Interaction between the Effects of Inside and Outside Na and K on Bullfrog Skin Potential

The composition of the solution bathing one border of the isolated frog skin affects the response of the potential across the skin to changes in the composition of the solution bathing the opposite border. Increasing the K concentration of the inside (corium) bathing solution decreased the sensitivity of the potential to a change in outside Na concentration. Decreasing the outside Na concentration decreased the sensitivity of the potential to a change in inside K concentration. Increasing the total ionic strength of the outside bathing solution or of both bathing solutions decreased the sensitivity of the potential to a change in outside Na concentration.     

EVOLUTIONARY AND GEOGRAPHIC TRENDS IN ADAPTIVE WOOD ANATOMY IN ERIASTRUM DENSIFOLIUM (POLEMONIACEAE)

Anatomical features of Eriastrum densifolium populations in southern California show variation that correlates well with ecological setting and geographical distribution. Vessel element size and density in shoots suggest strong adaptation among different subspecies to efficient water movement in different habitats. Indices of mesomorphy, devised by Carlquist to indicate relative adaptivity of wood, likewise show considerable variation among populations, suggesting that different subspecies have anatomical components that can define them. Relationships among the five subspecies of E. densifolium may be explored through MI value relationships.     

Ciliate communities in shallow groundwater: seasonal and spatial characteristics

1. Ciliated protozoans (Phylum Ciliophora) were collected from five sites in a shallow groundwater system in southern Ontario, Canada over a 13‐month period: one at the spring source, two along the channel banks, and two in the stream channel. Ciliates and environmental data were collected from surface water and at five depths into the sediment, located at 20, 40, 60, 80 and 100 cm. 2. Species richness was high (170 ciliate species belonging to 89 genera were identified) and variable, both spatially and temporally. Highest species richness (86) occurred between 20 and 60 cm, and typically decreased below 60 cm. 3. Ciliate densities were also seasonally and spatially variable. Densities peaked in March between 40 cm (as high as 69 900 cells L⁻¹) and 60 cm, and again in May and June at 80 and 100 cm. Densities were lowest in winter. The surface‐water ciliate community had a different species composition and lower population densities. 4. At all depths, small (<50 μm) bacterivorous ciliates typically dominated, but omnivorous and predatory species were also present (combined, up to 30% of the average density). 5. Several ciliate genera, traditionally considered planktonic, occurred at low densities from 40 cm down to 100 cm. 6. Ordination analysis indicated that the main factors influencing the shallow groundwater ciliate communities were depth and temperature. 7. Dissolved oxygen also appeared to influence these communities in that they typically comprised genera that preferred either low‐oxygen or anaerobic conditions.     

Estimation of Tissue Construction Cost from Heat of Combustion and Organic Nitrogen Content

Abstract. We present a method for estimating the construction costs of plant tissues from measurements of heat of combustion, ash content, and organic nitrogen content. The method predicts glucose equivalents, the amount of glucose required to provide carbon skeletons and reductant to synthesize a quantity of organic product. Glucose equivalents have previously been calculated from the elemental composition of tissue. We define construction cost as the amount of glucose required to provide carbon skeletons, reductant and ATP for synthesizing the organic compounds in a tissue via standard biochemical pathways. The fraction of the total construction cost of a compound or tissue (excluding costs of transporting compounds) that is reflected in its glucose equivalents is the biosynthetic efficiency ( E _B). This quantity varies between 0.84 and 0.95 for tissues with a wide range of compositions. Using the new method, total construction cost can be estimated to ± 6% of the value obtained from biochemical pathway analysis.
Construction costs of leaves of three chaparral species were estimated using the proposed method and compared to previously published values, derived using different methods. Agreement among methods was generally good. Differences were probably due to a combination of inaccuracy in the estimated biosynthetic efficiency and technical difficulties with biochemical analysis, one of the older methods of determining construction cost.     

Survey of chemical speciation of trace elements using synchrotron radiation

Information concerning the chemical state of trace elements in biological systems generally has not been available. Such information for toxic elements and metals in metalloproteins could prove extremely valuable in the elucidation of their metabolism and other biological processes. The shielding of core electrons by binding electrons affect the energy required for creating inner-shell holes. Furthermore, the molecular binding and symmetry of the local environment of an atom affect the absorption spectrum in the neighborhood of the absorption edge. X-ray absorption near-edge structure (XANES) using synchrotron radiation excitation can be used to provide chemical speciation information for trace elements at concentrations as low as 10 ppm. The structure and position of the absorption curve in the region of an edge can yield vital data about the local structure and oxidation state of the trace element in question. Data are most easily interpreted by comparing the observed edge structure and position with those of model compounds of the element covering the entire range of possible oxidation states. Examples of such analyses will be reviewed.     

