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1.
The events that characterize egg formation and maturation inPteris cretica were investigated using transmission electronmicroscopy and electron microscope microprobe analysis. Theydid not differ significantly from those described for sexuallyreproducing ferns. The significance of these findings is discussedin relation to current theories concerning phase change in ferns. Pteris cretica, fern, apogamy, agamospory, transmission electron microscopy, oogenesis 相似文献
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Modifications of anionic-lipid domains preceding membrane fusion in guinea pig sperm 总被引:19,自引:15,他引:4 下载免费PDF全文
The relationship between anionic-lipid concentration and the functional properties of plasma-membrane domains was explored using the guinea-pig sperm membrane as a model, with polymyxin B (PXB) as a probe. Areas of plasmalemma specialized for fusion during the acrosome reaction had a higher affinity for the probe than adjacent nonfusigenic regions. In addition, capacitation--a process preceding acrosome:plasma-membrane fusion--markedly enlarged the area susceptible to PXB binding over the acrosomal cap. Protease treatment mimicked capacitation by increasing the acrosome-reaction incidence as well as PXB binding, at enzyme concentrations not affecting the surface coat nor altering filipin/sterol localization. Both proteolytic digestion and capacitation failed to augment PXB- or filipin-affinity in nonfusigenic zones, such as the post-acrosomal segment, including its particle-free maculae. Incubation of sperm in capacitating medium supplemented with 32P-labeled phosphate, followed by lipid extraction, thin-layer chromatography, and autoradiography, revealed a radioactive band comigrating with cardiolipin and phosphatidic acid. Vermiform protrusions elicited by PXB in the outer lamellae of cardiolipin- phosphatidylcholine liposomes resembled those seen in fusional regions of sperm membrane. We conclude that (a) differing concentrations of anionic lipids are found in adjacent domains of the sperm plasma membrane; (b) these domains mirror the functional regions of the membrane, with higher anionic-lipid concentrations localized over fusional zones; (c) the surface coat does not participate in the maintenance of such domains; (d) anionic-lipid synthesis may contribute to their formation; and (e) anionic-lipid concentrations increase as the membrane becomes fusionally competent, indicating that cellular modulation of lipid domains accompanies regulation of membrane function. 相似文献
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The chemotherapeutic potential of salicylhydroxamic acid (SHAM) was studied in adult rats infected with a strain of Trypanosoma brucei that kills the rats in about 100 hr. The median lethal dose, administered intraperitoneally in a carboxymethyl-cellulose suspension, is approximately 820 mg/kg body weight for male and 850 mg/kg for female rats. The apparent cause of death is severe depression of the central nervous system.Half-maximal inhibition of O2 uptake by trypanosomes in vitro requires 15 μM SHAM, whereas 100 μM inhibits over 90%. This inhibitory effect on trypanosome respiration was used as a biological assay for the effective SHAM concentration in rat plasma. After administration of a sublethal SHAM dose to rats, the effective plasma SHAM concentration rose rapidly to about 500 μM and then fell to about 10 μM at 4 hr. Nevertheless, this dose did not significantly affect the survival time of rats infected with T. brucei. Even if, by repeated SHAM administration, the plasma SHAM concentration was kept at around 100 μM for more than 4 hr, no therapeutic effect was observed.These results show that O2 uptake is not essential for the survival of trypanosomes in rats and they support the idea that bloodstream trypanosomes have an alternative pathway for glycolysis, allowing energy production in the absence of respiration.The possibility that SHAM or other inhibitors of trypanosome respiration could stilll be trypanocidal if used in conjunction with another inhibitor of glycolysis is discussed. 相似文献
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GUY WOODWARD JOHN B. DYBKJÆR JÓN S. ÓLAFSSON GÍSLI M. GÍSLASON ELÍSABET R. HANNESDÓTTIR NIKOLAI FRIBERG 《Global Change Biology》2010,16(7):1979-1991
The Earth is experiencing historically unprecedented rates of warming, with surface temperatures projected to increase by 3–5 °C globally, and up to 7.5 °C in high latitudes, within the next century. Knowledge of how this will affect biological systems is still largely restricted to the lower levels of organization (e.g. species range shifts), rather than at the community, food web or ecosystem level, where responses cannot be predicted from studying single species in isolation. Further, many correlational studies are confounded with time and/or space, whereas experiments have been mostly confined to laboratory microcosms that cannot capture the true complexity of natural ecosystems. We used a ‘natural experiment’ in an attempt to circumvent these shortcomings, by characterizing community structure and trophic interactions in 15 geothermal Icelandic streams ranging in temperature from 5 °C to 45 °C. Even modest temperature increases had dramatic effects across multiple levels of organization, from changes in the mean body size of the top predators, to unimodal responses of species populations, turnover in community composition, and lengthening of food chains. Our results reveal that the rates of warming predicted for the next century have serious implications for the structure and functioning of these fragile ‘sentinel’ ecosystems across multiple levels of organization. 相似文献
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Md. Ashraful Alam Milan Skalicky Muhammad Rezaul Kabir Md. Monwar Hossain Md. Abdul Hakim Md. Siddikun Nabi Mandal Rabiul Islam Md. Babul Anwar Akbar Hossain Fahmy Hassan Amaal Mohammadein Muhammad Aamir Iqbal Marian Brestic Mohammad Anwar Hossain Khalid Rehman Hakeem Ayman EL Sabagh 《Phyton》2021,90(4):1301-1320
Globally among biotic stresses, diseases like blight, rust and blast constitute prime constraints for reducing wheat
productivity especially in Bangladesh. For sustainable productivity, the development of disease-resistant lines and
high yielding varieties is vital and necessary. This study was conducted using 122 advanced breeding lines of
wheat including 21 varieties developed by Bangladesh Wheat and Maize Research Institute (BAMRI) with aims
to identify genotypes having high yield potential and resistance to leaf blight, leaf rust and blast diseases. These
genotypes were evaluated for resistance against leaf blight and leaf rust at Dinajpur and wheat blast at Jashore
under field condition. Out of 122 genotypes tested, 20 lines were selected as resistant to leaf blight based on
the area under the diseases progress curve (AUDPC) under both irrigated timely sown (ITS) and irrigated late
sown (ILS) conditions. Forty-two genotypes were found completely free from leaf rust infection, 59 genotypes
were identified as resistant, and 13 genotypes were identified as moderately resistant to leaf rust. Eighteen genotypes were immune against wheat blast, 42 genotypes were categorized as resistant, and 26 genotypes were identified as moderately resistant to wheat blast. Molecular data revealed that the 16 genotypes showed a positive 2NS
segment among the 18 immune genotypes selected against wheat blast under field conditions. The genotypes
BAW 1322, BAW 1295, and BAW 1203 can be used as earlier maturing genotypes and the genotypes BAW
1372, BAW 1373, BAW 1297 and BAW 1364 can be used for lodging tolerant due to short plant height. The genotypes WMRI Gom 1, BAW 1349 and BAW 1350 can be selected for bold grain and the genotypes WMRI Gom 1,
BAW 1297, BAW 1377 can be used as high yielder for optimum seeding condition but genotypes BAW 1377
and BAW 1366 can be used for late sown condition. The selected resistant genotypes against specific diseases can be used in the further breeding program to develop wheat varieties having higher disease resistance and
yield potential. 相似文献