ascorbic-acid and (3-4-dihydroxyphenylamino)-2-imidazoline

Reactive oxygen intermediates, i.e. the superoxide radical (O*-)(2), hydrogen peroxide (H2O2) and the hydroxyl radical (*OH), are generally regarded as harmful products of oxygenic metabolism causing cell damage in plants, animals and microorganisms. However, oxygen radical chemistry may also play a useful role in polymer breakdown leading to wall loosening during extension growth of plant cells controlled by the phytohormone auxin. Backbone cleavage of cell wall polysaccharides can be accomplished in vitro by (*OH) produced from H2O2 in a Fenton reaction or in a reaction catalyzed by peroxidase supplied with O2 and NADH. Here, we show that coleoptile growth of maize seedlings is accompanied by the release of reactive oxygen intermediates in the cell wall. Auxin promotes release of (O*-)(2) and subsequent generation of (*OH)when inducing elongation growth. Experimental generation of (*OH) in the wall causes an increase in wall extensibility in vitro and replaces auxin in inducing growth. Auxin-induced growth can be inhibited by scavengers of (O*-)(2), H2O2 or (*OH), or inhibitors interfering with the formation of these molecules in the cell wall. These results provide the experimental background for a novel hypothesis on the mechanism of plant cell growth in which (*OH), produced from (O*-)(2) and H2O2 by cell wall peroxidase, acts as a wall-loosening agent.

Topics: 2,4-Dichlorophenoxyacetic Acid; Ascorbic Acid; Benzoates; Catecholamines; Cell Wall; Cotyledon; Deferoxamine; Hydrogen Peroxide; Hydroxyl Radical; Imidazolines; Indoleacetic Acids; NAD; NADP; Naphthaleneacetic Acids; Organometallic Compounds; Oxygen; Reactive Oxygen Species; Superoxide Dismutase; Superoxides; Zea mays

Oxidized low density lipoprotein (ox-LDL) has been suggested to affect endothelium-dependent vascular tone through a decreased biological activity of endothelium-derived nitric oxide (NO). Oxidative inactivation of NO is regarded as an important cause of its decreased biological activity, and in this context superoxide (O(2)) is known to inactivate NO in a chemical reaction during which peroxynitrite is formed. In this study we examined the effect of ox-LDL on the intracellular NO concentration in bovine aortic endothelial cells and whether this effect is influenced by ox-LDL binding to the endothelial receptor lectin-like ox-LDL receptor-1 (LOX-1) through the formation of reactive oxygen species and in particular of O(2). ox-LDL induced a significant dose-dependent decrease in intracellular NO concentration both in basal and stimulated conditions after less than 1 min of incubation with bovine aortic endothelial cells (p < 0.01). In the same experimental conditions ox-LDL also induced O(2) generation (p < 0.001). In the presence of radical scavengers and anti-LOX-1 monoclonal antibody, O(2) formation induced by ox-LDL was reduced (p < 0.001) with a contemporary rise in intracellular NO concentration (p < 0.001). ox-LDL did not significantly modify the ability of endothelial nitric oxide synthase to metabolize l-arginine to l-citrulline. The results of this study show that one of the pathophysiological consequences of ox-LDL binding to LOX-1 may be the inactivation of NO through an increased cellular production of O(2).

Topics: Allopurinol; Animals; Antibodies, Monoclonal; Antioxidants; Aorta; Ascorbic Acid; Aspirin; Bradykinin; Catecholamines; Cattle; Cells, Cultured; CHO Cells; Chromans; Cricetinae; Dose-Response Relationship, Drug; Endothelium, Vascular; Enzyme Inhibitors; Flow Cytometry; Free Radical Scavengers; Hemostatics; Humans; Imidazolines; Lipoproteins, LDL; Mice; Nitric Oxide; omega-N-Methylarginine; Oxygen; Probucol; Protein Binding; Reactive Oxygen Species; Receptors, LDL; Receptors, Oxidized LDL; Scavenger Receptors, Class E; Superoxides; Thrombin; Time Factors