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121.
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123.
Kim Moonza Kim Jinae Yoon Michung Choi Do-Il Lee Kwang-Min 《Plant Cell, Tissue and Organ Culture》2004,77(1):63-72
Anthers of Capsicum annuum L. were cultured on Murashige and Skoog (MS) medium containing 0.1 mg l−1 NAA and 0.1 mg l−1 kinetin. Inoculated anthers were subjected to 31 °C and development of microspores in anthers of varying stages was observed
cytologically using 4′-6-diamidino-2-phenylindol-2HCl (DAPI). Pepper was characterized by a strong asynchrony of pollen development
within a single anther. Percentage of pollen at different stages changed with the culture period, and the proportion of dead
pollen increased drastically from day 2 after culture. Microspores that were cultured at the late-uninucleate stage followed
one of two developmental pathways. In the more common route, the first sporophytic division was asymmetric and produced what
appeared to be a typical bicellular pollen. Embryogenic pollen was formed by repeated divisions of the vegetative nucleus.
In the second pathway, which occurred in fewer microspores, the first division was symmetric and both nuclei divided repeatedly
to form embryogenic pollen. In early-bicellular pollen, sporophytic pollen was produced through division of the vegetative
nucleus. In mid-bicellular pollen, the generative nucleus may undergo division to produce two or more sperm-like nuclei. However,
division of the generative nucleus alone to form the embryo was never observed. The anther stage optimal for embryo production
contained a large proportion (>75%) of early-binucleate pollen. Associations were found among the percentage of early-binucleate
pollen, the frequency of embryogenic multinucleate pollen, and the yield of pollen embryos. 相似文献
124.
Bruskova R. K. Zartdinova R. F. Satskaya M. V. Izmailov S. F. 《Russian Journal of Plant Physiology》2004,51(5):631-635
The organ topography of sucrose synthase and soluble acid invertase in pea seedlings at heterotrophic stage (3–14 days) was studied. Sucrose synthase was most active in the roots, with the highest activity on the 6–8th days. In the leaves, its activity decreased from day 3 to day 14. In the stems, sucrose synthase activity was at an invariantly low level. The patterns of sucrose synthase activity in etiolated and green plants were similar. As distinct from sucrose synthase, invertase activity was the highest in the stem, especially in etiolated plants. The peak of its activity was observed on the 6-8th days. In the leaves, invertase activity was lower but its pattern was the same. In the roots, acid invertase activity decreased from the 3rd day and did not depend on illumination. The conclusion is that differences in sucrose synthase and acid invertase activities in roots, leaves, and stem are determined by differences in the import of hydrolytic products of stored compound from the cotyledons as well as by different demands of these organs for these products for the processes of organ expansion and for the maintenance of organ metabolism. 相似文献
125.
以扁绒泡菌显型原质团为材料,进行细胞核的提纯、核骨架的制备及电镜观察。结果表明:用2mol/L NaCl+TritonX-100/NP40可得到具有复合纤维的核骨架,而用Lis + TritonX-100/NP40得到的核骨架具有核纤层,不使用RNase得到了具有网状的细胞核骨架,RNA在核骨架的结构形态中起重要作用。阐述了原质团中游离细胞核在细胞生物学研究中的意义。 相似文献
126.
127.
J Gerhart B Bast C Neely S Iem P Amegbe R Niewenhuis S Miklasz P F Cheng M George-Weinstein 《The Journal of cell biology》2001,155(3):381-392
The epiblast of the chick embryo gives rise to the ectoderm, mesoderm, and endoderm during gastrulation. Previous studies revealed that MyoD-positive cells were present throughout the epiblast, suggesting that skeletal muscle precursors would become incorporated into all three germ layers. The focus of the present study was to examine a variety of organs from the chicken fetus for the presence of myogenic cells. RT-PCR and in situ hybridizations demonstrated that MyoD-positive cells were present in the brain, lung, intestine, kidney, spleen, heart, and liver. When these organs were dissociated and placed in culture, a subpopulation of cells differentiated into skeletal muscle. The G8 antibody was used to label those cells that expressed MyoD in vivo and to follow their fate in vitro. Most, if not all, of the muscle that formed in culture arose from cells that expressed MyoD and G8 in vivo. Practically all of the G8-positive cells from the intestine differentiated after purification by FACS. This population of ectopically located cells appears to be distinct from multipotential stem cells and myofibroblasts. They closely resemble quiescent, stably programmed skeletal myoblasts with the capacity to differentiate when placed in a permissive environment. 相似文献
128.
