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141.
Peroxidase activity and isoenzyme pattern were investigated in buds and tubers of Jerusalem artichokes in relation to induction and breaking of dormancy. Peroxidase activity per unit soluble protein is the highest in the dormant stage. Conditions leading to growth,i.e. release of dormancy by the cold, stimulation of axial growth by gibberellic acid or stimulation of radial growth (tuberization) by kinetin, cause rapid loss of total peroxidase activity together with a decrease of intensity of the most cathodic isoperoxidases. Induction of dormancy by AMO-1618 increases peroxidase activity mainly through the same cathodic isoenzymes. The role of the cathodic isoperoxidases is discussed in relation to auxin catabolism and the genesis of oxygenation products inhibitory to plant growth. 相似文献
142.
Habituated sugarbeet callus examined by means of a light-microscope is characterized by absence of differentiated tracheary
elements and of the reaction with syringaldazine. Habituated tissues also were found to exhibit low guaiacol- and syringaldazine-peroxidase
activities, a deficiency of lignin as well as lower cellulose, dry mass and chlorophyll contents as compared to the normal
auxin-requiring callus. These histological and cytological features led to consider this habituated callus as a vitrified
tissue under stress. The question of a relationship between vitrification and habituation is posed. 相似文献
143.
N G Seidah L Gaspar P Mion M Marcinkiewicz M Mbikay M Chrétien 《DNA and cell biology》1990,9(6):415-424
Based on the concept of sequence conservation around the active sites of serine proteinases, polymerase chain reaction applied to mRNA amplification allowed us to obtain a 260-bp probe which was used to screen a mouse pituitary cDNA library. The primers used derived from the cDNA sequence of active sites Ser* and Asn* of human furin. Two cDNA sequences were obtained from a number of positive clones. These code for two similar but distinct structures (mPC1 and mPC2), each being homologous to yeast Kex2 and human furin. In situ hybridization (mPC1) and Northern blots (mPC1 = 3.0 kb and mPC2 = 2.8 and 4.8 kb) demonstrated tissue and cellular specificity of expression, only within endocrine and neuroendocrine cells. These data suggest that mPC1 and mPC2 represent prime candidates for tissue-specific pro-hormone converting proteinases. 相似文献
144.
145.
Pascal Lambé Hity Schié Nkung Mutambel Jean-Gabriel Fouché Roger Deltour Jean-Michel Foidart Thomas Gaspar 《In vitro cellular & developmental biology. Plant》1997,33(3):155-162
Summary Progressive loss of organogenic totipotency appears to be a common event in long-term plant tissue culture. This loss of totipotency,
which has been proposed to be a typical trait of plant neoplastic progression, is compared to some mechanisms that occur during
the establishment of animal differentiation-resistant cancer lines in vitro. Evidence is presented that alteration in DNA methylation patterns and expression of genes occur during long-term callus
culture. An effect of the auxin, 2,4-dichlorophenoxyacetic acid, in the progressive methylation, is moreover suggested. Methylation
of genes relevant to cell differentiation and progressive elimination of cells capable of differentiation is proposed as being
responsible for this progressive loss of organogenic potential. Finally, the epigenetic alteration (DNA methylation) that
occurs during prolonged periods of culture may induce other irreversible genetic alterations that ultimately make the loss
of totipotency irreversible. 相似文献
146.
Ana S. Fernandes João Serejo Jorge Gaspar Fátima Cabral Ana F. Bettencourt José Rueff Matilde Castro Judite Costa Nuno G. Oliveira 《Cell biology and toxicology》2010,26(2):91-101
Oxidative cell injury could be induced by different reactive oxygen species (ROS) operating in multiple pathways. The present
work is focused on three different models of oxidative stress: the xanthine/xanthine oxidase system (XXO), an extracellular
superoxide anion generator; tert-butylhydroperoxide (TBHP), an analogue of lipid hydroperoxides; and doxorubicin (Dox), an anticancer drug. Superoxide and
peroxyl radicals, among other ROS, could be effectively scavenged by MnTM-4-PyP, a polyfunctional catalytic antioxidant. In
this report, we have addressed the role of MnTM-4-PyP on the protection against the cytotoxicity induced by the three aforementioned
oxidants. The effect of MnTM-4-PyP (0.1–100 μM) was evaluated in V79 fibroblasts using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide reduction and the crystal violet assays, as well as the mitotic index. Also, the generation of intracellular
ROS was studied by the fluorescent probe dihydroethidium. MnTM-4-PyP has shown significant protective effects against the
cytotoxicity of XXO and TBHP, increasing the cell viability in approximately 40% and reducing the intracellular level of ROS.
