Cadmium and zinc-mediated oxidative burst in tobacco BY-2 cell suspension cultures

Generation of reactive oxygen species (ROS) constitutes an important first reaction under many stress conditions in plants. We demonstrate that Nicotiana tabacum L. cv. Bright Yellow 2 (TBY-2) cells in suspension cultures, generate superoxide radical and hydrogen peroxide upon treatment with cadmium and zinc. Addition of catalase and N,N-diethyldithiocarbamate (DDC) decreased the level of H₂O₂, whereas superoxide dismutase (SOD) induced a slight increase of the H₂O₂ production. The effects of catalase, DDC and SOD on the heavy metal-induced ROS production indicate that it occurs outside of the cells, and that at least part of the hydrogen peroxide is produced by dismutation of the superoxide radical (O₂ ^·−). The effect of pretreatment of the cell cultures with commonly used mammalian NADPH oxidase inhibitors was also tested. Strong inhibitions of cadmium and zinc-mediated ROS production were obtained with the flavoprotein inhibitors—diphenylene iodonium (DPI) and quinacrine and with an inhibitor of b-type cytochromes—imidazol. Membrane permeable-N-ethyl maleimide (NEM) and iodoacetate, and membrane non-permeable thiol reagents—para-chloromercuribenzoic acid (pCMBS) also inhibited the ROS production. These results suggested that the enzyme responsible for cadmium and zinc-induced ROS production in tobacco cells contains a flavocytochrome. They also show the importance of intra- and extracellular thiol groups in the observed stress reaction. The induction of ROS production with heavy metals showed properties comparable to the elicitor-induced oxidative burst in other plant cells.     

Cytoplasmic 3H-arginine polypeptides of Ehrlich ascites tumour cells

Summary Low molecular weight ninhydrin positive peptide fractions of the Ehrlich tumour cell cytoplasm were isolated and characterized. After preliminary gel filtration of the cytoplasm on Sephadex G-25 column, the peptide mixture was fractionated on cationic exchanger SP-Sephadex C-25 column and eluted with increasing pH gradient. Five peaks were obtained. Only the first peak contained sugar component. All five peptides were studied with respect to molecular weight, isoelectric point and electrophoretic homogeneity. The cytoplasm of Ehrlich tumour cells contains one peptide of acidic (pI - 5.0), two slightly basic (pI - 7.7 and pI - 7.7) and two strongly basic nature (pI - 8.7 and pI - 8.9). Molecular weights varied from 8 500 to 18 500 daltons. The origin of these peptides is briefly discussed.     

Benthic feeding by krill, Euphausia superba Dana, in coastal waters off West Antarctica and in Admiralty Bay, South Shetland Islands

Diatoms in the food of krill caught in the summer in coastal waters close to the South Shetland Islands and in the summer and three winters in Admiralty Bay, King George Island were investigated. The diatoms were used as indicators of sources of krill food. Principal component analysis divided the diatom taxa into two groups, one being pelagic diatoms and from the food of krill in coastal waters, and the other being benthic diatoms and taxa from the food of krill in Admiralty Bay. All pelagic taxa of diatoms were consumed by krill. In the summer in coastal waters, benthic diatoms in krill food originated from the sublittoral. In the summer in Admiralty Bay, besides phytoplankton, diatoms were noted from the sublittoral and littoral in the food of krill. However, in the winter mostly sublittoral and epiphytic diatoms were present in krill food. Accepted: 20 March 2000     

MetaMQAP: A meta-server for the quality assessment of protein models

Background  

Computational models of protein structure are usually inaccurate and exhibit significant deviations from the true structure. The utility of models depends on the degree of these deviations. A number of predictive methods have been developed to discriminate between the globally incorrect and approximately correct models. However, only a few methods predict correctness of different parts of computational models. Several Model Quality Assessment Programs (MQAPs) have been developed to detect local inaccuracies in unrefined crystallographic models, but it is not known if they are useful for computational models, which usually exhibit different and much more severe errors.     

Winter food caches of beavers<Emphasis Type="Italic">Castor fiber</Emphasis> in NE Poland

Winter food caches of beaversCastor fiber Linnaeus, 1758 were examined in 16 locations within the Suwałki region (north-eastern Poland). Four caches were selected to represent each of four habitat types: river, lake, farmland, and oligotrophic small reservoir called ‘suchar’. Altogether, 92 509 twigs and branches of 15 woody species were identified and measured. Individual caches, with one exception, included branches of only 4 or 5 species. WillowsSalix sp., birchesBetula sp., alderAlnus glutinosa, trembling aspenPopulus tremula, and mountain ashSorbus aucuparia occurred in caches from all four habitats studied. Willows alone constituted 62.5% of the total number of branches cached. Willows, together with birch, hazelCorylus avellana, alder, and trembling aspen, amounted to 97% of all branches in caches. The remaining 10 species provided only 3% of the branches cached. Most branches were 0.5–1 m long and <3 cm thick at their base. Contents of food caches provided a good indication of winter diet and possibly food preference of beavers.     

DNA-protein cross-linking in L1210 cells sensitive and resistant to cis-diamminedichloroplatinum (II)

The role of restricted cellular accumulation of cis-diamminedichloroplatinum(II) (cis-DDP) and altered repair of DNA-Pt-protein cross-links in the mechanism of L1210 murine leukemia cell resistance was examined. An immunochemical method was used to analyze the formation and removal of DNA-Pt-protein complexes in L1210 cells sensitive and resistant to cis-DDP. The accumulation of Pt into the cells and the binding of Pt to the DNA was measured by atomic absorption spectroscopy. The results demonstrated that both decreased accumulation of the drug and the rate of DNA-Pt protein cross-link removal may be important factors in L1210 cell resistance to cis-DDP.Abbreviations AAS atomic absorption spectroscopy - cis-DDP cis-diamminedichloroplatinum(II)