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21.
DENNIS R. DIENER BROWER R. BURCHILL PAUL R. BURTON 《The Journal of eukaryotic microbiology》1983,30(1):83-90
ABSTRACT. The ultrastructure of the cortex beneath the fission furrow of dividing Stentor coeruleus was examined using scanning and transmission electron microscopy. During division, basal bodies, axonemes, and km fibers beneath the furrow were absorbed near the moving primordial oral apparatus, and a circumferential band of microtubules and filaments was formed at the base of the furrow. The location and orientation of this fibrous band suggest that it may be an important component of the cytokinetic machinery. Treatment with vinblastine sulfate (4 × 10-5 M) disrupted the circumferential microtubules and blocked division, which is consistent with this hypothesis. 相似文献
22.
Abstract. The patterns of growth in organs curving under the influence of gravity were analysed by time-lapse photography of cress and cucumber hypocotyls which were delimited into 1 mm zones by ion-exchange beads. Geotropic curvature resulted from changes in growth rate on both sides of the organ. Growth inhibition of varying degrees of intensity occurred in all the previously growing zones of the upper (concave) side. An absolute reduction in length due to compression frequently occurred in some zones. Also, in both species growth stimulation was observed on the lower (convex) side. The disparity in growth rate between the upper and lower surfaces varied with time, being more apparent in the subapical region in the first hour of curvature. A later promotion of growth rate on the lower surface subsequently increased the curvature of the more basal zones. Autotropic straightening occurred as a consequence of growth changes, both inhibitory and stimulatory, in the apical zones. These events indicate a polarity of response in which apical zones have precedence over basal zones. 相似文献
23.
Moult of some palaearctic migrant passerines was studied at a wintering site in northern Ghana, West Africa. We present data on moult pattern and estimated moult duration for a sample of species. Savi's Warbler Locustella luscinioides , Woodchat Shrike Lanius senator and probably Grasshopper Warbler Locustella naevia deviated from the ordinary descendent moult sequence. Different measures of moult speed (moult speed of retrapped individuals, growth of individual feathers, wing raggedness and first date of completion of moult) showed unexpectedly rapid moult among individuals of several species, notably the Great Reed Warbler Acrocephalus arundinaceus and the Sedge Warbler A. schoenobaenus. The rapid moult might be an adaptation to a limited period of abundant food which comes to an end at the beginning of the dry season. 相似文献
24.
Aphid consumption by larval and adult Tachyporus hypnorum (Coleoptera: Staphylinidae) in different reproductive states was compared under laboratory conditions. Post-overwintering (spring/summer) adults had a higher consumption rate of first/second instar Sitobion avenae (Hemiptera: Aphididae) than did overwintering adults. Choice experiments incorporating Isotoma viridis (Collembola: Isotomidae) and Sciara thomae (Diptera: Mycetophilidae) as alternative prey items showed that T. hypnorum had a strong preference for aphids at a range of prey frequencies. Numbers of aphids consumed were reduced when leaves infected with Erysiphe graminis f.sp. tritici (powdery mildew of wheat) were offered to beetles with aphids in choice experiments. Behavioural studies of adult T. hypnorum showed that foraging rates on wheat plants increased with increasing amounts of both mildew and aphids on plants. Feeding upon only the conidia of E. graminis was observed. Results are discussed in relation to previous data derived from gut dissection, to a field survey of alternative foods and to the phenology of T. hypnorum in relation to that of aphids in the wheat crop. 相似文献
25.
C. D. GREEN KATHERINE WILLIAMSON E. B. DENNIS T. McBURNEY † 《The Annals of applied biology》1981,97(3):303-309
Oxamyl treatment at drilling greatly increased the growth of the plants, the yield and quality of the peas harvested, in soil infested by small or large numbers of Heterodera goettingiana. Treated plants were continuing to set pods when non-treated plants were senescing. Rhizobium nodulation, sap nitrate and tissue nitrogen content were increased in treated plants. Oxamyl applied to growing plants reduced later nematode invasion and enabled root nodulation to proceed with an increase in tissue nitrogen but no increase in yield. Oxamyl applied at drilling in April was inactive against invasion by H. goettingiana in June, which enabled the nematode to multiply equally in treated and non-treated plots. The most economic treatments were at the smallest rates, giving the greatest increase in yield/kg of oxamyl applied. 相似文献
26.
