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1.
Genetically modified tobacco plants (Nicotiana tabacumSamsun)with antisense cinnamyl alcohol dehydrogenase DNA, produce secondaryxylem of a reduced tensile stiffness. These plants were grownalongside control plants. The stems of the plants were flexedor protected from flexing over a period of several weeks. Thetensile moduli and second moments of areas of the differenttissues inside the stems were measured and used to calculatethe bending stiffness of the plants. In tobacco, the cylinderof xylem was found to be the most important tissue in determiningthe bending stiffness of the plants. The thickness of the xylemtissue cylinder increased when plants were subjected to flexuralstimulation. This increased the bending stiffness of the stems.The response to mechanical stimulation was found to be correlatedwith tissue strain and the genetically modified plants wereable to exactly compensate for the reduced modulus of theirxylem tissue by increasing the thickness of the xylem tissuecylinder more than in control plants.Copyright 1999 Annals ofBotany Company. Tobacco plants, stem bending, xylem tissue, second moment of area, thigmomorphogenesis, mechanical strain. 相似文献
2.
ELISA absorbance cut-off method affects malaria sporozoite rate determination in wild Afrotropical Anopheles 总被引:1,自引:0,他引:1
JOHN C. BEIER CHARLES M. ASIAGO FRED K. ONYANGO JOSEPH K. KOROS 《Medical and veterinary entomology》1988,2(3):259-264
ABSTRACT. Malaria sporozoite infection rates in a mixed species group of 244 Anopheles gambiae Giles sensu lato and 115 An. funestus Giles wild female mosquitoes were compared using three methods to determine cutoff absorbance values for positivity of a Plasmodium falciparum Welch enzyme-linked immunosorbent assay (ELISA). Positive controls were based on P. falciparum circumsporozoite protein. As negative controls, four wild male Anopheles were included on each microtitre plate; tests were repeated on four consecutive days for each plate.
Infection rates were estimated at 13.1–22.8% using the mean absorbance value of negative controls plus three standard deviations, 11.7–12.8% using double the mean and 12.5–13.6% using the fixed cut-off value of 0.20 (allowing for 20% variation in negative control absorbance values).
Observed agreement for positivity or negativity among samples tested four times was 98.6% for the 2× mean method, 97.2% for the fixed cut-off 0.20 value, but only 82.7% for the mean +3 SD method. It was concluded that the 2× mean cut-off method is most reliable for field studies. P. falciparum sporozoite rates of 12.2% in An. funestus and 11.9% in An. gambiae s. l . were thus determined on the basis of the 2× mean cut-off method.
This comparative evaluation demonstrates that vector infectivity rates can be seriously over-estimated from sporozoite ELISA tests, by as much as 87% in one case considered here, depending on the absorbance cut-off method applied for negative controls. 相似文献
Infection rates were estimated at 13.1–22.8% using the mean absorbance value of negative controls plus three standard deviations, 11.7–12.8% using double the mean and 12.5–13.6% using the fixed cut-off value of 0.20 (allowing for 20% variation in negative control absorbance values).
Observed agreement for positivity or negativity among samples tested four times was 98.6% for the 2× mean method, 97.2% for the fixed cut-off 0.20 value, but only 82.7% for the mean +3 SD method. It was concluded that the 2× mean cut-off method is most reliable for field studies. P. falciparum sporozoite rates of 12.2% in An. funestus and 11.9% in An. gambiae s. l . were thus determined on the basis of the 2× mean cut-off method.
This comparative evaluation demonstrates that vector infectivity rates can be seriously over-estimated from sporozoite ELISA tests, by as much as 87% in one case considered here, depending on the absorbance cut-off method applied for negative controls. 相似文献
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ANN H. SZYSZKO BESSEMARIE L. PRAZAK CHARLES F. EHRET WILLIAM J. EISLER JOHN J. WILLE 《The Journal of eukaryotic microbiology》1968,15(4):781-785
SYNOPSIS. A multi-unit automatic sampling device for investigation of microbial growth under a wide variety of conditions is described. The kinetics of asynchronous population growth for batch cultures of Tetrahymena pyriformis (W) at several temperatures show that there are 2 distinct growth phases: an exponential ultradian growth phase that is strongly temperature dependent and a non-stationary growth phase, the infradian phase, that shows little or no temperature dependence over the range from 15–27 C. 相似文献
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MICHAEL D. BAKER CHARLES R. VOSSBRINCK JAMES J. BECNEL JOSEPH V. MADDOX 《The Journal of eukaryotic microbiology》1997,44(3):220-225
ABSTRACT. Sequences of the small subunit rRNA genes of Amblyospora californica and an Amblyospora sp. from Culex salinarius were determined. These sequences were compared phylogenetically with 16 other microsporidia. The results suggest Amblyospora forms a sister taxon to the rest of the microsporidia examined. The basal position of Amblyospora is discussed with respect to the evolution of microsporidian life cycles. These sequences represent the longest microsporidian small subunit rRNA genes sequenced to date, 1,359 and 1,358 bp, respectively. Structural features and GC content (49% for both) are comparable to those of other microsporidia which have been sequenced. 相似文献
7.
