Effect of hyperoxide radicals on bovine-erythrocyte membrane.

1. Bovine erythrocytes exposed to the action of an enzymic source of hyperoxide radicals (hypoxanthine + xanthine oxidase) exhibited hemolysis, which was prevented by the presence of hyperoxide dismutase. 2. Exposing bovine erythrocyte membranes to the source of hyperoxide radicals resulted in a decrease of (Mg2+ + Na+ + K+)ATPase activity which could be partially prevented by addition of hyperoxide dismutase. 3. The damage observed to erythrocyte membranes under the conditions applied is ascribed to toh formed in the Haber and Weiss reaction since a protection by OH scavengers was also observed.     

Hemoglobin can nitrate itself and other proteins.

Incubation of human hemoglobin with nitrite and hydrogen peroxide was found to induce autonitration and nitration of another protein (bovine serum albumin), as demonstrated by detection of nitrotyrosine residues in Western blots of separated membrane proteins. Inhibition of nitration by conversion of hemoglobin into the cyanmet form demonstrates that nitration is due to the pseudoperoxidase activity of hemoglobin. Incubation of whole erythrocytes with nitrite and hydrogen peroxide induces nitration of erythrocyte membrane proteins, much stronger when cellular catalase was inhibited with azide. These results suggest that hemoglobin and other hemoproteins may contribute to the tyrosine nitration in vivo.     

Hold your breath beetle—Mites!

Respiratory gas exchange in insects occurs via a branching tracheal system. The entrances to the air‐filled tracheae are the spiracles, which are gate‐like structures in the exoskeleton. The open or closed state of spiracles defines the three possible gas exchange patterns of insects. In resting insects, spiracles may open and close over time in a repeatable fashion that results in a discontinuous gas exchange (DGE) pattern characterized by periods of zero organism‐to‐environment gas exchange. Several adaptive hypotheses have been proposed to explain why insects engage in DGE, but none have attracted overwhelming support. We provide support for a previously untested hypothesis that posits that DGE minimizes the risk of infestation of the tracheal system by mites and other agents. Here, we analyze the respiratory patterns of 15 species of ground beetle (Carabidae), of which more than 40% of individuals harbored external mites. Compared with mite‐free individuals, infested one's engaged significantly more often in DGE. Mite‐free individuals predominantly employed a cyclic or continuous gas exchange pattern, which did not include complete spiracle closure. Complete spiracle closure may prevent parasites from invading, clogging, or transferring pathogens to the tracheal system or from foraging on tissue not protected by thick chitinous layers.     

Integument cell gelatinisation—the fate of the integumentary cells in <Emphasis Type="Italic">Hieracium</Emphasis> and <Emphasis Type="Italic">Pilosella</Emphasis> (Asteraceae)

Members of the genera Hieracium and Pilosella are model plants that are used to study the mechanisms of apomixis. In order to have a proper understanding of apomixis, knowledge about the relationship between the maternal tissue and the gametophyte is needed. In the genus Pilosella, previous authors have described the specific process of the “liquefaction” of the integument cells that surround the embryo sac. However, these observations were based on data only at the light microscopy level. The main aim of our paper was to investigate the changes in the integument cells at the ultrastructural level in Pilosella officinarum and Hieracium alpinum. We found that the integument peri-endothelial zone in both species consisted of mucilage cells. The mucilage was deposited as a thick layer between the plasma membrane and the cell wall. The mucilage pushed the protoplast to the centre of the cell, and cytoplasmic bridges connected the protoplast to the plasmodesmata through the mucilage layers. Moreover, an elongation of the plasmodesmata was observed in the mucilage cells. The protoplasts had an irregular shape and were finally degenerated. After the cell wall breakdown of the mucilage cells, lysigenous cavities that were filled with mucilage were formed.     

A role for yeast glutaredoxin genes in selenite-mediated oxidative stress

Since the double Δgrx1Δgrx2 mutant is hypersensitive to selenite we decided to evaluate mechanisms underlying this phenomenon and establish the roles of other components of yeast glutaredoxin system, in particular glutaredoxin 5 in the selenite resistance. We found elevation in the intracellular and mitochondrial superoxide production in the Δgrx1Δgrx2 and Δgrx5 mutants after Se(IV) treatment. The last effect was more pronounced for cells lacking the mitochondrial Grx5 protein. We also recorded selenite-induced increase in the peroxide production in all strains tested. Nonfermentable carbon sources, glycerol and ethanol, augmented selenite toxicity. Hypo- and anoxia protected against the harmful effects of Se(VI). Augmentation of the intracellular levels of two endogenous antioxidants, erythroascorbic acid and glutathione confers resistance to selenite. We recorded a strain-unspecific, selenite-mediated decrease in the level of acid-soluble thiols. Collectively, our data demonstrate that hypersensitivity to the Δgrx1Δgrx2 and Δgrx5 disruptants to selenite is mediated by altered intracellular redox equilibrium.