The use of mean pool abundances to interpret 15N tracer experiments

Details are presented of a simple mathematical framework that allows ¹⁵N tracer experiments to be interpreted in terms of the main processes of the soil/plant nitrogen cycle. The calculations, all of which can be performed on a scientific calculator, yield the rates of gross mineralization and nitrification and the crop nitrogen uptake occurring as ammonium and nitrate. Two procedures are presented. One requires paired experiments with labelled ammonium and unlabelled nitrate as one treatment, and unlabelled ammonium and labelled nitrate as the other. The second procedure requires only the labelled ammonium, unlabelled nitrate treatment. Example calculations are presented using actual experimental data. The interpretative procedure uses the fact that the rate of isotopic dilution in an ammonium pool labelled with ¹⁵N is a function of the rate at which unlabelled ammonium is introduced into the pool via mineralization. Similarly, the rate of isotope dilution in an ¹⁵N labelled nitrate pool is a function of the rate at which unlabelled nitrate is introduced into the pool via nitrification.     

Testing whether ecological factors promote cladogenesis in a group of tiger beetles (Coleoptera: Cicindelidae)

We investigate the role of ecological differentiation in cladogenesis of a monophyletic group of North American tiger beetles, the subgenus Ellipsoptera (genus: Cicindela), by reconstructing their species-level phylogeny from mitochondrial DNA sequences. Observed reconstructions of ecological characters on the phylogeny are compared to those expected under simple null models of no association with cladogenesis. We find no evidence that ecological disparity is associated with either species coexistence, speciation or long-term persistence and/or radiation of lineages. Ecomorphological traits have evolved in response to differences in habitat occupied by species, but without detectable relationship with cladogenesis.     

Inconsistent estimates of diversity between traditional and DNA taxonomy in bdelloid rotifers

Microscopic animals offer great potential in the analysis of spatial patterns of diversity, as they may provide different scenarios for biogeography and macroecology, but understanding diversity of microscopic animals is hampered by lack of comprehensive data on species distribution and by unreliable taxonomy. DNA taxonomy may prove useful in obtaining reliable data in the future, but we still do not know to what extent traditional and DNA taxonomy can be comparable for microscopic organisms. In this paper, we compare analyses and estimates of diversity at the level of species assemblage between traditional and DNA taxonomy for a group of moss-dwelling microscopic animals, bdelloid rotifers. The results are straightforward: Traditional species identification underestimates diversity by factors of 2 at the local and 2.5 at the regional scale. We discuss the results in the framework of current hypotheses on the distribution of microscopic animals.     

Screening the ability of rice roots to overcome the mechanical impedance of wax layers: importance of test conditions and measurement criteria

The development of a wax layer method for screening the ability of rice (Oryza sativa L.) roots to overcome mechanical impedance is described. Wax layers (3 mm thick) made of mixtures of white soft paraffin and paraffin wax were installed 50 mm deep in tubes of sand. The sand was watered with nutrient solution and planted with 3-d old rice seedlings. The numbers of root axes per plant that had penetrated the wax layers 24 d after planting were counted. The ratio of penetrated to total root axes per plant gave a misleading measure of root penetration ability, as rice varieties differed in the ratio of penetrated to total axes in a low impedance (3% wax) control. In non-flooded conditions, a 60% wax layer decreased root penetration (number of roots penetrating the wax layer per plant) to a mean of 74% of the low impedance control, whereas an 80% wax layer decreased mean root penetration to 31% of the control. The best measure of root penetration in non-flooded conditions was the number of axes penetrating an 80% wax layer. Flooding decreased root penetration of a 60% wax layer to a mean of 26% of the low impedance control. The best measure of root penetration in flooded conditions was the number of axes penetrating a 60% wax layer.     

Differentiation of simian virus 40 transformed human mammary epithelial stem cell lines to myoepithelial-like cells is associated with increased expression of viral large T antigen

Cloned simian virus 40 (SV40)-transformed human breast epithelial cell lines can differentiate to myoepithelial-like cells, and these can be isolated as clonal cell lines. Immunofluorescent and immunocytochemical analysis of such cell lines growing on plastic surfaces, collagen gels, and as tumor-nodules in nude mice indicate that all the cell lines produce SV40 large T antigen, but that the production of this antigen is qualitatively increased in the myoepithelial-like cells and cell lines. The myoepithelial-like cell lines produce 4-6 times more immunoprecipitable large T antigen than the parental epithelial cells. The amount of mRNA for large T antigen is also increased by 3.5-5-fold in the myoepithelial-like cell lines when analysed by dot-blot or by Northern hybridisations. Thus, differentiation along the myoepithelial-like cell pathway is associated in these SV40-transformed cells with increased expression of the viral large T antigen. It is suggested that immortalization of primary breast epithelial cell cultures may be, in part, due to the expression of large T antigen preventing processes of terminal keratinization.     

Elongated cells derived from rat mammary cuboidal epithelial cell lines resemble cultured mesenchymal cells in their pattern of protein synthesis

Two-dimensional gel electrophoresis has been used to identify polypeptide patterns characteristic of rat mammary cuboidal epithelial cells or mesenchyme-derived cells. Elongated cells and cell lines derived from cloned cuboidal epithelial cells in culture possess a polypeptide pattern which resembles that of the cultured mesenchymal cells rather than that of the cuboidal epithelial cells from which they were derived. These elongated converts also resemble cultured mesenchymal cells in possessing a Triton-insoluble matrix in which vimentin and not prekeratin predominates.