Influence of various soil factors on the effects of ferulic acid on leaf expansion of cucumber seedlings

Summary Cucumber seedlings were grown in a Portsmouth soil-sand system to study how varying soil clay and organic matter content might modify cucumber seedling response to ferulic acid, a reported allelopathic agent. Leaf area expansion of cucumber seedlings, soil respiration, and soil solution concentrations of ferulic acid were monitored. Leaf area, mean absolute rates of leaf expansion, and shoot dry weight of cucumber seedlings were significantly reduced by ferulic acid concentrations ranging from 10 to 70 μg/g dry soil. Ferulic acid was applied every other day, since it rapidly disappeared from soil solution as a result of retention by soil particles, utilization by microbes and/or uptake by roots. The amount of ferulic acid retained (i.e., adsorbed, polymerized,etc.) by soil particles appeared to be secondary to microbial utilization and/or uptake by roots. Varying clay (5.3 to 9.8 g/cup) and organic matter (2.0 to 0.04g/cup) contents of the soil appeared to have little impact on the disappearance of ferulic acid from soil solution under “ideal” growth conditions for cucumber seedlings unless larger amounts of ferulic acid were added to the soil; in this case 200 μg/g. The addition of ferulic acid to the soil materials substantially increased the activity of the soil microbes. This latter conclusion is based on recovery of ferulic acid from soil solution and soil respiration measurements. Paper No. 10347 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh, N C 27695-7601. The use of trade names in this publication does not imply endorsement by the North Carolina Agricultural Research Service of the product named, nor criticism of similar ones not mentioned.     

The history and chronology of siwalik cercopithecids

Cercopithecid monkeys make a comparatively late appearance in the Miocene Siwalik formations of the Indian Subcontinent. The oldest well-dated specimen is a 6.3 MY old colobine, ?Presbytis sivalensis, and it is doubtful that any cercopithecids were present in the Siwalik faunas prior to 7.0 MY, a date that is considerably later than estimates for their appearance elsewhere in Eurasia. Cercopithecines appear later than colobines. Although their temporal ranges are uncertain, cercopithecines evidently were not present before 3.2 MY and possibly not until 2.5 MY. They are represented by three species,?Macaca palaeindica, Procynocephalus subhimalayanus, andTheropithecus delsoni. In the Siwaliks the appearances of colobines and cercopithecines coincide with or follow shortly after major faunal changes that also bring other northern Eurasian and African taxa into the region.     

High-dose,unlabeled, nonspecific antibody pretreatment: influence on specific antibody localization to human melanoma xenografts

Summary Nonspecific uptake of radiolabeled monoclonal antibodies in normal tissues is a significant problem for tumor imaging. A potential means of decreasing nonspecific antibody binding is to blockade nonspecific antibody binding sites by predosing with cold, nonspecific isotypematched antibody, before injecting specific antibody. Nontumor-specific murine monoclonal antibody LK2H10 (IgG1) or Ab-1 (IgG2a) was given i.v. at doses of 0 to 3.5 mg to nude mice with xenografts of human melanoma. These mice were then given i.v. 4 g of ¹³¹I anti-high molecular weight antigen of melanoma (HMWMAA) monoclonal antibody 763.24T (IgG1) or 225.28S (IgG2a), respectively. These mice were also given a tracer dose of ¹²⁵I LK2H10 or Ab-1, respectively. Specific tumor uptake of anti-HMWMAA antibodies was see in all cases. No drop in tumor or nontumor uptake was demonstrated for either of the tumor-specific or nonspecific monoclonal antibodies due to nonspecific monoclonal antibody pretreatment. These data suggest that high doses of isotype-matched unlabeled nonspecific monoclonal antibody given before ¹³¹I tumor-specific monoclonal antibody, will not enhance tumor imaging. Present address: Hybritech, San Diego, CA, USA     

Why are there so many species of bumble bees at Dungeness?

WILLIAMS, P. H., 1989. Why are there so many species of bumble bees at Dungeness? Dungeness is unique in the British Isles in that it has more species of bumble bees than any other locality. Three ideas about what governs the number of species at a locality are examined by locking at patterns of flower visits at Dungeness in comparison with those at Shoreham, a species-poor locality also in Kent. The species of bumble bees that are present at Dungeness but absent from Shoreham show no association in their distributions among 2 km grid-squares in Kent with the species of food-plants that they prefer at Dungeness, nor is there any correlation between the diversity of bees and diversity of food-plants at Dungeness and Shoreham. From the information available, Dungeness is most likely to have more species of bumble bees because it has a particularly high density of the more nectar-rich flowers that bumble bees can use. Bumble bees feed most profitably from deep flowers because these contain more nectar than shallow flowers, although direct access to deeper flowers is ultimately limited by the length of each bee's proboscis. The distribution of worker proboscis lengths among species in the species-pool in Kent is clumped about a median of 7.9 mm. The best foraging conditions for the maximum number of species should be provided when flowers of similar depths are present in sufficiently large numbers for all foragers to make near-optimal flower choices. Although there is no difference in median between the distributions of the bees' proboscis lengths and the depths of the flowers they use at Dungeness, at Shoreham the flower depths used are shorter than the proboscis lengths. Among the food-plants at Dungeness, high densities of Teucrium scorodonia and Echium vulgare are likely to be especially important.     

UV irradiation inhibits initiation of DNA replication from oriC in Escherichia coli

Summary Irradiation of Escherichia coli with UV light causes a transient inhibition of DNA replication. This effect is generally thought to be accounted for by blockage of the elongation of DNA replication by UV-induced lesions in the DNA (a cis effect). However, by introducing an unirradiated E. coli origin (oriC)-dependent replicon into UV-irradiated cells, we have been able to show that the environment of a UV-irradiated cell inhibits initiation of replication from oriC on a dimer-free replicon. We therefore conclude that UV-irradiation of E. coli leads to a trans-acting inhibition of initiation of replication. The inhibition is transient and does not appear to be an SOS function.