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81.
ABSTRACT The storage carbohydrate granules from Euglena and Pavlova were compared by light and electron microscopy. Freezeetch studies demonstrated that while both types of granules are crystalline, they have different structures. The elemental microfibril of the euglenoid granule measures 4 nm, and the elemental striation of the granule from Pavlova is 22 nm. The granules each have a unique X-ray diffraction pattern. The storage carbohydrate granules from Pavlova are not the same as paramyton, and the term “paramylon” should be reserved for the euglenoid storage carbohydrate. 相似文献
82.
DAVID P. FOX BRUCE F. HILL DONALD M. SPOON GEORGE B. CHAPMAN 《The Journal of eukaryotic microbiology》1988,35(1):4-12
ABSTRACT. A sessile, tentacle-bearing protozoon, Heliophrya sp. (Suctoria, Ciliata), reproduces asexually by evaginative budding to form a ciliated swarmer, which begins metamorphosis to the adult form within 30 min of its release from the parent cell. Morphological features of embryogenesis were investigated using transmission and scanning electron microscopy and found to correspond, with certain exceptions, to the few previous reports concerning evaginative budding in suctorians. Following invagination of a portion of the pellicle to form an embryonic cavity within the parent cell, numerous kinetosomes, apparently formed de novo, organize into rows which surround the embryonic cavity and eventually develop cilia that project into the cavity. When the cavity is complete, its walls are extruded through an opening in the parent cell surface. Parent cell cytoplasm streams into the incipient swarmer, thus supplying it with at least the minimum requirement of all cytoplasmic organelles. The ciliated swarmer remains attached to its parent cell for several minutes before it detaches. A complete pellicle is formed in both parent and swarmer prior to detachment. The numerous mitochondria underlying the parent cell pellicle in the vicinity of the attachment area suggest that cross wall formation is an energy-dependent process. 相似文献
83.
CHRISTINE A. SUNDERMANN DAVID S. LINDSAY ROBERT E. TIBBS MARK A. BAILEY 《The Journal of eukaryotic microbiology》1988,35(4):465-469
The development of Caryospora bigenetica in vitro is described by light microscopy. Sporozoites from snake-derived oocysts were purified and inoculated onto cultures of primary testicle cells of the cotton rat, cotton rat kidney cells, and human fetal lung cells. Intracellular sporozoites were observed one and two days postinoculation (DPI). Motile, extracellular first-generation merozoites were present 3 DPI, and second-generation merozoites were present 5 DPI. Mature gamonts were observed 9 DPI and developed into unsporulated oocysts by 10 DPI. Oocysts sporulated in vitro, and excystation was observed. Cells that were penetrated by in vitro-produced sporozoites formed caryocysts by 16 DPI. To test infectivity of in vitro-derived stages, merozoites were removed from cultured cells 5 DPI and inoculated intraperitoneally into a mouse; infection resulted. Sporulated oocysts removed from cell cultures 12 DPI produced facial swelling in an orally inoculated cotton rat. 相似文献
84.
ABSTRACT. The purpose of this research was to determine whether mice could be protected from lethal challenge with Naegleria fowleri by prior intranasal exposure to pathogenic and nonpathogenic Naegleria. Mortality ranged from 0 to 100% for mice inoculated intranasally (i.n.) with 5 × 103 amebae of 13 human isolates of N. fowleri. Mice were immunized and challenged i.n. using live amebae of strains of low, medium, and high virulence. The greatest protection against lethal challenge was afforded by three immunizing doses of 103 amebae per dose of the strain of medium virulence. Nonpathogenic N. gruberi also was used to immunize mice i.n. against lethal challenge with N. fowleri. Protection was greater following immunization with N. gruberi than it was after immunization with N. fowleri, suggesting that nonpathogenic N. gruberi may be a better immunogen in protecting mice against lethal naeglerial challenge. 相似文献
85.
Estimates of Daily Energy Expenditure in Birds: The Time-Energy Budget as an Integrator of Laboratory and Field Studies 总被引:1,自引:1,他引:0
SYNOPSIS. Measures of energy expenditure by free-living birdscan provide quantitative testsof a number of ecological theories,regarding such diverse phenomena as foraging strategies, resourcecompetition, or parental investment. Our confidence in thesetests rests heavily on the confidence we have in the estimatedrates of energy expenditure. The most common approach to obtainingsuch estimates is the construction of time-energy budgets, inwhich the durations of ananimal's daily activities are multipliedby the respective energy costs of the activities, and thesecosts are summed. Our knowledge of the energy costs of activities,particularly locomotion, has greatly advanced in recent years,as has the ability to adequately assess thermoregulatory costs.Comparisons between timeenergy budgets and direct measures ofenergy expenditure obtained using doubly labeled water indicatethat time-energy budgets can yield accurate estimates of energyexpenditure. However, this is likely to be achieved only underfairly rigorous conditions in which resting costs, activitycosts, and thermoregulatory costs are all well described.Evidenceis accumulating to suggest that, under some conditions, energyexpenditure by birds reaches a maximum sustainable level, atwhich point it is limited by the physiological capacitiestoingest and assimilate energy. Under these conditions, behavioralresponses to changing physical environments and resource availabilitymay be critical to the maintenance of energy balance. 相似文献
86.