Effects of Low Concentration of Ozone, Singly, and in Combination with Sulphur Dioxide on Net Photosynthesis Rates of Vicia faba L. 总被引:3,自引:0,他引:3
Net photosynthesis rates (PN) of Viciafaba plants were measuredin chambers containing either clean air or air containing between50 and 300 parts 109 ozone (O3) with or without 40 parts10 9 SO2. Exposure to O3 concentrations greater than 50 parts 109 for periods of 4 h resulted in reductions in PN with greaterreductions at higher concentrations. After exposure ceased,recovery of pre-exposure PN depended on O3 concentration. Exposureto less than 90. 100 parts 10 9 was followed by completerecovery after 20 h whereas 200-300 parts 10 9 resultedin visible injury and irreversible depression of PN. The additionof 40 parts 10 9 SO2 to O3 significantly decreased Psbut the effect of SO2 declined with increasing O3. The additionof SO2 had no significant affect on recovery patterns. It is postulated that Vicia faba plants are able to toleratethe absorption of O, up to a threshold above which progressivedecreases in PN occur due to effects on photosynthetic processes.The slow and sometimes incompletely reversible effects of O3on PN indicate cellular differences in the injury mechanismand repair capacity compared with the action of SO2 alone. Lowconcentrations of O3 with SO2 result in additive injury to PNsuggesting independent action of the pollutants, but the reductionin SO2 action with increasing O3 indicates a limit for potentialphysiological injury More the onset of visible injury. 相似文献
27.
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
28.
New durophagous arthrodires from Gogo, Western Australia 总被引:1,自引:0,他引:1
Three new monotypic genera of eubrachythorarid arthrodires with crushing toothplates are described from the Upper Devonian Gogo Formation of Western Australia as Bruntonichthys multidens gen. et sp. nov., Bullerichthysfascidens gen. et sp. nov. and Kendrickkhthys cavemosus gen. et sp. nov. Their structure and relationships are discussed within the framework provided by a sketch cladogram. All three are interchangeable with Coccosteus spp. but their phylogenetic relationships are not known in any detail. However, Kendrickkhthys does appear to be immediately related to Dinomylostoma from North America. 相似文献
29.
Analysis of growth during light-induced hook opening in cress 总被引:1,自引:1,他引:0
Abstract. Growth in various regions of the hypocotyls of dark-grown cress seedlings before and after exposure lo continuous white light has been analysed by time-lapse photography. In the dark, growth in the hook was minimal, the upward growth of the seedling being sustained by extension of the shank, especially the uppermost zones. Following irradiation, the hook and the remainder of the hypocotyl showed dissimilar growth responses. Previously growing regions of the shank were inhibited while zones within the hook, especially the apical end of the inner (concave) side, showed marked growth stimulation. These changes in growth rates commenced within 1 h from exposure to the light stimulus and thus considerably preceded any observable changes in hook angle. 相似文献
30.
THE RATIO OF CALCAREOUS AND ORGANIC SHELL COMPONENTS OF FRESHWATER SPHAERIID CLAMS IN RELATION TO WATER HARDNESS AND TROPHIC CONDITIONS 总被引:1,自引:0,他引:1
BURKY ALBERT J.; BENJAMIN MICHELE A.; CATALANO DENNIS M.; HORNBACH DANIEL J. 《Journal of Molluscan Studies》1979,45(3):312-321
Shells from 14 populations of sphaeriid clams including Sphaeriumstriatinum, S. simile, Pisidium walkeri, Musculim partumeiumand M. iransversum were analyzed for organic carbon (µgCmg1 shell), nitrogen (µg,N mg1 shell) andCaCOs (%CaCO3 of total clam dry weight). Habitat waters wereassessed for total hardness (expressed as ppm CaCo3), ppm Ca,ppm Mg, conductivity (µmho) and suspended organic Carbon(µgCl1). For all populations, shell organic C andN are positively correlated and there is an inverse relationshipbetween the amounts of shell CaCO3 and shell organic carbon.Trophic considerations give the best correlation with shelltype at the generic level of consideration since species ofMusculium are found at the opposite end of the trophic scale(eutrophic) from all other populations studied. For S. striatinum,the most extensively studied species, the amount of shell CaCO3is inversely related to water hardness. The selection of shellsin the Sphaeriidae is discussed in relation to structural-functionalneeds and habitat conditions
1 Present Address: Department of Biology, Syracuse University,Syracuse, New York 13210, U.S.A.
2 Present Address: Department of Zoology, Miami University,Oxford, Ohio 45056, U.S.A. (Received 5 December 1978; 相似文献