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11.
Many microbial and cell cultures exhibit phenomena that can best be described using a segregated modeling approach. Heterogeneties are more marked in recombinant cell cultures because subpopulations, which often exhibit different growth and productivity characteristics, are more easily identified by selective markers. A simple segregated mathematical model that simulates the growth of recombinant Escherichia coli cells is developed. Subpopulations of different growth rate, plasmid replication rate, and plasmid segregation probability are explicitly considered. Results indicate that a third mechanism of plasmid instability, referred to here as a "downward selective pressure," is significant when describing plasmid loss in batch and chemostat cultures. Also, the model agrees well with experimental data from cultures under antibiotic selective pressure. Finally, model simulations of chemostat cultures reveal the importance of initial conditions on culture stability and the possible presence of nonrandom partitioning functions. (c) 1993 John Wiley & Sons, Inc. 相似文献
12.
Edna De la Llata Quiroga Randall Arauz Arturo Tripp Valdez Laura Porras Murillo Manuel Spinola Parallada Ricardo Sánchez-Murillo Elpis J. Chávez 《Journal of fish biology》2023,102(3):669-679
Bull shark (Carcharhinus leucas) is a near-threatened elasmobranch species capable of moving between the fresh and salty waters of tropical and subtropical coastal areas, for which we still lack important ecological information. During their first years of life, bull sharks use estuarine systems as nursery areas, making them highly susceptible to environmental and anthropogenic pressures. We studied the trophic ecology of juveniles found in the Coyote estuary, a potential nursery area in Costa Rica, to understand the potential impact of further bull shark declines and gain knowledge that could aid in their conservation. We analysed the trophic ecology of juvenile bull sharks [81–103 cm total length (TL)] in the Coyote estuary, Costa Rica, using stable isotopes of δ15N and δ13C. Since one problem using this technique in juveniles is the confounding effect of the maternal signature, we sampled different tissues (muscle and plasma), verified the status of the shark's umbilical scar and identified the size at which the isotope signature is a result of the animal's current diet. The isotopic values of the muscle tissue reflected the maternal isotopic signature. In contrast, plasma values reflected the diet of juvenile bull sharks >95 cm TL and with a closed umbilical scar. Juvenile bull sharks fed primarily on teleost fishes of the order Anguilliformes and Siluriformes, and have a high trophic position (≥4.0) in the Coyote estuary. Our findings suggest that this estuary is an important feeding site for juvenile bull sharks of the Pacific of Costa Rica. Thus, the protection of essential habitats such as the Coyote estuary will benefit not only bull shark conservation, but also the conservation of an array of fish species that also use this habitat as a rookery, many of which are of commercial interest. 相似文献
13.
Serrano Alejandra Kuhn Nathalie Restovic Franko Meyer-Regueiro Carlos Madariaga Mónica Arce-Johnson Patricio 《Journal of Plant Growth Regulation》2023,42(1):365-375
Journal of Plant Growth Regulation - Auxin is a hormone that delays ripening in part by reducing anthocyanin content and impairing color development. Auxin content declines during the ripening... 相似文献
14.
Eduardo R. Quiroga 《Human ecology: an interdisciplinary journal》1984,12(2):183-201
Experience with irrigation schemes designed to improve the productivity of subsistence farmers in Latin America seems to parallel the results of the green revolution in Southeast Asia. Although in some cases the impact on the productivity has been significant, in far too many cases the pervasive pattern of inequity has been reinforced. This case study of the Irrigation District of Zapotitan in El Salvador analyses some of the reasons for the unexpected results, with particular reference to the planning process. It essentially illustrates that the transformation of subsistence agriculture through irrigation demands new institutions designed not only to service agricultural production but also to ensure the accrual of benefits on the targeted group. 相似文献
15.
M López-Torres R Pérez-Campo C Rojas C Barja de Quiroga 《Revista Espanola de Fisiología》1992,48(3):191-196
Lipid peroxidation in rat liver and brain has been studied to see if it increases with old age. No significant differences in the level of endogenous, nonstimulated lipid peroxidation (TBA-RS) is found between 9 month-old (mature adults) and 28 month-old animals in liver or cerebral cortex. Liver homogenates subjected in vitro to an oxidative stress (ascorbate-Fe++), show a clearly slower peroxidation rate in old than in young animals. On the other hand, the in vitro peroxidation rate of cerebral homogenates was similar in young and old animals. The in vitro peroxidation rate was much higher in brain than in liver tissue. These results do not support the view that old rats liver and brain are more susceptible to free radical oxidative damage than those of young ones. 相似文献
16.
