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201.
Results of a 7-yr field study and a 3-yr slaughterhouse study into reproductive performance and reproductive wastage of ruminants in central Mali are reported. Cattle had delayed age at first puberty (40), long calving intervals (644) and produced few young (3.02) per lifetime. Goats and sheep first conceived at about 11 mo, had shorter parturition intervals (298 and 280 d) but also produced few young (2.64 and 1.92) per lifetime. Conceptions showed a strong seasonality in cattle and mainly occurred during and shortly after the short rainy season. Seasonality was less marked in small ruminants, but most females conceived before the rains. However, maximum litter sizes were associated with late-rain and post-rain conceptions. Early embryonic wastage did not appear to be a major problem but abortions, stillbirths and heavy preweaning mortality were sources of loss of reproductive potential. Additionally at a secondary (government controlled) abattoir, 15.0 % of cows, 31.7 % of goats and 20.0 % of sheep that were slaughtered were found to be pregnant. 相似文献
202.
Thirty-seven bacteriophages plaquing on Corynebacterium, Brevibacterium, or Arthrobacter strains were isolated from soil or vegetation samples. Restriction analysis of phage DNA indicated that 20 phages were unique; one of them produced entirely turbid plaques on Brevibacterium ketoglutamicum and was characterized as temperate. All these phages were assigned to group B of the classification of Bradley (Bacteriol. Rev. 31:230-314, 1967) and had relatively narrow host ranges. 相似文献
203.
The steady-state effect of 2,5,2',5'-tetrachlorobiphenyl (TCBP) on the green alga Selenastrum capricornutum was investigated in a P-limited two-stage chemostat system. The partition coefficient of this polychlorinated biphenyl congener was 5.9 x 10 in steady-state cultures. At a cellular TCBP concentration of 12.2 x 10 ng . cell, growth rate was not affected. However, photosynthetic capacity (P(max)) was significantly enhanced by TCBP (56 x 10 mumol of C . cell . h versus 34 x 10 mumol of C . cell . h in the control). Photosynthetic efficiency, or the slope of the photosynthesis-irradiance curve, was also significantly higher. There was little difference in the cell chlorophyll a content, and therefore the difference in these photosynthetic characteristics was the same even when they were expressed on a per-chlorophyll a basis. Cell C content was higher in TCBP-containing cells than in TCBP-free cells, but approximately 36% of the C fixed by cells with TCBP was not incorporated as cell C. The maximum P uptake rate was also enhanced by TCBP, but the half-saturation concentration appeared to be unaffected. 相似文献
204.
Semen and blood samples from 154 rams from two Montana range flocks (Flock A, vaccinated for Brucella ovis ; Flock B, nonvaccinated) were evaluated to determine the relationship between Brucella ovis (B. ovis ) semen culture results and various semen and blood parameters. All rams utilized in this study exhibited no palpable ram epididymitis lesions. Thirteen and 25.6% of the rams tested in Flocks A and B, respectively, had positive B. ovis semen cultures. Only age of ram and ram condition scores differed (P<0.05) between flocks. No flock by semen culture interactions were detected (P>0.05) for any of the parameters evaluated. Age of ram, ram condition score, and spermatozoa rate from forward movement were unrelated (P>0.05) to B. ovis culture results. Rams with positive B. ovis semen cultures had lower sperm motility (P<0.05), higher percentage of abnormal spermatozoa cells (P<0.05), higher percentage of spermatozoa head abnormalities (P<0.01), lower percentage of live-normal cells (P<0.05), higher incidence of white blood cells in semen (P<0.01) and higher complement fixation (CF) titers (P<0.01). 相似文献
205.
洞穴生物生活在地下。地下栖息场所最主要的特点是永远处于黑暗中,无自养生物,食物的种类和数量非常贫乏。当然,栖息地的大小以及其他非生物特征各有不同。来自地表食物极少的碎石间的空隙,也属于地下栖息地。但最主要的是喀斯特洞穴,尤其是在石灰岩地区形成的洞穴。溶岩流中的溶岩隧道是一类特殊 相似文献
206.
Metal Ion Interactions with Phosphoenolpyruvate Carboxylase from Crassula argentea and Zea mays 总被引:1,自引:1,他引:0
Metal ion interactions with phosphoenolpyruvate carboxylase from the CAM plant Crassula argentea and the C4 plant Zea mays were kinetically analyzed. Fe2+ and Cd2+ were found to be active metal cofactors along with the previously known active metals Mg2+, Mn2+, and Co2+. In studies with the Crassula enzyme, Mg2+ yielded the highest Vmax value but also generated the highest values of Km(metal) and Km(pep). For these five active metals lower Km(metal) values tended to be associated with lower Km(pep) values. PEP saturation curves showed more kinetic cooperativity than the corresponding metal saturation curves. The activating metal ions all have ionic radii in the range of 0.86 to 1.09 Å. Ca2+, Sr2+, Ba2+, and Ni2+ inhibited competitively with respect to Mg2+, whereas Be2+, Cu2+, Zn2+, and Pd2+ showed mixed-type inhibition. Vmax trends with the five active metals were similar for the C. argentea and Z. mays enzymes except that Cd2+ was less effective with the maize enzyme. Km(metal) values were 10- to 60-fold higher in the enzyme from Z. mays. 相似文献
207.
