Elevated Oxygen Levels Research Articles

GERMINATION RESPONSES TO LIGHT AND ALTERNATING TEMPERATURES IN EUROPEAN POPULATIONS OF DACTYLIS GLOMERATA L.

SummaryThe influence of the outer covering structures (palea, lemma and pericarp) on the germination response to light and alternating temperatures was investigated in two populations of Dactylis glomerata L. Removal of the palea and lemma was less effective than light or alternating temperatures in promoting germination. Despite quantitative differences, both populations responded similarly to all three factors. Statistical analysis of data transformed to probits indicated mainly additive effects when factors were combined. Selective surgical treatments showed that the structural integrity of the pericarp was also important in germination control. Removal of the palea and lemma followed by the making of a shallow incision in the pericarp close to the embryo, stimulated germination in a very high proportion of individuals (94 %) even at a constant temperature (16°C) in the dark. Elevated oxygen levels promoted germination of intact seeds suggesting that the outer coverings might restrict oxygen access. Evidence is presented that positive pressures (0.03 MPa) applied during gassing led to a reduction in germination.

Oxygen toxicity in Streptococcus mutans: manganese, iron, and superoxide dismutase.

When cultured anaerobically in a chemically defined medium that was treated with Chelex-100 to lower its trace metal content, Streptococcus mutans OMZ176 had no apparent requirement for manganese or iron. Manganese or iron was necessary for aerobic cultivation in deep static cultures. During continuous aerobic cultivation in a stirred chemostat, iron did not support the growth rate achieved with manganese. Since the dissolved oxygen level in the chemostat cultures was higher than the final level in the static cultures, manganese may be required for growth at elevated oxygen levels. In medium supplemented with manganese, cells grown anaerobically contained a low level of superoxide dismutase (SOD) activity; aerobic cultivation increased SOD activity at least threefold. In iron-supplemented medium, cells grown anaerobically also had low SOD activity; aerobic incubation resulted in little increase in SOD activity. Polyacrylamide gel electrophoresis of the cell extracts revealed a major band and a minor band of SOD activity in the cells grown with manganese; however, cells grown with iron contained a single band of SOD activity with an Rf value similar to that of the major band found in cells grown with manganese. None of the SOD activity bands were abolished by the inclusion of 2 mM hydrogen peroxide in the SOD activity strain. S. mutans may not produce a separate iron-containing SOD but may insert either iron or manganese into an apo-SOD protein. Alternatively, iron may function in another activity (not SOD) that augments the defense against oxygen toxicity at low SOD levels.

The mechanism of toxic action of hyperbaric oxygenation on the mitochondria of rat-heart cells

Hyperbaric oxygenation of the whole animal was examined with respect to changes in mitochondria from heart cells. Accumulation of conjugated dienes, decrease of unsaturated fatty acids and changes in phospholipid pattern of the mitochondrial membrane indicate peroxidative damage of membrane lipids during oxygen stress. Hyperoxia induces increased activities of Superoxide dismutase, catalase and glutathione peroxidases, all enzymes protecting mitochondria from deleterious effects of reactive oxygen species. From the multiplicity of parameters related to pathophysiological effects of O 2 we inferred on increased formation rates of toxic oxygen species involving superoxide as the initial step in biological activation of O 2. The K m for superoxide formation was 550 μM, ranging above physiological oxygen levels by a factor of 11. Thus, the mechanism by which hyperoxia might affect stimulation of superoxide formation is discussed on the basis of enhanced Michaelis-Menten kinetics due to elevated oxygen levels in the heart tissue. The onset of the membrane damage is the first event in hyperbaric O 2 toxicity. Despite a clear induction, activities of protecting enzymes seem to be ‘swamped’ by raising oxygen concentration above normal.

Effect of oxygen- and carbon dioxide-enriched atmospheres on shelf-life extension of refrigerated ground pork

The oxidation of the lipids and myoglobin of ground pork meat stored in oxygen- and carbon dioxide-enriched atmospheres at 1 °C has been studied. Elevated oxygen levels (80–100%) depressed myoglobin oxidation, increasing the time to 50% metmyoglobin formation from four to about thirteen days. Twenty per cent carbon dioxide greatly reduced the rate of lipid oxidation, extending the time to reach a TBA number of 5 from five to about twelve days. Tocopherol and ascorbic acids were efficient inhibitors of lipid oxidation but citric acid was not.