Teaching English Humanely: An Experiment in Interaction in English Teacher Preparation

Student-centered teaching techniques were used with a group of English teachers to develop interaction. The objective was to make the teaching and learning of English more palatable, more fun, and more exciting

Tell Something About Yourself…

Teachers and society in general make too many assumptions based on students\u27 names, skin color, language habits, clothing, where they live, and religious preference

Induction of embryogenesis in [isolated] microspores and pollen of Brassica napus L. cv. Topas

Artificial systems to produce plant embryos are important tools for basic research as well as for plant breeding. It is possible to produce large amounts of embryos by methods like somatic embryogenesis or embryogenic microspore cultures. Such high amounts of embryos, which are easier to handle than zygotic embryos, are the prerequisite for biochemical and molecular genetic investigations on the one hand, and for biotechnological use on the other hand. Moreover, embryos derived from microspores or pollen represent a very efficient basis for the production of plant hybrids: Because of their haploid origin, microspore-derived embryos are after diploidization dihaploid, and thus, homozygous.The induction of embryogenesis in microspores and pollen of Brassica napus is realized by their cultivation under heat shock conditions (32 °C for at least 24 h). This dissertation presents results from our investigations on the induction phase of embryogenesis. Cellular changes during the first 24 h of cultivation of microspores and pollen were analysed to discern cytological differences between this induction phase of embryogenesis and the normal pattern of pollen development in planta. Combining light as well as electron-microscopy for the analysis of the cytoskeleton (microtubules and microfilaments), it was shown that the development of microspores and pollen in B. napus to a mature, tricellular microgametophyte is comparable to other angiosperms. Only the disappearance of the central vacuole before microspore mitosis is different from the common pathway (Chapter 2). Stage specific developmental patterns of microtubules and microfilaments could be detected in the microspores and pollen.Symmetrical divisions are a prerequisite for the embryogenic development of cultivated microspores and pollen, and three pathways for the induction of such divisions were identified (Chapter 3). (i) In vacuolated microspores cultivation under embryogenic conditions causes a migration of the nucleus to the centre of the cell where the division takes place. This phenomenon is accompanied by the disruption or altered formation of the microtubules. (ii) In late microspores the embryogenic conditions cause a turn of the mitotic spindle up to 90°. Both events (i and ii) result in symmetrically divided cells forming a bicellular proembryo. (iii) The developmental switch from young, bicellular pollen to the formation of proembryos is caused by a disrupted pollen development (arrest of the generative cell at the pollen wall) followed by division of the vegetative cell. In this case, microtubules, normally detectable in the vegetative cell perpendicular to the generative cell, are disrupted. In summary, all three pathways can lead to the formation of proembryos, and the microtubular cytoskeleton seems to be involved in these developmental changes. Although changes were also visible concerning the microfilaments under embryogenic conditions, their role in the induction of embryogenesis could not be confirmed.Because of the obvious changes in the cell cycle of microspores and pollen cultivated under embryogenic conditions, the synthesis of DNA was investigated in vivo and in vitro (Chapter 4). The incorporation and detection of bromodeoxyuridine as well as the determination of the ploidy level of the nuclei by microspectrophotometry were used for these investigations. DNA replication could be shown in vivo within the nucleus of the late microspore and also within the generative nucleus of the late bicellular pollen. In normal development the vegetative nucleus remains in the G1- phase. Under embryogenic conditions, the pattern of replication in microspores remained the same, but the vegetative nucleus of the young bicellular pollen re-entered the cell cycle and exhibited DNA synthesis.Changes in phosphorylation patterns were analysed using the monoclonal antibody MPM-2 (Chapter 5). The antibody MPM-2, raised against mitotic proteins of HeLa-cells, recognizes phosphorylated, mitosis-specific proteins in animal and plant cells. In developing microspores and pollen of B. napus, MPM-2 bound to proteins of all developmental stages, especially to proteins in the nuclei. Moreover, there were no differences in phosphorylated epitopes between microspores and pollen cultivated under embryogenic and non-embryogenic conditions. This might be caused by the fact that this antibody recognizes phosphorylated epitopes of various proteins.Because of the heat shock conditions used for the induction of embryogenesis, the subcellular localisation of heat shock proteins (HSPs) was performed (Chapter 6). Western blot analysis of proteins separated by two-dimensional gel electrophoresis revealed a strong signal at 70 kDa. Immunocytochemical investigations using an antibody raised against HSP70 showed a distinct stage- specific subcellular localization of HSP70 in vivo as well as in vitro. The embryogenic cultivation caused an altered localization of HSP70, which became detectable within the nucleus of the vegetative cell. Its localization could therefore be correlated with the initiation of DNA replication. Possible relations between HSP70 and replication were discussed.Chapter 7 describes the localisation of a specific mRNA within developing microspores and pollen of B. napus and Arabidopsis thaliana. Using freeze sectioned material and in situ- hybridization with a digoxygenin labelled probe, specific gene expression was demonstrated for the generative cell of both species.Finally, the expression of polarity during the development of microspore-derived and zygotic embryos was compared (Chapter 8). Investigations by scanning electron microscopic techniques showed that the embryo formation between them are similar from the globular stage onwards. The distribution of calcium ions, calmodulin and starch was used to find early signs of polarity. However, the accumulation of starch and the position of a residual pollen wall were the only hints for a predisposition of the radial axis of the developing embryo.In chapter 9 the embryogenesis in isolated microspores and pollen is considered as a biphasic process. The induction phase of embryogenesis represents the dedifferentiation of a developing organism followed by differentiation to a real plant embryo. Our results are combined with results of other groups to create a general scheme on induction of embryogenesis in microspores and pollen of B. napus.</em

