Distinction between light-mediated and light-independent variations in phytoplankton production rates

An array of factors simultaneously controls phytoplankton photosynthesis and hence the primary production process. Because their relative importance shifts both with depth and with season, the significance of individual factors cannot be resolved by in situ incubations, even if all relevant environmental and biotic variables are measured.Here a procedure is described by which in addition to in situ measurements, photosynthesis is simultaneously assessed in identical subsamples under constant temperature (10 °C) and light (0.66 mol m^–2 h^–1 PAR conditions, in vitro). By calculating photosynthesis per unit of chlorophyll, effects of shifting biomass on photosynthesis can be eliminated but seasonal variations of light-saturated photosynthesis generated by temperature, and vertical changes of light-requirements (e.g. by light-shade adaptation) remain obscure. Quotients of in situ photosynthetic rates divided by in vitro rates allow the quantification of light-mediated changes. Provided that photosynthesis measured in vitro is light-saturated, quotients in situ: in vitro rates should never exceed unity. They are a measure for the degree of light-limitation. In vitro rates normalized to chlorophyll give information on temporal changes caused by variations in photosynthetic capacity. In Lake Constance, mean cell size appears to control light-saturated assimilation numbers.     

Effect of Moniliformis moniliformis density on distribution within the definitive host population (Rattus norvegicus)

The population dynamics of Moniliformis moniliformis was studied in ‘free-ranging’ laboratory rats, Rattus norvegicus, presented with different relative density levels of M. moniliformis in cockroaches, Periplaneta americana. Changes in selected population parameters of the negative binomial distribution were evaluated as indicators of changes in aggregation. A significant increase in the degree of aggregation of parasites occurred as a result of the increase in relative density of infective stages available to the rats. This increase in aggregation was due to the increase in over-dispersion that occurred in female rats only. The degree of aggregation in females was found to be significantly higher than that in males at both treatment levels. The best indicators of the degree of aggregation were found to be the ratio of the variance to the relative density and the ratio of the log-variance to log-relative density. Changes in k were not correlated with changes in over-dispersion or the relative density.     

The epithelium overlying rabbit bronchus-associated lymphoid tissue does not express the secretory component of immunoglobulin A

Summary The epithelium associated with lymphoid aggregates in the bronchial tract (BALT) was studied in rabbits by immunohistochemistry using monoclonal antibodies against the secretory component (SC) of IgA. The normal bronchus epithelium was intensely labelled. In contrast, epithelium overlying the central parts of the follicles was negative. This specialized epithelium cannot participate in the SC-mediated transport of IgA, which might be a basis for the adherence and transport of microorganisms into the lymphoid tissue, thus initiating immune responses of the BALT.     

Pulsed-field gel electrophoresis analysis of the genome of Streptomyces ambofaciens strains

The genome of four Streptomyces ambofaciens strains from different geographical origins (ATCC15154, DSM40697, ETH9247 and ETH 11317) was analysed by pulsed-field gel electrophoresis (PFGE). The PFGE technique has allowed the study of the extrachromosomal content of these strains and the characterization of their genomic DNA by restriction analyses. Electrophoretic migration of undigested DNA allowed us to detect a 80 kb-length linear molecule with concatemeric forms in S. ambofaciens ATCC15154. These extrachromosomal molecules were shown to be homologous to the circular plasmid pSAM1 (80 kb) suggesting that pSAM1 could exist not only in circular form but also in linear form. In the same way a 45 kb-length linear molecule was detected in S. ambofaciens ETH9427 and ETH11317. In contrast, no extrachromosomal DNA could be detected in S. ambofaciens DSM40697. The analysis of the macrorestriction patterns using the rate-cutting enzymes AseI and DraI indicated a close relationship between the DSM- and ETH- strains. Indeed, three types of restriction patterns were distinguished: while S. ambofaciens ETH9427 and ETH11317 were characterized by the same pattern and share more than 75% of comigrating fragments with the strain DSM40697, S. ambofaciens ATCC15154 exhibited a restriction pattern different from the other three. The total genome sizes of S. ambofaciens ATCC15154, DSM40697, ETH9427 and ETH11317 were estimated to be about 6500, 8000, 8200 and 8200 kb, respectively.     

65Zinc uptake from blood into brain and other tissues in the rat

Zinc is essential for normal growth, development and brain function although little is known about brain zinc homeostasis. Therefore, in this investigation we have studied⁶⁵Zn uptake from blood into brain and other tissues and have measured the blood-brain barrier permeability to⁶⁵Zn in the anaesthetized rat in vivo. Adult male Wistar within the weight range 500–600 g were used.⁶⁵ZnCl₂ and [¹²⁵I]albumin, the latter serving as a vascular marker, were injected in a bolus of normal saline I.V. Sequential arterial blood samples were taken during experiments that lasted between 5 min and 5 hr. At termination, samples from the liver, spleen, pancreas, lung, heart, muscle, kidney, bone, testis, ileum, blood cells, csf, and whole brain were taken and analysed for radio-isotope activity. Data have been analysed by Graphical Analysis which suggests⁶⁵Zn uptake from blood by all tissues sampled was unidirectional during this experimental period except brain, where at circulation times<30 min,⁶⁵Zn fluxes were bidirectional. In addition to the blood space, the brain appears to contain a rapidly exchanging compartment(s) for⁶⁵Zn of about 4 ml/100g which is not csf.     

