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排序方式: 共有347条查询结果,搜索用时 887 毫秒
41.
This study evaluated the reproductive features of Octopus tehuelchus in three coastal environments of San Matías Gulf (Patagonia). Monthly samples of O. tehuelchus were used to estimate size at maturity, compare seasonal changes in oocyte size frequency distributions between sites as well as oocyte number and size between female maturity stage and sites. Females in Islote Lobos had a smaller size at maturity than females in San Antonio Bay and El Fuerte, probably as a consequence of a generally smaller body size. Males in San Antonio Bay were smaller at maturity than females. O. tehuelchus is a simultaneous terminal spawner. Fecundity (expressed as number of vitellogenic oocytes in ovary) was lower in Islote Lobos, and an increase in oocyte number in relation to female total weight was found. Females in San Antonio Bay had the largest oocytes, which may indicate higher energy reserves for the embryo and therefore higher juvenile survival. There was a close relationship between reproduction, growth and condition, represented as size at maturity, number and size of vitellogenic oocytes and period of maturity and spawning. Given the local variation in some reproductive features of O. tehuelchus, studies should focus on the environmental factors, which bring about this variation, and on how it affects the dynamics of local populations. 相似文献
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43.
Development of alcoholic and malolactic fermentations in highly acidic and phenolic apple musts 总被引:2,自引:0,他引:2
This work reports the influence of the high acidity and high phenolic content in apple musts on the development of alcoholic and malolactic fermentations and on the final chemical and microbiological composition of the ciders. Four different musts were obtained by pressing several varieties and proportions of cider apples from the Basque Country (Northern Spain). Specially acidic and phenolic varieties were selected. Three musts were obtained in experimental stations and the fourth one, in a cider factory following usual procedures. The evolution of these musts was monitored during five months by measuring 18 parameters throughout eight samplings. In the most acidic of the three experimental musts, yeasts were added to complete the alcoholic fermentation. In the rest of the musts, alcoholic and malolactic fermentations took place spontaneously due to natural microflora and no chemical was added to control these processes. Malolactic fermentation (MLF) finished before alcoholic fermentation in the three tanks obtained in experimental stations, even in the most acidic and phenolic one (pH 3.18, 1.78 g tannic acid/l). After four months, these ciders maintained low levels of lactic acid bacteria (10(4)CFU/ml) and low content of acetic acid (<0.60 g/l). Both fermentations began simultaneously in the must obtained in the cider factory, but MLF finished 10 days after alcoholic fermentation. Subsequently, this must maintained a high population of lactic acid bacteria (>10(6)CFU/ml), causing a higher production of acetic acid (>1.00 g/l) than in the other ciders. These results show the possible advantages of MLF finishing before alcoholic fermentation. 相似文献
44.
The ability of Urografin or Percoll density gradient centrifugations to separate nonculturable subpopulations from heterogeneous
Escherichia coli populations was analysed. Bacterial counts (total, active and culturable cells) and flow cytometric analyses were carried
out in all recovered bands. After Urografin centrifugation, and despite the different origin of E. coli populations, a common pattern was obtained. High-density bands were formed mainly by nonculturable cells. However, the increase
in cell density would not be common to all nonculturable cells, since part of this subpopulations banded in low-density zones,
mixed with culturable cells. Bands obtained after Percoll centrifugation were heterogeneous and culturable and nonculturable
cells were recovered along the gradient. Thus, fractionation in Urografin cannot be only attributed to changes in buoyant
densities during the transition from culturable to nonculturable state. Urografin density gradients allow us to obtain enriched
fractions in nonculturable subpopulations from a heterogeneous population, but working conditions should be carefully chosen
to avoid Urografin toxicity. 相似文献
45.
Bacteriophages infecting Bacteroides fragilis strains RYC2056 and HSP40 have been proposed as indicators of water quality. To accomplish this function, homogeneity of
the group of phages detected by these strains is necessary to ensure that the final results are not due to the different kinetics
of inactivation of the phages. To evaluate homogeneity, we observed by electron microscopy bacteriophages isolated from sewage
with two Bacteroides fragilis strains (HSP40 and RYC2056). A predominant group of phages was observed, Siphoviridae with slightly curved tails. Detection of other minority groups, which could be present in the sample, was done with neutralization
experiments by using antiserum against the majority group and with host mutants resistant to infection with the predominant
phage. Although two other minority groups were observed, results showed that bacteriophages infecting B. fragilis strain HSP40 and strain RYC2056 form a homogeneous group, Siphoviridae with slightly curved tails being the most predominant in sewage.
Received: 7 March 2002 / Accepted: 5 August 2002 相似文献
46.