In the seeds of Hevea brasiliensis, the cyanogenic monoglucoside linamarin (2-β-d-glucopyranosyloxy-2-methylpropionitrile) is accumulated in the endosperm. After onset of germination, the cyanogenic diglucoside linustatin (2-[6-β-d-glucosyl-β-d-glucopyranosyloxy]-2- methylpropionitrile) is formed and exuded from the endosperm of Hevea seedlings. At the same time the content of cyanogenic monoglucosides decreases. The linustatin-splitting diglucosidase and the β-cyanoalanine synthase that assimilates HCN, exhibit their highest activities in the young seedling at this time. Based on these observations the following pathway for the in vivo mobilization and metabolism of cyanogenic glucosides is proposed: storage of monoglucosides (in the endosperm)—glucosylation—transport of the diglucoside (out of the endosperm into the seedling)—cleavage by diglucosidase—reassimilation of HCN to noncyanogenic compounds. The presence of this pathway demonstrates that cyanogenic glucosides, typical secondary plant products serve in the metabolism of developing plants as N-storage compounds and do not exclusively exhibit protective functions due to their repellent effect. 相似文献
208.
Metabolic Acclimation to Anoxia Induced by Low (2-4 kPa Partial Pressure) Oxygen Pretreatment (Hypoxia) in Root Tips of Zea mays 总被引:10,自引:7,他引:3
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Young intact plants of maize (Zea mays L. cv INRA 508) were exposed to 2 to 4 kilopascals partial pressure oxygen (hypoxic pretreatment) for 18 hours before excision of the 5 millimeter root apex and treatment with strictly anaerobic conditions (anoxia). Hypoxic acclimation gave rise to larger amounts of ATP, to larger ATP/ADP and adenylate energy charge ratios, and to higher rates of ethanol production when excised root tips were subsequently made anaerobic, compared with root tips transferred directly from aerobic to anaerobic media. Improved energy metabolism following hypoxic pretreatment was associated with increased activity of alcohol dehydrogenase (ADH), and induction of ADH-2 isozymes. Roots of Adh1− mutant plants lacked constitutive ADH and only slowly produced ethanol when made anaerobic. Those that were hypoxically pretreated acclimated to anoxia with induction of ADH2 and a higher energy metabolism, and a rate of ethanol production comparable to that of nonmutants. All these responses were insensitive to the presence or absence of NO3−. Additionally, the rate of ethanol production was about 50 times greater than the rate of reduction of NO3− to NO2−. These results indicate that nitrate reductase does not compete effectively with ADH for NADH, or contribute to energy metabolism during anaerobic respiration in this tissue through nitrate reduction. Unacclimated root tips of wild type and Adhl− mutants appeared not to survive more than 8 to 9 hours in strict anoxia; when hypoxically pretreated they tolerated periods under anoxia in excess of 22 hours. 相似文献
209.
Senescence-specific increase in cytosolic glutamine synthetase and its mRNA in radish cotyledons 总被引:11,自引:4,他引:7
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Changes in the levels of cytosolic and chloroplastic isoforms of glutamine synthetase were examined in senescing radish (Raphanus sativus L. cv Comet) cotyledons by immunoblotting analysis using antibodies raised separately against maize glutamine synthetase isoforms. Translatable mRNAs for these isoforms were also examined by analyzing translation products from poly(A)+ RNA in a wheat germ system with the antibodies. The relative content of cytosolic isoform (GS1) increased twofold in the cotyledons that were placed in the dark for 72 hours to accelerate senescence, while that of chloroplastic isoform (GS2) declined to half of its initial level. The dark-treatment also increased the relative level of translatable mRNA for GS1 sevenfold after 72 hours, and decreased rapidly that for GS2 and for other nuclear-coded chloroplast proteins as well. Cotyledons also accumulated GS1 mRNA when they became senescent after a lengthy growth period under continuous light. These observations suggested that GS1 genes were activated, while those for GS2 were repressed, and eventually the population of the enzyme was altered in senescent cotyledonary cells. The role of increased cytosolic enzyme is discussed in relation to the nitrogen metabolism in senescent leaves. 相似文献
210.
l-Glutamate-Dependent Medium Alkalinization by Asparagus Mesophyll Cells : Cotransport or Metabolism?
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Mechanically isolated Asparagus sprengeri Regel mesophyll cells cause alkalinization of the suspension medium on the addition of l-glutamate or its analog l-methionine-d,l-sulfoximine. Using a radiolabeled pH probe, it was found that both compounds caused internal acidification whereas l-aspartate did not. Fusicoccin stimulated H+ efflux from the cells by 111% and the uptake of l-[U-14C]glutamate by 55%. Manometric experiments demonstrated that, unlike l-methionine-d,l-sulfoximine, l-glutamate stimulated CO2 evolution from nonilluminated cells. Simultaneous measurements of medium alkalinization and 14CO2 evolution upon the addition of labeled l-glutamate showed that alkalinization was immediate and reached a maximum value after 45 minutes whereas 14CO2 evolution exhibited a lag before its appearance and continued in a linear manner for at least 100 minutes. Rates of alkalinization and uptake of l-[U-14C]glutamate were higher in the light while rates of 14CO2 evolution were higher in the dark. The major labeled product of glutamate decarboxylation, γ-aminobutyric acid, was found in the cells and the suspension medium. Its addition to the cell suspension did not result in medium alkalinization and evidence indicates that it is lost from the cell to the medium. The data suggest that the origin of medium alkalinization is co-transport not metabolism, and that the loss of labeled CO2 and γ-aminobutyric acid from the cell result in an overestimation of the stoichiometry of the H+/l-glutamate uptake process. 相似文献