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101.
102.
Vegetation change over a nine-year period was studied in Guadalupe Mountains, New Mexico. Permanent transects in desert shrub
vegetation were sampled in 1972 and 1980. Emphasis was given to shrubs because of their importance to big game diets. Univariate
paired t-tests and reciprocal averaging ordination were used to detect and display coordinated changes in species composition over
time. Despite apparently less browsing pressure in desert shrub vegetation in 1980 there were few significant changes in species
composition. In addition, preferred forage species showed reduced reproduction while species of intermediate and poor forage
value dis-played increased reproduction during this time. These data do not support traditional rangeland succession theory
which states that enhanced reproduction of preferred species should follow grazing or browsing pressure reduction. 相似文献
103.
Summary The nuclear DNA content of cotyledonary cells of two lupin seeds (L1 and L2) with markedly different total protein content, were investigated by scanning cytophotometry. Both seeds had polyloid nuclei with DNA levels varying between 8 C and 64 C, the majority being either 16 C or 32 C. The highest DNA levels were found in the abaxial and central cotyledonary zones of both seeds; seed L2 had a higher ploidy level than L1. It is shown that the volume of condensed chromatin (chromocenters) increased proportionally with the DNA content of the nucleus. A comparison was made between the distribution of protein, previously determined byLe Gal andRey (1986) and the DNA throughout the cotyledon. The L2 seed, which has the highest total protein and the highest protein content per cell, also exhibited the greatest DNA content per cell. For both seeds, the r-value for association of DNA and protein content per cell was highly significant (0.98). 相似文献
104.
An epidemiological survey of the vectors of cutaneous leishmaniasis ("espúndia" type) was carried out in the Alto Beni region of Bolivia, an area of Andean foothills at the Eastern limit of the Amazonian lowlands. The climate is typical wet tropical (15 degrees S latitude). Anthropophilic phlebotomine sandfly species were sampled at 20 sites, all forested. The importance of species from the Psychodopygus group, already suspected as a vector in the transmission of Leishmania from the braziliensis complex, was confirmed by: the aggressiveness and diversity of the species encountered (83% of catches, nine species), the discovery of a new anthropophilic species, P. yucumensis and the isolation of a strain of Leishmania braziliensis braziliensis indistinguishable from human strains from the same area, from two species, P. llanosmartinsi and P. yucumensis. 相似文献
105.
Ammonium release by zooplankton in suspensions of heat-killed algae and an evaluation of the flow-cell method 总被引:1,自引:0,他引:1
Vanderploeg Henry A.; Laird Gwenyth A.; Liebig James R.; Gardner Wayne S. 《Journal of plankton research》1986,8(2):341-352
The maximum excretion rate of NH4 (39 nmol mg dry wt1h1) was directly measured for Daphnia pulex by measuringNH4 accumulation in bottles containing D. pulex and dense, satiatingsuspensions of heat-killed algae. Ammonium release rates inthe algal suspensions were compared to those of individual animalsremoved from the suspension and placed in flow cells. Ammoniumrelease rate, R (nmol mg dry wt1 h1). in the flowcell decreased very rapidly with time, t (min), after removalaccording to the relation R = 26 + 25e0.16t. Ammoniumexcretion obtained by the flow cell method after extrapolationto time zero was not significantly different from that obtainedin the bottles. The considerable experiment-to-experiment variationin NH4 excretion was in large part correlated (r2 = 0.73) withthe feeding rate on the algae. 相似文献
106.
Y Le Parco J P Cecchini B Knibiehler C Mirre 《Biology of the cell / under the auspices of the European Cell Biology Organization》1986,56(3):217-226
We have used a cloned chicken collagen cDNA sequence to help identify hypothetic members of the collagen gene family from Drosophila melanogaster. Several experimental evidences have been obtained which indicate that the Drosophila genome contains numerous collagen-like sequences. We have characterized in more detail ten distinct DNA sequences that hybridized strongly to the heterologous collagen probe. By in situ hybridization we have shown that these sequences are dispersed throughout the Drosophila genome. Two of them are shown to originate from the previously described DCg 1 and DCg 2 collagen genes. In other respects, we show that in addition to DCg 1 and DCg 2, at least five putative collagen genes are expressed during the Drosophila lifetime. These genes are unique, and some of them are seen to be transcribed into different size classes of mRNAs. Additionally, the data presented so far demonstrate that the expression of these genes is regulated temporally and/or quantitatively during the Drosophila life cycle. 相似文献
107.
