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161.
STUART S. BAMFORTH 《The Journal of eukaryotic microbiology》1985,32(3):404-409
Soil is the focus of organic matter turnover in terrestrial ecosystems and is an interstitial mosaic of microsites composed of particle aggregates and pore spaces, where transformation, decomposition, mineralization, and humification of organic matter takes place. Microorganisms and animals are scattered discontinuously in these microsites. Microarthropods and larger fauna increase the rate and amount of mineralization by comminution of organic matter and by redistribution of microsites through movements of earthworms and large arthropods; however, mineralization and return of nutrients to plants occurs in the community of bacteria, fungi, protozoa, and nematodes living in the water films covering aggregates and filling pore spaces. Protozoa, especially small amoebae, are important bacterial grazers because they can enter tiny spaces unavailable to nematodes. The latter graze bacteria, fungi, and protozoa. Protozoan and nematode predation increase the amounts of soluble nutrients and decrease the competitive abilities of bacteria, thus making these nutrients more available to plants. Protozoa enhance nutrient recycling out of proportion to their biomass. 相似文献
162.
Two-dimensional polyacrylamide gel electrophoresis has been used to analyze changes in protein content and protein synthesis in three stages of the life cycle of the protozoan parasite Trypanosoma brucei. The stages examined were slender and stumpy mammalian bloodstream forms and procyclic forms, which are analogous to the tsetse fly midgut stage. Two-dimensional gels of 35S-methionine-labeled proteins were examined by autoradiography to analyze newly synthesized protein, and gels were stained with ammoniacal silver to analyze proteins present. Several stage-specific molecules were noted. The most obvious was the variant surface glycoprotein, which was only present in bloodstream forms. Some other proteins were also bloodstream form specific; they had molecular weights of 120,000 and 38,000. Proteins of 52,000, 46,000, 25–30,000, and 16,000 daltons were present both in stumpy forms and procyclics but not in slender-form trypanosomes. Several proteins (molecular weights of 50–70,000, 43,000, 40,000, 26–24,000, 20–25,000, and 15,000) were present only in one of the three stages. One protein, a molecule of about 18,000 daltons present in both slender and stumpy parasites, did not appear to be synthesized in the stumpy stage. In vitro translation products of mRNA purified from the three stages were also examined. The abundance of mRNA encoding a protein of about 40,000 daltons appeared to be greater in slender than in stumpy parasites although the stumpy forms contained more of the protein and synthesized it at a higher rate. 相似文献
163.
BRADLEY STUART LAW 《Austral ecology》1994,19(4):366-374
Abstract This study investigates the importance of climate as a factor influencing the southern distributional limit of the common blossom bat (Syconycteris australis). Using the climatic predictive model BIOCLIM and 73 locality records, 5. australis was predicted to have a coastal distribution in eastern Australia, where winter temperatures are relatively warm and moist conditions prevail throughout the year. The actual southern limit of S. australis, determined by mist-netting suitable habitats, was found to be at Booti-Booti (32°19'S 152°3l'E) on the mid-north coast of New South Wales. BIOCLIM predicted the southerly limit of 5. australis to be 150–200km further south of their actual limit. Booti-Booti was occupied at relatively low levels of abundance year round, while the abundance of S. australis at a site 50 km to the north was much greater, fluctuating with changes in Banksia flower numbers. Seasonal range extensions beyond Booti-Booti were not detected, despite the availability of apparently suitable habitat at Myall Lakes only 20–35 km further south. Metabolic costs of S. australis at Booti-Booti were estimated to exceed basal metabolic rate (BMR) by 4.5 times, well above the physiologically predicted limit of 2.5 times BMR. These results, together with the lack of range extensions and the close correspondence of BIOCLIM'S predicted southern limit of S. australis with their actual limit, suggest that the bat's southern distribution is limited by cold, wet winters and dry summers. 相似文献
164.
