Suspended bacteria in calcareous and acid headstreams: abundance, heterotrophic activity and downstream change

SUMMARY. 1. Concentration of total suspended bacteria and heterotrophic activity (as turnover rate and turnover rate per bacterium for glucose assimilation by a trace-addition approach) were determined at distance intervals along four high-trophic-status calcareous headstreams in the Yorkshire Worlds and along four low-tropic-status acid headstreams in the Galloway Hills.
2. Mean concentration of suspended bacteria was marginally greater in the calcareous streams while turnover rate and turnover rate per bacterium were substantially greater.
3. Further determinations of heterotrophic activity (as turnover rate, turnover rate per bacterium, V_max and V_max per bacterium for glucose mineralization by a kinetic approach) supported the conclusion that heterotrophic activity was greater in the calcareous streams.
4. Mean cell volume of suspended bacteria, measured by electron microscopy, was found to be greater in the calcareous streams.
5. In the calcareous streams the concentration of total bacteria and turnover rate usually increased substantially, in a straight-line relationship, with distance downstream from the source. In the acid streams such downstream increase was less usual, the rate of increase per unit length of stream was less, curvilinear relationships were more frequent and on some occasions downstream decrease was observed.
6. The calcareous and acid streams thus formed two distinct groups on the basis of heterotrophic activity, cell volume and rate of downstream increase of suspended bacteria. This division was not necessarily caused solely by difference in pH but might be due to the combined effects of the many environmental variables which change in parallel with pH.     

Reproductive biology of Cyrtopodium punctatum in situ: implications for conservation of an endangered Florida orchid

Cyrtopodium punctatum (Linnaeus) Lindley is an endangered epiphytic orchid restricted in the USA to southern Florida. This species has been extensively collected from the wild since the early 1900s, and today only a few plants remain in protected areas. As part of a conservation plan, a reproductive biology study was conducted to better understand the ecology of this species in Florida. Cyrtopodium punctatum relies on a deceit pollination system using aromatic compounds to attract pollinators. Nine aromatic compounds were identified as components of the fragrance of C. punctatum inflorescences, including two compounds that are known to be Euglossine bee attractants. However, this group of bees is not native to Florida. Of the four bee species observed to visit C. punctatum flowers in the present study, carpenter bees ( Xylocopa spp.) are likely to be the main pollinators. Pollination experiments demonstrated that C. puntatum is self-compatible, but requires a pollinator and thus does not exhibit spontaneous autogamy. In addition, the rates of fruit set were significantly higher for flowers that were outcrossed (xenogamy) than for those that were self-crossed. Thus, the species has evolved a degree of incompatibility. Examples of natural pollination and fruit set were observed during the present study (2007–2008), but the rates of reproduction were modest as a consequence of the low plant numbers and possible changes in insect densities as a result of anthropogenic influences.     

Melanocortin Receptors: Identification and Characterization by Melanotropic Peptide Agonists and Antagonists

Hormones are chemical messengers released from cells to act on and control the activity of other cells. Hormonal ligands initiate their actions by interacting with receptive substances (Langley, 1906) of the target cells. These receptors are proteins that are either integral components of the cell membrane or are localized cytoplasmically within cells. Ligand-receptor interaction results in either the stimulation or inhibition of cellular activity. Since most hormones bind rather specifically to receptors possessed by their target cells, labeling of hormonal ligands can be utilized to identify and localize cells within an animal. In this report we discuss what is presently known about melanocortin receptors (MCRs) as studied by the use of labeled melanotropic peptide ligands.     

Characterization of microsatellite loci in Ipomopsis (Polemoniaceae) wildflowers

Members of the Ipomopsis aggregata species complex in the phlox family (Polemoniaceae) often hybridize when they occur in sympatry, and thus have been extensively studied to examine processes involved in plant speciation. I developed 12 microsatellite loci in I. aggregata that are also polymorphic in closely related Ipomopsis tenuituba, producing an average of eight alleles per locus in test populations of 12 individuals per species. Several of these markers also successfully amplified in other Ipomopsis species and more distant members of the Polemoniaceae, suggesting they should prove useful for a broad range of evolutionary studies in this widely distributed system.     

A note on the efficiency of stomaching for the quantitative removal of epiphytic bacteria from submerged aquatic plants

The effect of stomaching time on release of epiphytic bacteria from two species of submerged macrophytes was investigated, and the proportion of total epiphytes released from three species by stomaching was determined. A duration of 5 min was found to be an adequate stomaching time; the proportion released (mean ca 0.4) varied considerably between sites and sampling occasions.     

Chemical Carcinogenesis in Mice inhibited by Interferon

SEVERAL experiments have demonstrated that the anti-viral substance, interferon, can inhibit the growth of spontaneous^1,2, transplanted³ and virus-induced neoplasms in mice^4–7. Lieberman et al.⁵ reported that interferon treatment partially suppressed X-radiation-induced leukaemia in C57B1/6 mice. As they pointed out, the inhibitory effect provided additional evidence for the theory that X-rays cause lymphoma through the activation of a leukaemogenic type C RNA viral intermediate. In this communication, we report studies with CF-1 mice (Carworth Farms, New York City) to determine the effects of interferon on SC tumour induction by 3-methylcholanthrene (3-MC). These mice were previously shown to harbour high levels of type C RNA gs antigen and.infectious virus in normal spleens and in induced tumours, while spontaneous tumours rarely develop until late in life^8–10.     

Temporal variation in density of epiphytic bacteria on submerged vegetation in a calcareous stream

The density of epiphytic bacteria on (1) leaves, (2) stems and petioles, and (3) whole shoots of submerged Nasturtium officinale, Apium nodiflorum and Glyceria fluitans was determined from January to June 1984 in a calcareous stream in North Humberside. The density on leaves was less than on stems and petioles; reasons for this are suggested. The density on all three species decreased from late January to February-March and then increased to June. This temporal change was related to environmental variables (e. g. negative correlation with discharge and positive correlation with temperature), a situation which contrasts with Baker & Orr (1986) who found no such relationships in a Southern England chalk stream.