, by an amount conforming to the Bruggeman relation. The conductivity of the cell wall makes a negligible contribution to the measured conductivity under the conditions used. Calcium alginate beads (lacking microbial cells) lower the conductivity of a solution with which they have been equilibrated by an extent which is a function of the concentration of alginate gel used in forming the beads. When this is taken into account, the ratio of the conductivity of a suspension of gel-immobilised cells to that of the suspending medium can be used to give a rapid and convenient assessment of the amount of microbial biomass present.     

Rat esophageal and epidermal keratinocytes: intrinsic differences in culture and derivation of continuous lines

Serially cultivated with 3T3 feeder layer support as colonies of stratified squamous epithelium, rat epidermal and esophageal epithelial cells were readily distinguishable by three criteria. First, the epidermal colonies, exhibiting extensive piling up of squames in the centers, were more stratified than esophageal colonies. Second, in sparse culture 70 to 90% of the esophageal cells but as few as 1 to 5% of the epidermal cells were competent in cross-linked envelope formation upon treatment with the ionophore X537A. After reaching confluence, up to 90% of the cells of both types formed envelopes upon ionophore treatment. Third, epidermal cells in suspension culture reached maximal levels of spontaneously cross-linked envelopes in 1 day or less, while esophageal cells required about 4 days in suspension to reach maximal levels. A reproducible finding with both cell types was that initial colony-forming efficiencies of less than 1% increased to about 40% upon serial passage with consequent derivation of continuous lines. Sparse cultures of esophageal cells with high colony-forming ability retained a high degree of envelope competence (70 to 90%), indicating these two properties are not mutually exclusive. The derived lines exhibited reduced dependence upon feeder layer support at clonal density, but in suspension culture the cells did not grow and lost colony-forming ability with a half-time of several hours. We conclude that cells from these keratinized rat epithelia exhibit intrinsic differences in culture and become continuous lines expressing characteristic regulation of envelope competence and loss of germinative capability in suspension.     

Exceptional characteristics of amino proton exchange in guanosine compounds

Amino 1H NMR line width as a measure of amino proton exchange in guanosine compounds is completely unaffected by the addition of ca. 1 M tris(hydroxymethyl)-aminomethane, imidazole, 2-(N-morpholino)ethanesulfonic acid, glycine, or cacodylate, all shown to be effective buffer catalysts in adenosine and cytidine proton exchange. Line broadening, seen only with phosphate and acetate, is established by intermolecular interactions, as well as by amino to water proton exchange. This absence of buffer catalysis of exchange is accounted for by the relatively small implied effect of G(N-7) protonation on amino acidity, based on similar observations with 7-methylguanosine as a model for endocyclic protonation. The requirement for diffusion-controlled proton transfer in buffer catalysis is achieved by nucleobase protonation in adenine and cytosine, but not in guanine.     

Nitrogen fixation in grassland and associated cultivated ecosystems

Summary Nitrogen fixation in the natural, Agropyron-Koeleria grassland ecosystem was studied using the C₂H₂-C₂H₄ and N¹⁵ assays. Small soil samples and also undisturbed soil cores were used for analyses. Both techniques indicated that grassland and associated cultivated soils had low fixation rates (0.6–1.8 kg/ha per 28 days in the laboratory and, 1 kg/ha per season under actual field conditions). Algal colonies (Nostoc spp.) on the soil surface were active fixers when the surface of the grassland was moist. However, their small biomass limits the extent of fixation in most areas. In native grassland, 16 legumes bore nodules. The three most common speciesVicia americana, Thermopsis rhombifolia andOxytropis sericea, all of which had active nodules, contributed 10 per cent of the total nitrogenase activity. The non-legumesElaeagnus commutata andShepherdia argentea were profusely nodulated with active nodules, but were confined to specific habitats. No nodules were found onArtemisia orOpuntia spp. The major, heterotrophic, asymbiotic bacteria in the soil were clostridia. These utilize substrates produced by aerobic cellulose and hemicellulose degrading organisms to fix N in anaerobic microsites. The C₂H₂:N₂ reduction ratio was 3 to 1 in large, aerobic core samples, but was greater under water-logged conditions where high fixation rates occurred.     

Induction of alveolar epithelial injury by phospholipase A2

Severe damage to the alveolar type I epithelial cell is a characteristic morphological feature of lung injury due to numerous cases. It is postulated that excess phospholipase A2 (PLA2) activity might be responsible for these changes, as one of the naturally occurring products of this enzyme, lysophosphatidylcholine (lysoPC) has been shown to cause selective injury to the type I pneumonocyte when it is instilled into the lower air spaces of the lung. To further investigate this potential mechanism of type I epithelial cell toxicity, we have measured the epithelial permeability-surface area product (PS) for [14C]sucrose as well as whole-lung lysoPC content at several times after instilling PLA2 (Naja naja venom) into either the air spaces or the perfusate of an isolated hamster lung preparation. As a molar percentage of total phospholipids, the normal hamster lung contains approximately 1.5% lysoPC, and this value is not affected by fluid filling of the air spaces or perfusion of the excised lung for periods up to 90 min. When 0.15 U/ml PLA2 is instilled into the air spaces, lung lysoPC content increases to approximately 2.5% and there are barely detectable increases in [14C]sucrose PS. With air space PLA2 concentrations of 0.30 U/ml, lysoPC content increases to between 4 and 5%, [14C]sucrose PS increases by greater than a factor of 10, and flooding of the alveolar spaces occur. Ultrastructural studies of similarly treated lungs show widespread but selective damage to the type I epithelial cells. These same biochemical and functional changes are not seen when the same concentrations of PLA2 are added to the lung perfusate.(ABSTRACT TRUNCATED AT 250 WORDS)