Generic revision of the New World tribe Hoplophorionini (Hemiptera: Membracidae: Membracinae) 总被引:2,自引:0,他引:2
Abstract. The tribe Hoplophorionini Goding, 1926, includes 105 species of treehoppers in 10 genera. All are apparently subsocial and lack mutualism with honeydew-collecting hymenopterans. In many species, parental investment in offspring is unique because of a specialized kicking defence (described herein) and construction of extra-ovipositional punctures in the host tissue through which nymphs feed. The tribe occurs from Canada to Chile, with most generic diversity in Central America but most species diversity near the equator. Three genera, Stalotypa Metcalf, Ramosella, new genus and Stirpis, new genus, are endemic to the Greater Antilles but do not constitute a monophyletic group; the first two genera appear most closely related to Turrialbia, new genus, from Costa Rica. Host plant specializations and other biological attributes are summarized for genera and species. A phylogenetic analysis of 23 hoplophorionine species produced 9 minimal-length cladograms that were similar in many respects. Potnia Stål appears to have retained the greatest number of ancestral features. Aposematic teneral coloration of adults probably evolved once. The modification of the ancestral kicking behaviour by the first hoplophorionines appears to have released them from a constraint on pronotal form. Diagnoses are given for adults of all genera and, when possible, for immatures. A key is presented for the 10 genera; three are described as New Genera based on the cladistic analysis: Ramosella, Stirpis, and Turrialbia. Three New Species are described: Ramosella thalli, Stirpis jamaicensis, and Turrialbia felina. The genus Micropepla Sakakibara is considered a junior synonym of Ochropepla Stal, New Generic Synonymy. Umbonia terribilis Walker is moved from synonymy under Alchisme virescens (Fairmaire) to a New Synonymy under Umbonia reducta Walker. The subspecies Platycotis vittata vittata (Fabricius), P. vittata lineata (Fairmaire), and P. vittata quadrivittata (Say) are returned to synonymy with Platycotis vittata (Fabricius), Reinstated Specific Synonymies. Three species are Reinstated as valid: Alchisme obscura (Walker) and A. veruta (Fowler), both from synonymy under A. turrita (Germar); and Umbonia reducta Walker, from synonymy under U. crassicomis (Amyot & Serville). Five New Combinations are proposed: Alchisme antigua (Funkhouser), referred from Umbonia; A. sordida (Germar), referred from Platycotis; A. sagittata (Germar), elevated from subspecific rank under Platycotis vittata; Ochropepla mourei (Sakakibara), referred from Micropepla; and Ramosella dominicensis (Ramos), referred from Platycotis. Platycotis nigrorufa (Walker), P. cornuta Plummer, P. salvini (Fowler), and P. fuscata (Fowler) were previously unplaced to subgenus; the first is referred to Platycotis (Lophopelta Stal) and the others to Platycotis (Platycotis Stål). Microschaema nigrostrigata Buckton is moved from synonymy under Alchisme recurva (Stål) to a New Synonymy under Ennya dorsalis (Fairmaire) of the tribe Polyglyptini, subfamily Smiliinae. A checklist with critical synonymies and indexes to hoplophorionine taxa and host plant associations are provided. Lectotypes are designated for Centrotus vittatus Fabricius, Hoplophora lineata Fairmaire, Membracis venosa Germar, Potnia affinis Buckton, and Triquetra obtusa Fowler. 相似文献
165.
ABSTRACT. Phosphorylation of proteins at tyrosine is an important mechanism for regulating cell growth and proliferation in metazoan organisms. In this report, we have demonstrated that Trypanosoma brucei , a protozoan parasite, possesses a tyrosine kinase that plays a role in regulation of proliferation of this protozoan. Genistein, a tyrosine kinase inhibitor, prevented multiplication of the parasite. An in vitro kinase assay demonstrated the presence of a kinase capable of phosphorylating an exogenous substrate at tyrosine, and genistein was able to reduce trypanosome-mediated phosphorylation of this substrate. An alkali digestion of 32 P-labeled trypanosome proteins separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicated several proteins phosphorylated at tyrosine. These results indicate that T. brucei has a tyrosine kinase that is involved in proliferation or growth regulation of the parasite and provide further evidence for the possibility of growth factor regulation and signal transduction in trypanosomes. 相似文献
166.
TZUHUA LIN JUKKA PAJARINEN YUSUKE KOHNO MASAHIRO MARUYAMA MONICA ROMERO-LOPEZ JHIH-FONG HUANG KARTHIK NATHAN TAHSIN N. KHAN ZHENYU YAO STUART B. GOODMAN 《Cytotherapy》2018,20(8):1028-1036
Background
Mesenchymal stromal cell (MSC)–based therapy has great potential to modulate chronic inflammation and enhance tissue regeneration. Crosstalk between MSC-lineage cells and polarized macrophages is critical for bone formation and remodeling in inflammatory bone diseases. However, the translational application of this interaction is limited by the short-term viability of MSCs after cell transplantation.Methods
Three types of genetically modified (GM) MSCs were created: (1) luciferase-expressing reporter MSCs; (2) MSCs that secrete interleukin (IL)-4 either constitutively; and (3) MSCs that secrete IL-4 as a response to nuclear factor kappa-light-chain-enhancer of activated B cell (NFκB) activation. Cells were injected into the murine distal femoral bone marrow cavity. MSC viability and bone formation were examined in vivo. Cytokine secretion was determined in a femoral explant organ culture model.Results
The reporter MSCs survived up to 4 weeks post-implantation. No difference in the number of viable cells was found between high (2.5?×?106) and low (0.5?×?106) cell-injected groups. Injection of 2.5?×?106 reporter MSCs increased local bone mineral density at 4 weeks post-implantation. Injection of 0.5?×?106 constitutive IL-4 or NFκB-sensing IL-4–secreting MSCs increased bone mineral density at 2 weeks post-implantation. In the femoral explant organ culture model, LPS treatment induced IL-4 secretion in the NFκB-sensing IL-4–secreting MSC group and IL-10 secretion in all the femur samples. No significant differences in tumor necrosis factor (TNF)α and IL-1β secretion were observed between the MSC-transplanted and control groups in the explant culture.Discussion
Transplanted GM MSCs demonstrated prolonged cell viability when transplanted to a compatible niche within the bone marrow cavity. GM IL-4–secreting MSCs may have great potential to enhance bone regeneration in disorders associated with chronic inflammation. 相似文献167.