Maite Solas Bárbara Aisa Rosa M. Tordera María C. Mugueta María J. Ramírez 《生物化学与生物物理学报:疾病的分子基础》2013,1832(12):2332-2339
It is becoming evident that chronic exposure to stress not only might result in insulin resistance or cognitive deficits, but may also be considered a risk factor for pathologies such as depression or Alzheimer's disease (AD). There is great interest in determining the molecular mechanisms underlying interactions between stress, aging, memory and Alzheimer's disease (AD). We have used the chronic mild stress (CMS) model to study the effects of chronic stress on the aging process and the development of central insulin resistance and AD pathology. CMS aged mice showed cognitive impairments in the novel object recognition test. In addition, CMS aged mice displayed both peripheral insulin resistance, as shown by HOMA index, and decreased hippocampal levels of pIRS and downstream intracellular signaling (pAKT, pGSK and pERK1/2). Interestingly, there was a significant increase in both C99:C83 ratio and BACE1 levels in the hippocampus of CMS aged mice. Increased expression of the AD marker pTau was also found in stressed aged mice. Increased expression of the stress-activated protein kinase JNK was found in CMS aged mice, accompanied by significant decreases in glucocorticoid receptor (GR) expression and increases in mineralocorticoid receptor (MR) expression. It is suggested that the interaction of stress with aging should be considered when studying determinants of the onset and progression of AD. 相似文献
47.
Depopulation of rural areas is a widespread phenomenon that has occurred in most industrialized countries, and has contributed significantly to a reduction in the productivity of agro-ecological resources. In this study, we identified the main trends in the dynamics of rural populations in the Central Pyrenees in the 20th C and early 21st C, and used density independent and density dependent models and identified the main factors that have influenced the dynamics. In addition, we investigated the change in the power law distribution of population size in those periods. Populations exhibited density-dependent positive feedback between 1960 and 2010, and a long-term positive correlation between agricultural activity and population size, which has resulted in a free-scale population distribution that has been disrupted by the collapse of the traditional agricultural society and by emigration to the industrialized cities. We concluded that complex socio-ecological systems that have strong feedback mechanisms can contribute to disruptive population collapses, which can be identified by changes in the pattern of population distribution. 相似文献
48.
49.
Marianela Gastaldi Thiago S. De Paula Maite A. Narvarte Gisele Lôbo-Hajdu Eduardo Hajdu 《Marine Biology Research》2018,14(7):682-716
Six sponge species from Bahía San Antonio (north Argentinean Patagonia) are (re)described, including two new species, namely Halichondria (Halichondria) elenae sp. nov. and Clathria (Microciona) saoensis sp. nov., and three new records for the Argentinean coast. Halichondria (H.) elenae sp. nov. is the only yellowish-greenish SW Atlantic Halichondria with oxeas up to 450?µm. The new species’ 18S rRNA blasted with Halichondria bowerbanki from Ireland, but it is argued that co-specificity is unlikely, in view of their rather distinct morphologies. Clathria (M.) saoensis sp. nov. is the only C. (Microciona) in the SW Atlantic, SE Pacific, and (sub)Antarctic regions with smooth (or nearly so) principal megascleres, mostly below 500?µm long, as well as moderately curved toxas, and isochelae of regular non-cleistochelate shape. Cliona aff. celata and Hymeniacidon perlevis had their identifications confirmed by the sequencing of their 28S and 18S rRNA genes, respectively, and mitochondrial CO1. Both of them clustered with previously sequenced specimens from the Temperate North Atlantic, apart from additional samples from SE Brazil, in the case of C. aff. celata, and China and South Korea, in the case of H. perlevis. 相似文献
50.
Maite Lacuesta Iñigo Saiz-Fernández Kateřina Podlešáková Jon Miranda-Apodaca Ondřej Novák Karel Doležal Nuria De Diego 《Plant Growth Regulation》2018,85(2):199-209
Abscisic acid (ABA), auxins, and cytokinins (CKs) are known to be closely linked to nitrogen signaling. In particular, CKs control the effects of nitrate availability on plant growth. Our group has shown that treatment with high nitrate concentrations limits root growth and leaf development in maize, and conditions the development of younger roots and leaves. CKs also affect source-sink relationships in plants. Based on these results, we hypothesized that CKs regulate the source-sink relationship in maize via a mechanism involving complex crosstalk with the main auxin indole-3-acetic acid (IAA) and ABA. To evaluate this hypothesis, various CK metabolites, IAA, and ABA were quantified in the roots and in source and sink leaves of maize plants treated with high and normal nitrate concentrations. The data obtained suggest that the cis and trans isomers of zeatin play completely distinct roles in maize growth regulation by a complex crosstalk with IAA and ABA. We demonstrate that while trans-zeatin (tZ) and isopentenyladenine (iP) regulate nitrate uptake and thus control final leaf sizes, cis-zeatin (cZ) regulates source and sink strength, and thus controls leaf development. The implications of these findings relating to the roles of ABA and IAA in plants’ responses to varying nitrate concentrations are also discussed. 相似文献