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991.
The effects of ultraviolet-B radiation on regeneration after disturbance of a natural sub-arctic heathland have been investigated. Areas of pristine dwarf shrub heath were denuded of all above ground biomass in 1992 and exposed to enhanced UV-B (simulating a 15% depletion of the ozone layer). The resulting regenerated stem and leaf growth parameters were measured after four years on three dwarf shrubs, Vaccinium myrtillus, V. uliginosum and V. vitis-idaea and the grass Calamagrostis lapponica; leaves of the three dwarf shrubs were also analysed for UV-absorbing compounds and carbohydrates. Regeneration irrespective of treatment was slow, with Empetrum hermaphroditum failing to regenerate at all. Vaccinium myrtillus showed the most rapid regeneration attaining much of its original biomass in four years. There was a significant interaction between UV-B and year of regeneration in V. myrtillus; annual stem length increment showed an initial stimulation of 75% under enhanced UV-B in the first year of regeneration while a reduction of 16% was observed in the fourth year. Both V. uliginosum and V. vitis-idaea showed a reduction in annual stem length increment as regeneration progressed with a greater than 50% reduction in stem increment in the fourth year of regeneration compared to the first. Vaccinium uliginosum also showed an initial reduction in stem length increment of 40% under enhanced UV-B. None of the species were affected by enhanced UV-B in terms of total regenerated stem and leaf biomass or UV-absorbing compounds in regenerated leaf tissue. Total leaf carbohydrate and the ethanol/water soluble fraction in V. uliginosum were significantly increased by 29% and 31% respectively under enhanced UV-B. This suggests either a stimulation of photosynthesis or a reduction in sink size for photo-assimilates. Results are discussed in the context of the extremely slow regeneration of sub-arctic heath communities and the implications of contrasting UV-B effects on the regenerative ability of different species. 相似文献
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993.
Culturability of Mycobacterium tuberculosis cells isolated from murine macrophages: a bacterial growth factor promotes recovery 总被引:15,自引:0,他引:15
Biketov S Mukamolova GV Potapov V Gilenkov E Vostroknutova G Kell DB Young M Kaprelyants AS 《FEMS immunology and medical microbiology》2000,29(4):233-240
Very little is known about the culturability and viability of mycobacteria following their phagocytosis by macrophages. We therefore studied populations of the avirulent 'Academia' strain of Mycobacterium tuberculosis isolated from murine peritoneal macrophage lysates several days post-infection in vivo. The resulting bacterial suspensions contained a range of morphological types including rods, ovoid forms and coccoid forms. Bacterial viability measured using the MPN method (dilution to extinction in liquid medium) was often much higher than that measured by CFU (plating on solid medium). Viability in the MPN assay was further enhanced when the Micrococcus luteus protein, Rpf, was incorporated into the liquid culture medium at picomolar concentrations. Rpf is an example of a family of autocrine growth factors found throughout the high G+C cohort of Gram-positive bacteria including M. tuberculosis. M. tuberculosis cells obtained from macrophages had altered surface properties, as compared with bacteria grown in vitro. This was indicated by loss of the ability to adsorb bacteriophage DS6A, a reduced tendency to form clumps, acquisition of ethidium bromide stainability following heat treatment, and loss of Rpf-mediated resuscitation following freezing and thawing. These results indicate that a proportion of 'unculturable' M. tuberculosis cells obtained from macrophages is either injured or dormant and that these cells may be recovered or resuscitated using Rpf in liquid medium. 相似文献
994.
Anatomical and morphological characterization of mycorrhizas of five strains of Tuber borchii Vittad
G. Giomaro A. Zambonelli D. Sisti M. Cecchini V. Evangelista V. Stocchi 《Mycorrhiza》2000,10(3):107-114
Tilia platyphyllos Scop. plantlets were inoculated in vitro with five Tuber borchii Vittad. strains (1BO, 17BO, 43BO, 71BO and 10RA) to test their intraspecific variability. The ability of the strains to form
mycorrhizas varied, with the mean degree of ectomycorrhizal infection ranging from 50.6% (for 1BO) to 82.1% (for 10RA). The
anatomical/morphological characteristics of the resulting mycorrhizas were determined. Although the morphological features
of the mycorrhizas and the characteristics of the cystidia were similar for all strains tested, differences were found in
the anatomical features of the mantle. The form of the mantle cells was examined in the surface and inner layers (6 and 12 μm
deep, respectively) by both conventional and confocal microscopy. These cells were polygonal in 1BO, and 71BO, epidermoid
in 43BO and intermediate in 17BO and 10RA. The structure of the mantle also varied and thus provided little information with
which to identify T. borchii mycorrhizas.
Accepted: 7 July 2000 相似文献
995.
A general equation correlating the variation rate of the fermenting medium weight (dry matter) and the cell biomass growth
rate in solid-state fermentation tests is proposed with the main purpose of identifying the microbial growth phases.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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999.
神经生长因子制备工艺的改进及有关问题的讨论 总被引:1,自引:0,他引:1
为了达到规模化生产的目的 ,本文在神经生长因子制备工艺前增加了去脂处理 ,省略了CM (I)柱前的透析 ,并对影响生产收量的因素进行了探讨 ,使实验室结果得以有效放大 ,每 2 0 0 0对鼠颌下腺可提取蛋白 91mg ,总活性达 6 9× 10 7Bu。 相似文献
1000.