When reared at high densities, young Helix aspersa show lessshell growth, even if waste products are removed. They alsofeed less, and show increased mortality. It is suggested thatthese effects are linked to reduced activity. Juveniles showreduced activity in the presence of adults or their mucus. Mucusof adult Cepaca nemoralis also depresses the activity of bothadult and young Helix and Cepaea.
* Present Address: Unit Zoologi, Universiti Kebangsaan Malaysia,Jalan Pantai Baru, Kuala Lumpur, West Malaysia. (Received 12 May 1981; 相似文献
168.
STUART H. HURLBERT 《Austral ecology》1997,22(4):369-382
Abstract Two concepts relating to the influence of individual species on the biocenoses in which they occur are reviewed. The first, the general functional importance of a species, is denned as the sum, over all species, of the changes (sign ignored) in productivity which would occur on removal of the particular species from the biocenosis. General functional importance is calculated as: where Pj is the productivity of the jth species before (t= 0) and after (t= 1) removal of the particular (ith) species being evaluated. Though Ii values cannot be determined empirically, this concept raises provocative questions for theoretical biocenology. The second concept reviewed is that of the keystone species. Never having been precisely or operationally defined,‘keystone’ has come to mean little more than ‘important for something.’ Moreover, there is no empirical or theoretical foundation for the idea that there exists in any biocenosis a natural dichotomy corresponding to the verbal one of keystone and non-keystone species. Some investigators have implied that such a dichotomy is suggested by the frequency distributions of experimentally determined values of interaction strength. The patterns they refer to are, however, artifacts resulting from small sample sizes and the plotting of frequency distributions on arithmetic rather than logarithmic scales. As a casual metaphor ‘keystone species’ was appealing and harmless; but the pretence that it is a well-defined concept or phenomenon has had a stultifying effect on ecological thought and argument. 相似文献
169.
Markov chain models for threshold exceedances 总被引:7,自引:0,他引:7
170.
PETER A. NYBERG DIANA H. BAUER and STUART E. KNAPP 《The Journal of eukaryotic microbiology》1968,15(1):144-148
SYNOPSIS. The stimulus necessary to initiate in vitro excystation of the chicken coccidium Eimeria tenella was provided by exposure of intact sporulated oocysts to an atmosphere of carbon dioxide. This stimulus produced a thinning and indentation at the micropylar region and oocysts became permeable to trypsin and bile. Sporozoites became active and began to escape from sporocysts into the oocyst cavity and then to the outside thru the altered micropyle after incubation in the enzyme-bile mixture. Activation of sporozoites when CO2-pretreated oocysts were incubated in trypsin and bile, was used as the criterion to determine the number of oocysts responding to the initial stimulus. Thus, activation of sporozoites within intact oocysts was an indirect measurement of the number of oocysts stimulated during CO2-pretreatment. Approximately 90% of the oocysts contained active sporozoites after 18 hr of pretreatment with carbon dioxide and 8 hr incubation in trypsin and bile at 38 or 41 C, respectively. Pretreatment of oocysts with air, N2, O2, or He resulted in 8% or less activation during incubation in trypsin and bile. Approximately 83% of the oocysts responded to the stimulus during 8 hr CO2-pretreatment at 41 C, whereas at 38 C, 16 hr of pretreatment were required for a similar response. The stimulus did not elicit a response from oocysts held at 23 C during the pretreatment gasphase. No significant difference occurred in number of oocysts containing active sporozoites after sufficient CO2-pretreatment for maximum stimulation of oocysts and incubation in trypsin and bile at 38 or 41 C. 相似文献