Summary Chromaffin granules from bovine adrenal medullary chromaffin cells have been found to contain small vesicular structures bounded by unit membranes. Detection of these intragranular vesicles within intact cells requires the use of quick-freezing methods. The intragranular vesicles are labile to fixation by aldehydes which explains why they have not been described in intact cells until now. They are found in approximately 60% of the dense-core chromaffin granules in cells and 85% of isolated granules. They are usually clustered in groups of one to as many as five between the core and the inner surface of the granule membrane. The intragranular vesicles are independent vesicles in that they do not appear as simple invaginations of the granule membrane in either serial thin-section or freeze-etch views. Furthermore, they are released from the cell along with granule contents during nicotine-induced secretion of catecholamines. The structural heterogeneity provided by the intragranular vesicles may be related to the functional heterogeneity of granule contents observed in many recent biochemical studies. 相似文献
108.
The proα2 (V) collagen gene (COL5A2) maps to 2q14→2q32, syntenic to the proα1 (III) collagen locus (COL3A1) 总被引:3,自引:0,他引:3
Cécile Huerre-Jeanpierre Isabelle Henry M. Bernard Pia Gallano Dominique Weil K. H. Grzeschik F. Ramirez Claudine Junien 《Human genetics》1986,73(1):64-67
Summary A recombinant probe specific for the pro2 chain of human Type V collagen has been used for the localization of the corresponding gene (COL5A2) to chromosome 2. Regional mapping by in situ hybridization and analysis of DNA from humanxrodent cell lines indicated that COL5A2 is confined within the segment 2q142q32, thus syntenic to the pro1 (III) collagen gene (COL3A1). 相似文献
109.
Cloning structural gene sacB, which codes for exoenzyme levansucrase of Bacillus subtilis: expression of the gene in Escherichia coli. 总被引:17,自引:10,他引:7
A clone bearing the structural gene sacB, coding for the exoenzyme levansucrase, was isolated from a library of Bacillus subtilis DNA that was cloned in phage lambda charon 4A on the basis of the transforming activity of the chimeric DNA. This lambda clone also was found to contain the sacR and smo loci. Subcloning the sacB-sacR region in plasmid pBR325 resulted in a clone which directed levansucrase synthesis in Escherichia coli. The nucleotide sequence coding for the secreted protein was localized on the physical map of the cloned DNA. 相似文献
110.
N Le Trant S R Meshnick K Kitchener J W Eaton A Cerami 《The Journal of biological chemistry》1983,258(1):125-130
Leishmania tropica, Trypanosoma brucei, Trypanosoma cruzi, and Crithidia fasciculata have superoxide dismutases which are insensitive to cyanide and sensitive to peroxide and azide, properties characteristic of iron-containing superoxide dismutase. Studies on the superoxide dismutase of C. fasciculata have revealed that: 1) the enzyme is located in the cytosol; 2) isozymes exist; 3) the major superoxide dismutase isozyme (superoxide dismutase 2) has Mr approximately equal to 43,000 and consists of two equal-sized subunits, each of which contains 1.4 atoms of iron. Comparisons of the amino acid content of this crithidial superoxide dismutase with those of superoxide dismutases from other sources suggests that the crithidial enzyme is closely related to bacterial Fe-containing superoxide dismutases, and only distantly related to human Mn- and Cu,Zn-containing superoxide dismutases and to Euglena Fe-containing superoxide dismutase. Attempts are now underway to develop specific inhibitors of the trypanosomatid superoxide dismutase which may be of use in the treatment of leishmaniasis or trypanosomiasis. 相似文献