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191.
Bart M. Nicolaï Jan F. Van Impe Peter A. Vanrolleghem Joos Vandewalle 《Antonie van Leeuwenhoek》1992,62(4):273-283
The mathematical model for the penicillin G fed-batch fermentation proposed by Heijnen et al. (1979) is compared with the model of Bajpai & Reuß (1980). Although the general structure of these models is similar, the difference in metabolic assumptions and specific growth and production kinetics results in a completely different behaviour towards product optimization. A detailed analysis of both models reveals some physical and biochemical shortcomings. It is shown that it is impossible to make a reliable estimation of the model parameters, only using experimental data of simple constant glucose feed rate fermentations with low initial substrate amount. However, it is demonstrated that some model parameters might be key factors in concluding whether or not altering the substrate feeding strategy has an important influence on the final amount of product.It is illustrated that feeding strategy optimization studies can be a tool in designing experiments for parameter estimation purposes. 相似文献
192.
Jan Schripsema Annemarie H. Meijer Frank van Iren Hens J. G. ten Hoopen Robert Verpoorte 《Plant Cell, Tissue and Organ Culture》1990,22(1):55-64
A simple non-invasive method for the characterization of growth of a plant cell suspension in a single culture flask is given. The dissimilation of sugars by a cell-culture causes a loss of weight of the contents of the culture flask, and can therefore be used to follow the growth in that single culture flask. Because a correction for water evaporation is necessary, accurate results can only be obtained when a stable closure is used (e.g. Silicosen T-type plugs). The dissimilation curves obtained in this way were correlated to the concentration of sugars in the medium, the dry weight and the fresh weight. From these correlations the amount of intracellularly stored carbohydrates could be estimated. Rate constants for CO2-diffusion were determined for different types of closure. These values allowed the estimation of CO2 levels inside the culture flasks from the dissimilation curves (CO2 release curves). The dissimilation curves obtained using this method can easily be related to other types of growth curves. Different growth-phases can be clearly distinguished, e.g. lag-phase, exponential growth-phase and stationary-phase. 相似文献
193.
Jan Aaseth Harald Frey Eystein Glattre Gunnar Norheim Jetmund Ringstad Yngvar Thomassen 《Biological trace element research》1990,24(2-3):147-152
Recently, we found that prediagnostic serum selenium concentration was significantly lower for cases developing thyroid cancer (n=43) than for controls. We assumed that redistribution of serum selenium into the affected tissue took place in the prediagnostic period. The present study was carried out to determine the physiological concentration of selenium in the thyroid, since very few data are available in the literature. The concentrations of selenium in the thyroid (n=45) and liver samples from Norwegians who had died because of acute illness or accidents were determined by hydride generation atomic absorption spectrometry. The mean selenium concentration was found to be 0.72±0.44 μg/g in the thyroid and 0.45±0.11 μg/g in the liver tissue. The surprisingly high concentration of selenium in apparently normal thyroids indicates that selenium has important functions in this organ. The remarkably broad range, together with the observation that no significant correlation exists between thyroid and liver concentrations, suggest that factors other than the selenium status are important determinants for the selenium concentration in the thyroid gland. This observation is consistent with our hypothesis that in carcinogenesis, prediagnostic processes influence the serum-/thyroid-ratio of selenium. 相似文献
194.
Harry Jan Swartz Robert Bors Fouad Mohamed S. Kristine Naess 《Plant Cell, Tissue and Organ Culture》1990,21(2):179-184
Shoot regeneration from Rubus leaves was obtained on a medium containing MS salts, vitamins and sugars, Staba vitamins, casein hydrolysate (100 mg l–1) and 10 M thidiazuron. Shoot regeneration from Malus leaves was obtained on N6 rice anther medium with 5 M thidiazuron. In vitro pretreatment of source shoots with either colchicine or thidiazuron enhanced the organogenic potential of detached leaves of two Rubus hybrids. The response to colchicine was quadratic and occurred at non-mutagenic concentrations (75–250 M). The response to thidiazuron was exponential between 0 and 5 M. When applied as a pretreatment, the effectiveness of several different cytokinins (benzyladenine, thidiazuron, zeatin) at enhancing Malus and Rubus organogenesis was related to the shoot proliferation activity of the cytokinin and to treatment-induced variation in leaf and petiole size.Abbreviations BA
benzyladenine
- 2,4-D
2,4-dichlorophenoxyacetic acid
- IBA
indolebutyric acid
- MS
Murashige & Skoog basal medium devoid of plant growth regulators
- OI
organogenesis-initiating subculture
- PTI
colchicine pretreatment subculture
- PTII
cytokinin pretreatment subculture
- NAA
naphthaleneacetic acid
- TDZ
thidiazuron
- zeatin
trans-zeatin 相似文献
195.
