A novel approach to microspore embryogenesis in Brassica napus L.

The objective of this study was to investigate development of haploid embryos of 'Brassica napus' induced from isolated microspores, and to provide a comparison to the corresponding developmental stages of zygotic embryos. A novel method for induction and culture of microspore-derived (MD) embryos was designed, based on restricted sucrose supply and use of high molecular weight polyethylene glycol (PEG) as an osmoticum. Haploid embryos cultured under these conditions were studied, from the induction phase to the formation of cotyledonary embryos, through their maturation and desiccation. Finally, plantlet formation and their ex vitro acclimatization were assessed. Induction and formation of MD embryos was not affected by limited sucrose supply; embryos proceeded through globular, heart, torpedo and cotyledonary stages within two weeks. After exposure to light, PEG embryos turned dark green and appeared similar to dissected early cotyledonary stage zygotic embryos. Morphological changes during the time-course of microspore embryogenesis were studied using scanning electron microscopy. Early embryo development from embryogenic microspores to the globular stage was irregular and differed from that of zygotic embryos. However, at heart, torpedo and cotyledonary stages, PEG embryos were remarkably similar to their zygotic counterparts in size and shape, with well-developed cotyledons. Sucrose embryos were 2-3 times larger than PEG embryos, but cotyledons were small and poorly differentiated. Numerous large starch grains were observed in cells of sucrose embryos at the early cotyledonary stage, but were almost completely absent in PEG embryos. The characteristic presence of pollen wall remnants suggested an origin of polarity in MD embryos, possibly established in late uninuclear microspores and early bicellular pollen. Application of ABA and desiccation treatment improved the in vitro conversion frequency of both sucrose and PEG embryos. However, PEG plantlets directly transferred to soil had a higher survival rate and enhanced vigor during the acclimatization ex vitro. This novel microspore culture system is suitable for studies of in vitro embryogenesis with a broad range of plant species and should have important potential application in plant biotechnology and breeding programs

Sulfur retention by ash during coal combustion. Part I. A model of char particle combustion

A model for the combustion of porous char particles as a basis for modeling the process of sulfur retention by ash during coal combustion is developed in this paper. The model belongs to the microscopic intrinsic models and describes the dynamic behavior of a porous char particle during comustion, taking into account temporal and spatial changes of all important physical properties of the char particle and various combustion parameters. The parametric analysis of the enhanced model shows that the model represents a good basis for the development of a model for the process of sulfur retention by ash during coal combustion. The model enables the prediction of the values of all parameters necessary for the introduction of reactions between sulfur compounds and mineral components in ash, primarily calcium oxide

Sulfur self-retention in ash a grain model approach

A developed overall model for sulfur self-retention in ash during coal particle combustion is presented in the paper. The total sulfur content in char, after devolatilization, is evaluated using a derived correlation. It is assumed that sulfur retention during char combustion occurs due to the reaction between SO2 and the active part of the Ca in the form of uniformly distributed CaO grains. Parametric analysis shows that the process is limited by solid diffusion through the product layer formed on the CaO grains and that the most important coal characteristics which influence sulfur self-retention are coal rank, content of sulfur forms, molar Ca/S ratio and particle radius. The model predicts relatively well the levels of the experimentally obtained values of SSR efficiencies, as well as the influence of temperature, particle size and the surrounding conditions

Extended time of cold ischemia and its influence on the physiological function of human adult pancreatic islets

In this study we compared the effects of duration of cold ischemia (longer and shorter ischemia) on the yield, viability and preservation of the physiological function and insulin secretion of adult human pancreatic islets in short-term (seven days) culture. Based on the tested parameters, we established that there are no major differences between these two test groups and that the storage and transport of pancreatic tissue in physiological solution at 4 degrees C gives quite satisfactory results

Investigation of the suitability of Serbian lignites for burning in CFBC boilers

The results of the detailed investigations of behavior of lignites Kolubara and Kovin, in fluidized bed combustion are presented in the paper. Investigation was carried out due to the interest of the Serbian Electric Power Production Company to use CFBC boilers in the process of refurbishment of old pulverized coal combustion boilers. As a part of a feasibility study for CFBC use in power plants in Serbia, investigation of combustion characteristics of lignites was performed using original methodology introduced many years ago by Laboratory for Thermal Engineering and Energy. Methodology was approved by numerous investigations of more than 20 Yugoslav coals for FBC combustion, with the aim to determine design data for bubbling FBC boilers. The main attention in present investigation was paid to the problem of using methodology developed for bubbling FBC in the conditions present in CFBC boilers. Four samples of Kolubara lignite, with heat capacity from 2.5 to 8.5 MJ/kg, and different ash contents were investigated, and also lignite Kovin in the same range of heat capacity. Investigations were performed in three phases: (1) ultimate and proximate analysis, determination of ash sintering temperature by standard method and in fluidized bed laboratory oven, (2) investigations in laboratory fluidized bed furnace and determination of coal particle fragmentation, burning rate, start-up temperature and self-sulfure-capture and (3) investigation of combustion in pilot-plant in stationary combustion conditions. In conclusion, suitability of results obtained in BFBC conditions is approved, and earlier statement that lignites are suitable for BFBC is confirmed by the statement that lignites are even more suitable for burning in CFBC boilers. Considering differences between combustion and flow conditions in bubbling and circulating FBC boilers, behavior of the lignites in CFBC is discussed in details and optimal regime parameters of the CFBC boilers are determined. The results obtained will be used by Serbian Electric Power Production Company for evaluation of bid for CFBC boiler implementation in refurbishment of old thermal power plants.Proceedings of the 18th International Conference on Fluidized Bed Combustion, May 22-25, 2005, Toronto, Canad