Collisional and Radiative Effects in Transient sub-Doppler Hole Burning: Double Resonance Measurements in CN

We report transient hole-burning and saturation recovery measurements in the CN radical with MHz frequency resolution and 20 ns time resolution. Narrow velocity groups of individual hyperfine levels of selected rotational states in CN (X{sup 2} {Sigma}{sup +}) are depleted and excited (A{sup 2}{pi}{sub i}) with a saturation laser and probed by a counterpropagating, frequency modulated probe beam. Recent work in our lab has used this method to measure and characterize the hyperfine splittings for a set of rotational, fine structure, and parity components of CN (A{sup 2}{pi}{sub i}, v=1). Extending this work, we report time and frequency dependence of the saturation signals following abrupt switching of the CW saturation beam on and off with an electro-optic amplitude modulator. Recovery of the unsaturated absorption following the turnoff of the saturation beam follows pressure-dependent kinetics, driven by collisions with the undissociated NCCN precursor with a rate coefficient of 2 x 10{sup -9} cm{sup 3} s{sup -1} molec{sup -1}. Similar recovery kinetics are observed for two-level saturation resonances, where the signal observed is a combination of X- and A-state kinetics, as well as for three-level crossover resonances, which can be chosen to probe selectively the holefilling in the X state or the decay of velocity-selected A state radicals. The observed recovery rates are 8-10 times faster than the estimated rotationally inelastic contribution. The observed recovery rates are likely dominated by velocity-changing collisions in both X and A states, occurring with similar rates, despite the large difference in the properties of these electronic states. Transient signal risetimes following the turning on of the saturation pulse are consistent with the expected Rabi frequency. At lower pressures ({approx}50 mTorr) and higher beam power ({approx}200 mW), we can observe multiple Rabi cycles before collisions disrupt the coherent excitation and the transient signal reaches a steady state

Statistical Communication Theory

Contains reports on four research projects

Supramolecular organization of the human N-BAR domain in shaping the sarcolemma membrane

This is the final version of the article. Available from Elsevier via the DOI in this record.The 30 kDa N-BAR domain of the human Bin1 protein is essential for the generation of skeletal muscle T-tubules. By electron cryo-microscopy and electron cryo-tomography with a direct electron detector, we found that Bin1-N-BAR domains assemble into scaffolds of low long-range order that form flexible membrane tubules. The diameter of the tubules closely matches the curved shape of the N-BAR domain, which depends on the composition of the target membrane. These insights are fundamental to our understanding of T-tubule formation and function in human skeletal muscle.This work was supported by grants from the Deutsche Forschungsgemeinschaft (GRK 1026, SFB610) (A.A., T.G., J.B.), the BMBF ZIK program (A.M., J.B.), the European Regional Development Fund of the European Commission (A.M., T.G.: EFRE 1241 12 0001), and the state Sachsen-Anhalt (A.M., T.G., J.B.)

Statistical Communication Theory

Contains reports on eight research projects