Isolation, fractionation and template activity of the continuously-condensed chromatin of Euglena gracilis

A technique for isolating whole chromatin from nuclei of the lower eukaryote Euglena gracilis is presented. This chromatin, which appears under the electron microscope as uniformly condensed fibers, can, nevertheless, be subfractionated into distinct heterochromatic and euchromatic fractions. The euchromatin, comprising about 14% of the total DNA of the nucleus, contains over 80 % of the total endogenous RNA polymerase activity measured. The K_m for this enzyme is higher than that found for prokaryotes, but falls in the range found for other eukaryotes. Stability constants, calculated from cation-chromatin binding data, suggest that internal carboxyl groups of chromosomal proteins, at least, are involved in the condensation of Euglena chromatin. The relationship between Euglena chromatin and that of higher eukaryotes is discussed.     

Daily temperature experience and selection by adfluvial bull trout (<Emphasis Type="Italic">Salvelinus confluentus</Emphasis>)

Bull trout (Salvelinus confluentus) are a thermally sensitive cold-water species with a threatened conservation status across much of North America. To improve our understanding of bull trout thermal ecology, we tagged more than 150 adults with temperature-sensing acoustic biotelemetry transmitters and monitored the animals in a British Columbia reservoir for two years. Thermal resource selection was estimated in open water from the summer to autumn as the system transitioned to isothermal conditions. On average, bull trout thermal history tracked seasonal changes and remained close to the optimum temperatures for growth and metabolism. As summer progressed, bull trout increasingly selected temperatures of 11–15 °C as they became less available within the water column. Selection indicated the movement to shallower waters where 11–15 °C temperatures existed. The results show that bull trout mainly occupy a narrow range of temperatures which suggests the importance of cold-water refuge for the species.     

Bryophyte physiological responses to, and recovery from, long-term nitrogen deposition and phosphorus fertilisation in acidic grassland

Atmospheric nitrogen deposition can cause major declines in bryophyte abundance yet the physiological basis for such declines is not fully understood. Bryophyte physiological responses may also be sensitive bioindicators of both the impacts of, and recovery from, N deposition. Here, responses of tissue nutrients (nitrogen (N), phosphorus (P) and potassium (K): NPK), N and P metabolism enzymes (nitrate reductase and phosphomonoesterase), photosynthetic pigments, chlorophyll fluorescence, sclerophylly and percentage cover of two common bryophytes (Pseudoscleropodium purum and Rhytidiadelphus squarrosus) to long-term (11 yr) enhanced N deposition (+3.5 and +14 g N m(-2) yr(-1)) are reported in factorial combination with P addition. Recovery of responses 22 months after treatment cessation were also assessed. Enhanced N deposition caused up to 90% loss of bryophyte cover but no recovery was observed. Phosphomonoesterase activity and tissue N:P ratios increased up to threefold in response to N loading and showed clear recovery, particularly in P. purum. Smaller responses and recovery were also seen in all chlorophyll fluorescence measurements and altered photosynthetic pigment composition. The P limitation of growth appears to be a key mechanism driving bryophyte loss along with damage to photosystem II. Physiological measurements are more sensitive than measurements of abundance as bioindicators of N deposition impact and of recovery in particular.     

Myco-heterotroph/epiparasitic plant interactions with ectomycorrhizal and arbuscular mycorrhizal fungi

More than 400 achlorophyllous plant species in 87 genera are parasitic upon fungi, and exploit them as their principle source of carbon. With a few exceptions, most of these myco-heterotrophic plants are now thought to be 'cheats', stealing carbon and nutrients from the mycorrhizal associates of adjacent autotrophic plants. Most myco-heterotrophs are therefore considered to be epiparasitic on green plants. Both the ectomycorrhizal and arbuscular mycorrhizal symbioses have been invaded by myco-heterotrophic epiparasites. DNA analysis is revealing the identities of many of the fungal partners of myco-heterotrophs, and their exceptionally high specificity. Myco-heterotrophs have distinctive stable isotope signatures, which can be used to establish the dependence upon fungal carbon of green plants that are partially myco-heterotrophic.     

Development,persistence and regeneration of foraging ectomycorrhizal mycelial systems in soil microcosms

Development of extraradical mycelia of two strains each of Paxillus involutus and Suillus bovinus in ectomycorrhizal association with Pinus sylvestris seedlings was studied in two dimensions in non-sterile soil microcosms. There were significant inter- and intra-specific differences in extraradical mycelial growth and morphology. The mycelial systems of both strains of P. involutus were diffuse and extended more rapidly than those of S. bovinus. Depending on the strain, P. involutus mycelia were either highly plane filled, with high mass fractal dimension (a measure of space filling) or sparse, low mass fractal dimension systems. Older mycelial systems persisted as linear cords interlinking ectomycorrhizal tips. S. bovinus produced either a mycelium with a mixture of mycelial cords and diffuse fans that rapidly filled explorable area, or a predominately corded mycelium of minimal area cover. In the soil microcosms, mass fractal dimension and mycelial cover tended to increase with time, mycelia encountering litter having significantly greater values. Results are discussed in terms of the ecology of these fungi, their foraging activities and functional importance in forest ecosystems.