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61.
ABSTRACT. The temporal changes in the size and pH of digestive vacuoles (DV) in Paramecium caudatum were reevaluated. Cells were pulsed briefly with polystyrene latex spheres or heat-killed yeast stained with three sulfonphthalein indicator dyes. Within 5 min of formation the intravacuolar pH declined from ~7 to 3. With the exception of a transient and early increase in vacuolar size, vacuole condensation occurred rapidly and paralleled the acidification so that vacuoles reached their lowest pH and minimal size simultaneously. Neutralization and expansion of vacuole size began when vacuoles were GT8 min old. No labeled vacuoles were defecated prior to 21 min after formation but almost all DV were defecated within 1 h so that the digestive cycle of individual vacuoles ranged from 21 to 60 min. Based on these size and pH changes, the presence of acid phosphatase activity, and membrane morphology, digestive vacuoles can be grouped into four stages of digestion. The DV-I are GT6 min old and undergo rapid condensation and acidification. The DV-II are between 4 to 10 min old and are the most condensed and acidic vacuoles. The DV-III range in age from 8 to ~20 min and include the expanding or expanded vacuoles that result from lysosomes fusing with DV-II. The DV-IV are GD21 min old, and since digestion is presumably completed, they can be defecated. The rise in intravacuolar pH that accompanies vacuole expansion suggests that lysosomes play a role in vacuole neutralization in addition to their degradative functions. The acidification and condensation processes in DV-I appear to be unrelated to lysosomal function, as no acid phosphaiase activity has been detected at this stage, but may be related to phagosomal functions important in killing food organisms, denaturing proteins prior to digestion, and preparing vacuole membrane for fusion with lysosomes. 相似文献
62.
The Onset of Germination Ability in Developing Wheat 总被引:1,自引:0,他引:1
GOSLING PETER G.; BUTLER RICHARD A.; BLACK MICHAEL; CHAPMAN JOHN M. 《Journal of experimental botany》1981,32(3):621-627
The ability of primary wheat grains (cv. Sappo) to germinatewas determined at different times from anthesis. Fresh, prematurelyharvested grains germinated best at low temperatures (<10°C). The temperature range over which appreciable germinationtook place broadened and the maximum percentage germinationachieved increased with lengthening time between anthesis andharvest. Chilling and exogenous applications of GA3 each affectedthe rate of germination and the maximum percentage germinationof grains in their own ways. The results are discussed in relationto the identification of dormancy in wheat grains. 相似文献
63.
64.
Larval Feeding in Echinoderms 总被引:2,自引:1,他引:1
In all four types of feeding echinoderm larvae, particles areretained upstream from the ciliated band, probably by an inducedlocal reversal of ciliary beat. Comparative studies and theoreticalconsiderations suggest that increasing the length of the bandmay be the only means of increasing the rate at which wateris processed for paniculate food. This would account for thelong looping band and late development of adult structures inechinoderm larvae. Estimates of the minimum food requirementsof early echinplutei and of uptake of amino acids by embryosare calculated. Various means of rejecting particles are describedand observations related to nervous control of feeding and rejectionare discussed. The possible disadvantages of larvae developingfrom smaller but more numerous eggs are discussed. It is arguedthat loss of a feeding larval stage is usually an irreversibleevolutionary change in echinoderms, and some general implicationsof the irreversibility of such a change in life history arementioned. 相似文献
65.
RICHARD A. THULBORN 《Lethaia: An International Journal of Palaeontology and Stratigraphy》1978,11(3):185-198
Thulborn, Richard A. 1978 07 15: Aestivation among ornithopod dinosaurs of the African Trias. Lethaia . Vol. 11, pp. 185–198. Oslo. ISSN 0024–1164.
Dental and circumstantial evidence supports the theory that ornithopod dinosaurs of the African Red Beds responded to seasonal changes in their environment by resorting to aestivation (dry season dormancy). One group of ornithopods. the heterodontosaurids. apparently suppressed tooth replacement to permit efficient grinding of their plant food and probably replaced their entire cheek dentitions while aestivating. The sympatric fabrosaurid ornithopods had a simple open-and-shut jaw action and replaced their teeth continuously in standard reptilian fashion. Seasonal dormancy must have imposed major constraints on the lives of fabrosaurids and heterodontosaurids. and these constraints are summarized in the model of a circannual life cycle. 相似文献
Dental and circumstantial evidence supports the theory that ornithopod dinosaurs of the African Red Beds responded to seasonal changes in their environment by resorting to aestivation (dry season dormancy). One group of ornithopods. the heterodontosaurids. apparently suppressed tooth replacement to permit efficient grinding of their plant food and probably replaced their entire cheek dentitions while aestivating. The sympatric fabrosaurid ornithopods had a simple open-and-shut jaw action and replaced their teeth continuously in standard reptilian fashion. Seasonal dormancy must have imposed major constraints on the lives of fabrosaurids and heterodontosaurids. and these constraints are summarized in the model of a circannual life cycle. 相似文献
66.