Akaike's information criterion and the histogram 总被引:1,自引:0,他引:1
8.
SUMMARY. 1. The predation-balanced polymorphism of Ceriodaphnia cornuta (a small-eyed horned form and a large-eyed unhorned form) in Lake Gatun, Panama, is re-examined approximately 12 years after the original study (Zaret, 1972a). We consider morphological variability, distribution and fecundity of the population inhabiting Laboratory Bay.
2. The two morphological characters emphasized by Zaret, eye size and horn length, are studied in detail. The C. cornuta population exhibits wide, yet continuous variation; coefficients of variation are 28% or eye diameter and range from 114% to 136% for horn and spine lengths. Phenotypic variation in the population is characterized by: (1) negative correlations between spine lengths and eye size; (2) positive correlations among spines from different body regions (anterior horn, lateral spines, and tail spine); and (3) weak correlations between body length and spine lengths.
3. While the horned and unhorned forms continue to coexist in Laboratory Bay. the frequencies of horned forms have increased in the open water areas since the time of the original study. The increase in horned form frequencies may be due to changes in fish predation intensity. Did vertical distribution patterns of the forms remain very similar to each other.
4. In contrast to previous laboratory findings, egg ratio calculations from field samples revealed similar clutch sizes for the horned and unhorned forms. The egg development time of the horned form, however, was found to be approximately 30% longer than that of the unhorned form, perhaps because of increased moulting difficulties produced by the presence of spines. 相似文献
2. The two morphological characters emphasized by Zaret, eye size and horn length, are studied in detail. The C. cornuta population exhibits wide, yet continuous variation; coefficients of variation are 28% or eye diameter and range from 114% to 136% for horn and spine lengths. Phenotypic variation in the population is characterized by: (1) negative correlations between spine lengths and eye size; (2) positive correlations among spines from different body regions (anterior horn, lateral spines, and tail spine); and (3) weak correlations between body length and spine lengths.
3. While the horned and unhorned forms continue to coexist in Laboratory Bay. the frequencies of horned forms have increased in the open water areas since the time of the original study. The increase in horned form frequencies may be due to changes in fish predation intensity. Did vertical distribution patterns of the forms remain very similar to each other.
4. In contrast to previous laboratory findings, egg ratio calculations from field samples revealed similar clutch sizes for the horned and unhorned forms. The egg development time of the horned form, however, was found to be approximately 30% longer than that of the unhorned form, perhaps because of increased moulting difficulties produced by the presence of spines. 相似文献
9.
Potassium-Ammonium Uptake Interactions in Tobacco Seedlings 总被引:6,自引:0,他引:6
SCHERER HEINRICH W.; MACKOWN CHARLES T.; LEGGETT J. EVERETT 《Journal of experimental botany》1984,35(7):1060-1070
Short-term (< 12 h) uptake experiments were conducted with67-week-old tobacco (Nicotiana tabacum L. cv. Ky 14)seedlings to determine absorption interactions between K+ andNH4+. At equal solution concentrations (0.5 mol m3) netK+ uptake was inhibited 3035% by NH4+ and NH4+ uptakewas decreased 924%. Removal of NH4+ resulted in completerecovery in K+ uptake rate, but NH4+ uptake rate did not recoverwhen K+ was removed. In both cases, inhibition of the uptakerate of one cation saturated as the concentration of the othercation was increased up to 0.5 mol m3. The relative effectof K+-NH4+ interactions was not altered when Cl- was replacedwith SO42, but the magnitudes of the uptake rates wereless in the absence of Cl-. The Vmax for NH4+ uptake was reducedfrom 128 to 105 µmol g1 dry wt. h1 in thepresence of 0.5 mol m3 K+ and the Km for NH4+ doubledfrom 12 to 27 mmol m3 in the presence of K+. The resultsof these K+-NH4+ experiments are interpreted as mixed-noncompetitiveinteractions. However, an enhanced efflux of K+ coupled to NH4+influx via an antiporter cannot be ruled out as contributingto the decrease in net K+ uptake. Key words: Nicotiana tabacum, K+, NH4+, Uptake interactions 相似文献
10.
Interactions between Marek's Disease Herpesvirus and Avian Leucosis Virus in Tissue Culture 总被引:3,自引:0,他引:3
A GROUP B herpesvirus is important in the aetiology of Marek's disease, a highly contagious lymphoproliferative disease of chickens1,2. Chicks inoculated with enveloped Marek's disease herpesvirus (MDHV), extracted from feather follicle epithelium of chickens with the disease, developed tumour-like aggregates of lymphoid cells in the viscera and frequently in the peripheral nerves3,4. Cultures of chicken embryo fibroblast (CEF) cells infected with MDHV develop discrete foci of altered cells5. Our data show that MDHV infection of cultures of CEF cells, previously infected with an avian leucosis virus (RAV-2), results in both a reduction in the number of MDHV foci and an increase in the complement fixing avian leucosis antigen (COFAL)6 titre. 相似文献