196.
197.
Across the world there is a prevailing view that freshwater algae are cosmopolitan. The notion has seldom been tested and
is unlikely to be true in genetic terms. Nonetheless, some morphospecies of several groups of algae do have a worldwide distribution.
Others have restricted distributions and may be regarded as endemic to a region. However there is always the possibility that
they will be discovered in far away places. Australia has a rather large element of endemicity in its algal flora. From the
early days of Australian phycology many new genera and species of freshwater algae have been described. Some are of such distinctive
appearance or novelty as to be regarded as ‘flagship’ taxa. There is little doubt about their endemicity and their existence
increases the probability of less-distinguished species also being endemic. The degree of endemicity is probably masked by
the ‘force-fitting’ of European names to Australian species.
Some Australian endemics are robust and are widely distributed in a variety of types of water body. Others, the frail endemics,
the ones of greatest novelty and phylogenetic significance, have a very restricted range with their strongholds in dystrophic
coastal lagoons where tracts or remnant patches of native vegetation survive. Their survival and the conservation of their
biodiversity depends on recognition of the significance of coastal lagoons and swamps. 相似文献
198.
Jan H. Mol 《Oecologia》1996,107(3):395-410
This study investigated the role of predators in preventing competitive exclusion among three closely related armoured catfishes (Callichthys callichthys, Hoplosternum littorale and H. thoracatum) that occur synthopically in multi-predator freshwater swamps of Suriname, South America. The potential impact of predation on armoured catfish was determined by combining laboratory measurements of predation rates on five early developmental stages of the armoured catfish H. thoracatum for 24 aquatic predators with field studies of the density of the predators in the swamps. The contribution of a particular predator to the total predation pressure on its prey was determined to a large extent by the density of the predator in the swamp. Seemingly innocuous predators with low or moderate predation rates in the laboratory may be extremely important in the swamps due to their high abundance. Small-sized omnivorous fishes and aquatic invertebrates were major predators of early developmental stages of armoured catfish. Both qualitative and quantitative ontogenetic changes in the predation pressure on armoured catfish were observed. Major predation on eggs, larvae and juveniles of H. thoracatum resulted from a different set of predators in each developmental stage of the prey. In all developmental stages of H. thoracatum the predation pressure involved several predator species and not a single, dominant predator. The potential predation pressure of the 24 predators taken together and the number of predators that were able to prey on H. thoracatum decreased sharply with increasing age (size) of the prey. Even if egg (nest) predation is prevented by the guarding male, the potential impact of the 24 predators on the populations of armoured catfish is large. Predation may account for the high mortality of H. thoracatum observed in the swamps. The high predation pressure on callichthyid catfishes may help to explain the coexistence of three closely related and morphologically quite similar armoured catfishes in Surinamese swamps. 相似文献
199.
Louise Warnich Peter N. Meissner Richard J. Hift Jan H. Louw Carel J. van Heerden Andries E. Retief 《Human genetics》1996,97(5):690-692
The gene for variegate porphyria (VP), an autosomal dominant disease with a high prevalence in South Africa, evidently due
to a founder effect, was previously mapped to chromosome 14q32. In the current study this localization was evaluated by linkage
and haplotype analyses using microsatellite markers spanning a region of more than 20 cM on chromosome 14q32. In many recent
studies linkage disequilibrium between disease and marker loci has been utilized to map genes in founder populations, but
we could not find any association between VP and the markers used in this study. Our data suggest that the allocation of VP
to chromosome 14q32 may be incorrect.
Received: 1 September 1995 / Revised: 1 November 1995 相似文献
200.
Grant E. Brown R. Jan F. Smith 《Ethology : formerly Zeitschrift fur Tierpsychologie》1996,102(5):776-785
Pike-naive fathead minnows (Pimephales promelas) were fed ad libitum or deprived of food for 12, 24, or 48 h and then exposed to either conspecific alarm pheromone or distilled water and the odour of a predatory northern pike (Esox lucius). Minnows fed ad libitum or deprived for 12 h showed a stereotypic alarm response to the alarm pheromone (increased time under cover objects and increased occurrence of dashing and freezing behaviour); those deprived of food for 24 h showed a significantly reduced alarm response, while those deprived of food for 48 h did not differ significantly from the minnows exposed to a distilled water control. Upon subsequent testing in an Opto-Varimex activity meter, all groups initially exposed to alarm pheromone and pike odour exhibited an alarm response when exposed to pike odour alone. Those initially conditioned with distilled water and pike odour did nor show an alarm response to pike odour alone. These results demonstrate that there exists a significant trade-off between hunger level and predator-avoidance behaviour in fathead minnows and that minnows can learn the chemical cues of a predatory northern pike through association with alarm pheromone even in the absence of an observable alarm response. 相似文献