On the evolution of clonal plant life histories 总被引:2,自引:0,他引:2
Clonal plant life histories are special in at least four respects: (1) Clonal plants can also reproduce vegetatively, (2) vegetative reproduction can be realised with short or long spacers, (3) and it may allow to plastically place vegetative offspring in benign patches. (4) Moreover, ramets of clonal plants may remain physically and physiologically integrated. Because of the apparent utility of such traits and because ecological patterns of distribution of clonal and non-clonal plants differ, adaptation is a tempting explanation of observed clonal life-history variation. However, adaptive evolution requires (1) heritable genetic variation and (2) a trait effect on fitness, and (3) it may be constrained if other evolutionary forces are overriding selection or by constraints, costs and trade-offs. (1) The few studies undertaken so far reported broad-sense heritability for clonal traits. Variation in selectively neutral genetic markers appears as pronounced in populations of clonal as non-clonal plants. However, neutral markers may not reflect heritable variation of life-history traits. Moreover, clonal plants may have been sampled at larger spatial scales. Empirical information on the contribution of somatic mutations to heritable variation is lacking. (2) Clonal life-history traits were found to affect fitness. However, much of this evidence stems from artificial rather than natural environments. (3) The relative importance of gene flow, inbreeding, and genetic drift, compared with selection, in the evolution of clonal life histories is hardly explored. Benefits of clonal life-history traits were frequently studied and found. However, there is also evidence for constraints, trade-offs, and costs. In conclusion, though it is very likely, that clonal life-history traits are adaptive, it is neither clear to which degree this is the case, nor which clonal life-history traits constitute adaptations to which environmental factors. Moreover, evolutionary interactions among clonal life-history traits and between clonal and non-clonal ones, such as the mating system, are not well explored. There remains much interesting work to be done in this field – which will be particularly interesting if it is done in the field. 相似文献
129.
Jacob Jelsing 《Hydrobiologia》2003,496(1-3):241-251
The distribution and structural components of dorsal ciliated organs (dco) in 15 species of the Spionidae were studied by scanning- and transmission electron microscopy. Based on the distribution patterns of dco, the investigated species are divided into four non-systematic groups: (I) paired anterior dco, (II) paired dco extending posteriorly for several chaetigers, (III) paired anterior dco in combination with unpaired, sexually dimorphic, metameric dco, and (IV) paired anterior dco in combination with paired, metameric dco. Previous ultrastructural studies have only included species possessing organs of groups I and III. In the present investigation the ultrastructure of dco found in Laonice bahusiensis and Spio cf. filicornis (species with dco of groups II and IV) is studied in an attempt to consider their homology. Apart from the metameric dco of group III, similarities of the cellular components of the dco indicate a homology to nuchal organs. 相似文献
130.
Optimal allocation to vegetative and sexual reproduction in plants: the effect of ramet density 总被引:3,自引:0,他引:3
Paweł Olejniczak 《Evolutionary ecology》2003,17(3):265-275
Vegetative reproduction is a very common alternative by which plants can contribute to the next generations. There are many considerations predicting which mode of reproduction, vegetative or sexual, should be favored and numerous experimental studies to verify them. However, the results are inconsistent especially when the effect of plant density is considered. I apply here a dynamic optimization model to predict the rate of vegetative and sexual reproduction in plants as a response to changes in the local plant density. The population is assumed to occupy a heterogeneous environment consisting of patches in which growth and reproduction of plants are possible and unfavorable space between them. As the environment is globally stable, the seeds, which can disperse without restriction, exhibit a constant recruitment rate. The ramets are assumed to settle only within the patch of the mother plant. The rate of ramet production effects local density, which in turn determines ramet recruitment. The optimal strategy maximizes the expected lifetime genetic contribution, realized via both vegetative and sexual reproduction. The solutions obtained under these assumptions are dualistic. The model predicts that different approaches applied in studying the effect of ramet density should give opposite outcomes. When the comparison is between patches in natural populations, a positive relationship between relative ramet allocation and density is expected. When the density is experimentally manipulated or its effect is analyzed across different successional stages, a negative relationship should be found. The results seem to be confirmed by empirical studies. 相似文献