RICHARD BECKWITT 《Zoological Journal of the Linnean Society》1981,71(2):237-247
The genetic control of morphological variation (expressed as heritability) was examined by means of laboratory culture in Pileolaria pseudomilitaris. Fourteen of 22 traits examined were shown to have an appreciable genetic component, after an analysis of variance among groups of full siblings. The range of variability for several traits is as large within a single sibling group as the difference between described species in the family.
Comparisons among samples of P. pseudomilitaris from two habitats revealed no consistent morphological dillerences. A similar comparison between P. pseudomilitaris and its nearest congener, I', potswaldi , indicated significant differences for 15 of 22 traits, although ranges overlapped for all bin two of these. 相似文献
Comparisons among samples of P. pseudomilitaris from two habitats revealed no consistent morphological dillerences. A similar comparison between P. pseudomilitaris and its nearest congener, I', potswaldi , indicated significant differences for 15 of 22 traits, although ranges overlapped for all bin two of these. 相似文献
67.
RICHARD HYLBOM 《Zoologica scripta》1991,20(1):1-6
Arenonemertes arenicolus sp.n. is described from the Gullmar Fjord, Sweden. It differs from A. microps Friedrich, 1933 in: (1) lacking cephalic glands, (2) having an undivided caecum on the midgut, whereas the caecum is divided into three lobes in A. microps , and (3) the position of the nephridial ducts in relation to the lateral nerves (dorsal instead of ventral). Arenonemertes microps is still considered a valid species, but it is poorly described and the type material has been lost. 相似文献
68.
69.
Experimentally increased soil temperature causes release of nitrogen at a boreal forest catchment in southern Norway 总被引:5,自引:0,他引:5
Boreal forest ecosystems are sensitive to global warming, caused by increasing emissions of CO2 and other greenhouse gases. Assessment of the biological response to future climate change is based mainly on large-scale models. Whole-ecosystem experiments provide one of the few available tools by which ecosystem response can be measured and with which global models can be evaluated. Boreal ecosystem response to global change may be manifest by alterations in nitrogen (N) dynamics, as N is often the growth limiting nutrient. The CLIMEX (Climate Change Experiment) project entails catchment-scale manipulations of CO2 (to 560 ppmv) and temperature (by + 3 to + 5 °C) to whole forest ecosystems in southern Norway. Soil temperature is increased at 400-m2 EGIL catchment by means of electric cables placed on the soil surface. Soil warming at EGIL catchment caused an increase in nitrate and ammonium concentrations in runoff in the first year of treatment. We hypothesize that higher temperature increased N release by mineralization. Whether these responses are only transient will be shown by additional years' treatment. 相似文献
70.
RICHARD D. WARD 《Systematic Entomology》1976,1(3):227-240
Immature stages of Lutzomyia anduzei (Rozeboom), L.antunesi (Coutinho), L. flaviscutellata (Mangabeira), Psychodopygus davisi (Root), Ps.paraensis (Costa Lima) and Ps.lainsoni Fraiha & Ward are described from specimens reared in the laboratory. The Lutzomyia species are members of the intermedia group, though L. flaviscutellata larvae more closely resemble those of Psychodopygus species. The larvae of L.anduzei and L. antunesi are separable on minor setal differences and are similar to previously described members of the intermedia group. Ps. paraensis is distinguishable from the other two Psychodopygus species described, by the absence of prothoracic seta 2. Head seta 5 of Ps.davisi is about twice the length of that in Ps. paraensis and larvae of Ps.lainsoni are pale and characterized by colourless body setae 4 and 10. A key to the fourth instar larvae is given which includes all the known larvae of the intermedia group and of the genus Psychodopygus. Morphological differences in the Psychodopygus larvae do not appear to reflect the separation of the adults into series. 相似文献