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281.
DONALD G. DUSANIC 《The Journal of eukaryotic microbiology》1968,15(2):328-333
SYNOPSIS. Culture forms of Trypanosoma lewisi grown at 27 C in a diphasic blood agar medium resemble in structure the stage found in the invertebrate host. Cultures inoculated with approximately 1 × 106 trypanosomes/ml attain maximum populations of 2–7 × 107 organisms/ml after 5–6 days of incubation. The stationary phase persists 6–15 days. The decline of the population is of relatively long duration with approximately 1 × 106 viable organisms/ml present after 90 days. Variations in growth were attributed to the preparation of defibrinated heated rabbit blood incorporated into the culture medium. With inocula of 3.0 × 105 trypanosomes/ml there was a lag in growth not observed with larger inocula. Trypanosomes incubated at elevated temperatures had altered growth curves compared to organisms at 27 C. Agitation of cultures did not affect the growth or stationary phases, but hastened the population decline. Heated and unheated 5% (v/v) normal rat serum incorporated in the liquid phase of the medium altered the growth of the organisms. Heated serum caused a decrease in the population and an extended lag phase. The effects on growth were more marked with unheated serum suggesting that both heat-stable and labile components affect growth. Antisera from rats injected with live culture forms included in the liquid phase inhibited, while antisera from rats 24 days after infection with the blood stream forms had no effect on the growth of the culture forms. Antisera from rabbits immunized with sonicates of culture forms also altered the growth of the organisms in culture. Rabbit antisera prepared by immunization with sonicates of dividing and non-dividing blood stream forms had no effect on the in vitro growth. Antisera from animals immunized with rat blood and culture medium were also without effect. The immunologic implications of the data are considered and discussed. 相似文献
282.
DONALD L. WISE 《The Journal of eukaryotic microbiology》1968,15(3):528-531
SYNOPSIS. Eight mM acetaldehyde prevented growth of Polytomella caeca in acetate medium and differentially changed the labeling by acetate-2-14C of chromatographically separated RNA hydrolysate products. Four mM acetaldehyde also prevented growth in acetate medium unless uridine, thymidine, guanosine, uracil, thymine or quanine were present; then growth was delayed by 2 or 4 days. Orotidine, orotic acid, dihydroortic acid, cytosine, cytidine, adenosine and adenine had no effect on growth in acetate medium containing 4 mM acetaldehyde. One mM acetaldehyde promoted growth in acetate medium and also could serve as a sole carbon source. One mM propionaldehyde, but not butyraldehyde, was also an adequate carbon source. Four mM acetaldehyde, as a sole carbon source, supported growth only when uridine was present. 相似文献
283.
Incubation of excised cucumber cotyledons (Cucumis sativus L.) with NH4Cl solutions exceeding 0.001 M inhibited their greening, fresh weight increases, and incorporation of 14C-leucine into insoluble N compounds. The absorption of 14C-leucine during incubation and retention of moisture by the excised cotyledons after incubation were greatly diminished by the NH4Cl treatments. Treatment with KCl solutions of the same concentrations as the NH4Cl stimulated the greening, fresh weight increases, and the absorption and incorporation of 14C-leucine. Desiccation of cotyledons stored at 5°C for 10 days was inhibited by dilute KCl solutions. The toxicity of NH4Cl was alleviated by KCl solutions at low concentrations. 相似文献
284.
Excision of the embryonic axis prior to 3 1/2 days of germination in the dark followed by 8-h of light decreased the total chlorophyll content of cucumber cotyledons but not squash cotyledons. Benzyladenine stimulated the accumulation of chlorophyll in the cotyledons of intact embryos and excised cotyledons in both cucumber and squash. Gibberellic acid had no effect. Atrazine inhibited chlorophyll formation in excised squash cotyledons. Benzyladenine also increased the carotenoid and xanthophyll content in the cotyledons from intact squash seedlings. The results suggest that pigment synthesis in cotyledons may be controlled by a number of substances produced in the embryonic axis and that cytokinin-like benzyladenine can simulate the action of one of them. 相似文献
285.
SYNOPSIS. Oocysts of Isospora marquardti sp. n. from the Colorado pika, Ochotona princeps , have spheroid oocysts, 30.5 (23–36) μm in diameter, and ovoid sporocysts, measuring 19.3 × 12.0 (17–22 × 10–14) μm. A polar body, 2 × 4 μm, a spheroid sporocyst residuum (8.3 μm in diameter), a Stieda body, and a distinct substiedal body (3 × 3 μm) are present. A micropyle and an oocyst residuum are absent. Excysted sporozoites, averaging 3.0 × 18.5 (2–4 × 15–20) μm, contain 2 refractile globules, 1 on each side of the nucleus with a prominent nucleolus.