Patterns of intraspecific variation inAntennaria alborosea,A. corymbosa,A. marginata,A. microphylla,A. parvifolia,andA. umbrinella (Asteraceae:Inuleae)

Patterns of intraspecific variation were examined inAntennaria alborosea A. E. Porsild,A. corymbosa E. Nels,A. marginata Greene,A. microphylla Rydb.,A. parvifolia Nutt., andA. umbrinella Rydb. AlthoughA. alborosea was initially considered arctic in distribution, it became apparent that a southern montane element also exists. Our results suggest that morphological differences between arctic and southern montane specimens represent clinal variation. The additional morphological data for specimens that occur more than 1,500 km south of the species' range as it was initially described result in a better understanding of this once presumed arctic taxon. Morphological variation in the dioecious speciesA. corymbosa, A. marginata, A. microphylla, A. parvifolia, andA. umbrinella was greater between the genders than was geographic variation within each gender. These results demonstrate that both pistillate and staminate specimens must be examined in dioecious species ofAntennaria if morphological variation in the respective species is to be fully understood. Character size or number of broadly distributed species (A. microphylla andA. parvifolia) generally decreased with increasing longitude, whereas characters of species with more restricted distributions (A. alborosea, A. corymbosa, andA. marginata) generally increased in size or number with increasing latitude or longitude.Antennaria umbrinella was an exception in this respect.     

Studies on theStellaria longipes complex (Caryophyllaceae): Isozyme variability and the relationship betweenStellaria longipes andS. longifolia

Genetic variation within and the relationship betweenStellaria longipes Goldie andS. longifolia Muhl. were studied. Ten enzyme systems were assessed in eight natural populations ofS. longipes (25 loci) and three ofS. longifolia (20 loci) using starch and polyacrylamide gel electrophoresis. Patterns of population differentiation corresponded to geographic distance. There was no evidence that polyploidS. longipes had greater electrophoretic variability than diploidS. longipes. The isozyme data confirmed extensive population differentiation in these species and, within that context, a relatively close relationship betweenS. longipes andS. longifolia. It was postulated that diploids of these two species might be the progenitors of tetraploidS. longipes.     

Analysis of rice (Oryza sativa L.) genome using pulsed-field gel electrophoresis and rare-cutting restriction endonucleases

TheOryza sativa (rice) genome is small (600 to 900 megabase pairs) when compared to that of other monocotyledonous plants. Rice was the first of the major cereals to be successfully transformed and regenerated. An RFLP map with approximately 300 markers is readily available, and the DNA content per map unit is only two to three times that ofArabidopsis thaliana. Rice is also the main staple food for the majority of peoples in the world. We developed techniques for the preparation of intact genomic DNA from Indica and Japonica subspecies of rice, used statistical methods to determine which restriction endonucleases are rare-cutting, and used pulsed-field gel electrophoresis (PFE) to separate large fragments of rice DNA. Southern hybridization to blotted rice PFE gels was used to show that the digests were complete. The long-term goal of our work is to generate an integrated genetic/physical map for the rice genome, as well as helping to establish rice as a model for map-based gene cloning and genome analysis.     

Information transmission during intra- and interspecific courtship inEphestia elutella andCadra figulilella

Using information theory, courtship posturing in the moths Ephestia elutella(Hübner) and Cadra figulilella(Gregson) was analyzed for information transmission, which was partitioned into autocovariability (intraindividual transmission) and cross-covariability (interindividual transmission). This two-factor analysis was sufficient to account for more than 60% of the behavioral variance in males of E. elutellaand in both sexes of C. figulilelladuring intraspecific courtships; however, there were large residual variances in the behavior of male and female C. figulilelladuring interspecific courtships and in E. elutellafemales during both inter- and intraspecific courtships. In E. elutella,significant levels of transmission were attributable to both inter- and intraindividual effects, whereas in C. figulilella,only autocovariability was high and no interindividual communication could be assigned to courtship postures. Although courtship in these two species was qualitatively very similar and males readily courted nonconspecific females, high levels of reproductive isolation resulted from courtship. Male C. figulilellahad 94% fewer copulations with E. elutellafemales than with conspecific females and E. elutellamales had 78% fewer copulations with C. figulilellafemales than with conspecifics. These reductions were due to a differential response in both females and males, causing inter-specific courtships to be terminated much earlier than intraspecific courtships. This discrimination indicates that interindividual communication was indeed occurring during courtship and was only partially measured by analysis of postures. Thus, communication took place largely in some other modality, most likely the chemical modality, where species specificity is suggested for both male and female pheromones.