Barbara Maichak de Carvalho Alejandra Vanina Volpedo Cristiano Queiroz Albuquerque Luís Fernando Fvaro 《Zeitschrift fur angewandte Ichthyologie》2019,35(6):1286-1291
Sagitta otoliths are usually formed of calcium carbonate polymorphs as aragonite. The objective of this study was to verify which carbonate polymorph is predominant in the sagitta otolith of Menticirrhus americanus and check whether this pattern remains in otoliths with morphological alterations. Otoliths of M. americanus were obtained from five sites on the southeast‐south coast of Brazil (São Sebastião (SS) 23°45′S–45°24′O, n = 29; Cananéia‐Iguape Estuarine Complex (CI) 25°02′S–47°54′O, n = 30; Paranaguá Estuarine Complex (PEC) 25°28′S–48°20′O, n = 35; Itapoá (IT) 26°07′S–48°36′O, n = 31; Laguna (LA) 28°28′S–48°46′O, n = 13). The characterization of carbonate polymorphs of otoliths was performed through Raman spectroscopy, a photonic and non‐destructive technique that analyzes molecular vibrations induced by laser. We analyzed 138 pairs of M. americanus otoliths, of which eight otoliths from different pairs presented morphological alterations (SS n = 1, CEP n = 5, IT n = 1, LA n = 1). The Raman spectra show that normal otoliths, that is, without morphological alterations, presented only aragonite in their structure. Among the otoliths that presented morphological alterations, the Raman spectra allowed to identify in six otoliths the deposition of aragonite and in only two otoliths the deposition of vaterite (one specimen of the PEC and one of SS). 相似文献
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18.
群落的多样性取决于物种相互共存的能力,以及克服环境胁迫的能力,从而可能扮演一个环境过滤器的角色。生态位分化导致了比种间竞争更强的种内竞争,促进了物种共存。由于胁迫影响相互作用,生态位分化的强度可能沿胁迫作用的梯度发生变化。在有胁迫的栖息地,如沙漠和高山地区,植物的生长形式更加多样化,这表明在环境胁迫下植物具有更强的生态位分化。我们验证了生态位差异和环境过滤作用随着环境胁迫的增加而增强的假设。在墨西哥南部的半干旱草原上,我们沿着水分胁迫梯度在田间种植了6种一年生植物。植物进行三种种植处理:单独种植(没有相互作用),与同种植物为邻(种内相互作用)或与异种植物为邻(种间相互作用)。我们分析了种内与种间竞争的比值是如何沿水分胁迫梯度变化的,以评估水分如何决定生态位分化的强度。我们还测定了水分胁迫是否代表了一种环境过滤作用。我们发现了种内竞争比种间竞争更强,尤其是在水分胁迫更大的情况下。因此,我们的结果表明,除了一个物种外,所有物种至少在部分水分胁迫梯度下存在生态位分化。一些物种受到胁迫的阻碍,而另一些物种可能因为胁迫消除了土壤病原体而受到它的青睐。虽然高强度的生态位分化在环境胁迫下出现的频率略高,但由于我们的物种样本很小,而且这种通用的模式也存在例外,因此需要进一步的研究来确定这是否是自然界普遍存在的现象。 相似文献
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20.
Mayarling Francisca Troncoso Jafet Ortiz-Quintero Valeria Garrido-Moreno Fernanda Sanhueza-Olivares Alejandra Guerrero-Moncayo Mario Chiong Pablo F. Castro Lorena García Luigi Gabrielli Ramón Corbalán Luis Garrido-Olivares Sergio Lavandero 《生物化学与生物物理学报:疾病的分子基础》2021,1867(9):166170
The vascular cellular adhesion molecule-1 (VCAM-1) is a protein that canonically participates in the adhesion and transmigration of leukocytes to the interstitium during inflammation. VCAM-1 expression, together with soluble VCAM-1 (sVCAM-1) induced by the shedding of VCAM-1 by metalloproteinases, have been proposed as biomarkers in immunological diseases, cancer, autoimmune myocarditis, and as predictors of mortality and morbidity in patients with chronic heart failure (HF), endothelial injury in patients with coronary artery disease, and arrhythmias. This revision aims to discuss the role of sVCAM-1 as a biomarker to predict the occurrence, development, and preservation of cardiovascular disease. 相似文献