A rapid method for the detection of corynetoxins, tunicamycin-like antibiotics, is described. Test samples were applied to or grown on an agar medium and overlain with Clavibacter tritici which is highly sensitive to the toxins. The method could detect 50 ng of tunicamycin. Corynetoxins in a range of field and laboratory samples were readily detected. 相似文献
87.
Proplastids of both tapetal cells and microsporocytes were presentearly in anther development. Tapetal proplastids differentiatedprobablyinto elaioplastsat late microspore stage. The tapetalcytoplasm was completely resorbed by early tricellular pollenstage. Microspore proplastids differentiated into amyloplastsat early bicellular stage, and were present in both vegetativeand generative cells. In the generative cell, the amyloplastswere ephemeral and apparently degenerated within autophagicvacuoles. Plastids were absent from sperm cells. Vegetativecell amyloplasts increased in number apparently by fission suchthat one amyloplast produced one amyloplast and one proplastidper division. Mature pollen grains were estimated to containbetween 550 and 820 amyloplasts with only one starch granuleper plastid. Elaioplasts, amyloplasts, plastid division, plastid differentiation, starch granules, autophagy, Lolium perenne, Poaceae, rye-grass 相似文献
88.
DICKY S. YU ERIC G. KOKKO JOHN R. BARRON G. BRUCE SCHAALJE BRENT E. GOWEN 《Systematic Entomology》1992,17(4):389-395
Abstract. Image analysis was used to measure the morphological characters of wings of five species of Canadian Itoplectis (Ichneumonidae). The procedure to digitize and measure various elements of the wings with an image analyser is outlined. Specimens were assigned to species by discriminant analysis and independent univariate comparisons of 144 characters from cells, veins and vertices. All the fifty specimens used were assigned to the correct species by both methods. Image analysis of ichneumonid wings is an effective alternative to the conventional identification system. 相似文献
89.
The Influence of Carbon Dioxide and Daily Photon-flux Density on Optimal Leaf Nitrogen Concentration and Root: Shoot Ratio 总被引:5,自引:1,他引:4
Using a cost-benefit model, the leaf nitrogen concentrationand root : shoot ratio that maximize whole-plant relative growthrate are determined as a function of the above-ground environment(integrated daily photon flux density and the concentrationof carbon dioxide at the site of fixation within the leaf).The major advantage of this approach is that it determines theadaptive significance of leaf physiology by considering thefunctional integration of leaves and roots. The predicted responseto increasing daily photon flux densities is an increase inoptimal leaf N concentration (Nopt) and a concomitant increasein root: shoot ratio. Increased carbon dioxide concentrations,on the other hand, reduce Nopt and only slightly change root:shoot ratio. The observed increase in leaf nitrogen concentrationfound in plants growing at high altitudes (low CO2 partial pressure)is also predicted. Since these responses to light and CO2 maximizethe whole-plant relative growth rate, the observed adjustmentsthat plants make to light and carbon dioxide concentration appearto be adaptive. We show that the relationship between photosynthesis and leafnitrogen concentration is complex and depends on the light andCO2 levels at which photosynthesis is measured. The shape ofthis function is important in determining Nopt and the oppositeresponse of leaf nitrogen to light and carbon dioxide is shownto be the result of the different effects of light and CO2 onthe photosynthesis-leaf nitrogen curve. Plant growth, photosynthesis, leaf nitrogen, biomass allocation, optimization, carbon dioxide light 相似文献
90.
Two chilling-sensitive (Phaseolus vulgaris L., Zea mays L.)and two chilling-tolerant (Pisum sativum L., Spinacia oleraceaL.) species were raised in growth chambers under warm (28/18°Cday/night cycle) and cool (18/12°C) temperature regimes.Growth analysis techniques were used to evaluate leaf area andbiomass partitioning during early autotrophic growth. Plantsacclimated to both temperatures were measured for leaf gas exchangeand water potential ( 相似文献