However, no considerable protection occurred against Dox. The three oxidants caused a mitotic index reduction that was not
altered by MnTM-4-PyP. In summary, MnTM-4-PyP appears to be a promising agent for the protection against oxidative injury.
However, it has shown differential responses, reinforcing the need to study different experimental models for the adequate
evaluation of its potentialities as a catalytic antioxidant. 相似文献
147.
148.
Monserrat JM Martínez PE Geracitano LA Amado LL Martins CM Pinho GL Chaves IS Ferreira-Cravo M Ventura-Lima J Bianchini A 《Comparative biochemistry and physiology. Toxicology & pharmacology : CBP》2007,146(1-2):221-234
In this review, recent developments in monitoring toxicological responses in estuarine animals are analyzed, considering the biomarker responses to different classes of pollutants. The estuarine environment imposes stressful conditions to the organisms that inhabit it, and this situation can alter their sensitivity to many pollutants. The specificity of some biomarkers like metallothionein tissue concentration is discussed in virtue of its dependence on salinity, which is highly variable in estuaries. Examples of cholinesterase activity measurements are also provided and criteria to select sensitive enzymes to detect pesticides and toxins are discussed. Regarding non-specific biomarkers, toxic responses in terms of antioxidant defenses and/or oxidative damage are also considered in this review, focusing on invertebrate species. In addition, the presence of an antioxidant gradient along the body of the estuarine polychaete Laeonereis acuta (Nereididae) and its relationship to different strategies, which deal with the generation of oxidative stress, is reviewed. Also, unusual antioxidant defenses against environmental pro-oxidants are discussed, including the mucus secreted by L. acuta. Disruption of osmoregulation by pollutants is of paramount importance in several estuarine species. In some cases such as in the estuarine crab Chasmagnathus granulatus, there is a trade off between bioavailability of toxicants (e.g. metals) and their interaction with key enzymes such as Na(+)-K(+)-ATPase and carbonic anhydrase. Thus, the metal effect on osmoregulation is also discussed in the present review. Finally, field case studies with fish species like the croaker Micropogonias furnieri (Scianidae) are used to illustrate the application of DNA damage and immunosuppressive responses as potential biomarkers of complex mixture of pollutants. 相似文献
149.
TSSA (trypomastigote small surface antigen) is a polymorphic mucin-like molecule displayed on the surface of Trypanosoma cruzi trypomastigote forms. To evaluate its functional properties, we undertook comparative biochemical and genetic approaches on isoforms present in parasite stocks from extant evolutionary lineages (CL Brener and Sylvio X-10). We show that CL Brener TSSA, but not the Sylvio X-10 counterpart, exhibits dose-dependent and saturable binding towards non-macrophagic cell lines. This binding triggers Ca(2+)-based signalling responses in the target cell while providing an anchor for the invading parasite. Accordingly, exogenous addition of either TSSA-derived peptides or specific antibodies significantly inhibits invasion of CL Brener, but not Sylvio X-10, trypomastigotes. Non-infective epimastigote forms, which do not express detectable levels of TSSA, were stably transfected with TSSA cDNA from either parasite stock. Although both transfectants produced a surface-associated mucin-like TSSA product, epimastigotes expressing CL Brener TSSA showed a ~2-fold increase in their attachment to mammalian cells. Overall, these findings indicate that CL Brener TSSA functions as a parasite adhesin, engaging surface receptor(s) and inducing signalling pathways on the host cell as a prerequisite for parasite internalization. More importantly, the contrasting functional features of TSSA isoforms provide one appealing mechanism underlying the differential infectivity of T. cruzi stocks. 相似文献
150.