The sporozoite excystation process using a trypsin-sodium taurocholate fluid is described. 相似文献
The sporozoite excystation process using a trypsin-sodium taurocholate fluid is described. 相似文献
286.
DONALD C. RHOADS JOHN W. MORSE 《Lethaia: An International Journal of Palaeontology and Stratigraphy》1971,4(4):413-428
Benthic invertebrates living in low oxygen regions of the Black Sea, Gulf of California, and basins off Southern California form three major biofacies associated with the following concentrations of dissolved oxygen: (1) an azoic region (≤ 0.1 ml/1), (2) a low diversity, small, soft-bodied infauna (0.3–1.0 ml/1), and (3) a diverse calcareous fauna (2 1.0 ml/l). These biofacies recapitulate the chronologic appearance of Pre-Cambrian trace fossils followed by a diverse calcified fauna in the Cambrian.
The basin model has been used to reconstruct a Lower Cambrian oxygen level of 0.1 P.A.L. (present atmospheric level). This value is ten-fold that proposed in the Berkner-Marshall hypothesis. 相似文献
The basin model has been used to reconstruct a Lower Cambrian oxygen level of 0.1 P.A.L. (present atmospheric level). This value is ten-fold that proposed in the Berkner-Marshall hypothesis. 相似文献
287.
DONALD L. PHILLIPS MARK G. JOHNSON DAVID T. TINGEY CHRISTINA E. CATRICALA† TONI L. HOYMAN† ROBERT S. NOWAK‡ 《Global Change Biology》2006,12(1):61-73
Fine roots (≤1 mm diameter) are critical in plant water and nutrient absorption, and it is important to understand how rising atmospheric CO2 will affect them as part of terrestrial ecosystem responses to global change. This study's objective was to determine the effects of elevated CO2 on production, mortality, and standing crops of fine root length over 2 years in a free‐air CO2 enrichment (FACE) facility in the Mojave Desert of southern Nevada, USA. Three replicate 25 m diameter FACE rings were maintained at ambient (~370 μmol mol?1) and elevated CO2 (~550 μmol mol?1) atmospheric concentrations. Twenty‐eight minirhizotron tubes were placed in each ring to sample three microsite locations: evergreen Larrea shrubs, drought‐deciduous Ambrosia shrubs, and along systematic community transects (primarily in shrub interspaces which account for ~85% of the area). Seasonal dynamics were similar for ambient and elevated CO2: fine root production peaked in April–June, with peak standing crop occurring about 1 month later, and peak mortality occurring during the hot summer months, with higher values for all three measures in a wet year compared with a dry year. Fine root standing crop, production, and mortality were not significantly different between treatments except standing crop along community transects, where fine root length was significantly lower in elevated CO2. Fine root turnover (annual cumulative mortality/mean standing crop) ranged from 2.33 to 3.17 year?1, and was not significantly different among CO2 treatments, except for community transect tubes where it was significantly lower for elevated CO2. There were no differences in fine root responses to CO2 between evergreen (Larrea) and drought‐deciduous (Ambrosia) shrubs. Combined with observations of increased leaf‐level water‐use efficiency and lack of soil moisture differences, these results suggest that under elevated CO2 conditions, reduced root systems (compared with ambient CO2) appear sufficient to provide resources for modest aboveground production increases across the community, but in more fertile shrub microsites, fine root systems of comparable size with those in ambient CO2 were required to support the greater aboveground production increases. For community transects, development of the difference in fine root standing crops occurred primarily through lower stimulation of fine root production in the elevated CO2 treatment during periods of high water availability. 相似文献
288.
PAUL F. DONALD LYS B. MUIRHEAD DAVID L. BUCKINGHAM REW D. EVANS WILL B. KIRBY DEREK J. GRUAR 《Ibis》2001,143(3):658-669
Factors affecting the diet, body condition and growth rates of Skylark chicks were assessed to examine their relationship to their agricultural environment during a critical period in the life cycle of this rapidly declining species. Rainfall explained the greatest amount of variation in body condition and growth rates and had a negative effect on both. Body condition indices were a good predictor of the likelihood of future partial brood loss to starvation. Low body condition in grass fields was related to a low diversity in the diet. Chicks fed insect larvae had higher body condition indices than those not fed larvae. Larger broods tended to have higher growth rates than smaller ones, whereas smaller broods tended to have higher body condition indices. Natural brood size reduction through the non-hatching of eggs resulted in higher body condition indices than were found in nests with the same number of chicks where all eggs hatched, this effect being independent of absolute brood size. There was no significant difference between crop types in the distance adult birds flew to forage for food for nestlings and foraging crop destination had no effect on chick development. Differences between crop types in chick diet could be related to the documented effects of pesticides on different prey species. We suggest that recent agricultural changes have affected diet and possibly body condition, but that these effects are unlikely to have been an important factor in recent population declines. 相似文献
289.
290.