Active Oxygen Metabolism Research Articles

An activated-oxygen-mediated role for peroxisomes in the mechanism of senescence of Pisum sativum L. leaves

The possible involvement of peroxisomes and their activated-oxygen metabolism in the mechanism of leaf senescence was investigated in detached pea (Pisum sativum L.) leaves which were induced to senesce by incubation in complete darkness for up to 11 d. At days 0, 3, 8, and 11 of senescence, peroxisomes were purified from leaves and the activities of different peroxisomal and glyoxysomal enzymes were measured. Xanthine-oxidoreductase activity increased with senescence, especially the O2. --producing xanthine oxidase (EC 1.1.3.22). The activities of H2O2-generating Mn-superoxide dismutase (EC 1.15.1.1) and urate oxidase (EC 1.7.3.3) were also enhanced by senescence, whereas catalase (EC 1.11.1.6) activity was severely depressed. Hydrogen peroxide concentrations increased significantly in senescent leaf peroxisomes. During the progress of senescence, glycollate oxidase (EC 1.1.3.1) and hydroxypyruvate reductase (EC 1.1.1.81), two marker enzymes of photorespiratory metabolism, gradually decreased in activity and disappeared. At the same time, the activities of malate synthase (EC 4.1.3.2) and isocitrate lyase (EC 4.1.3.1), key enzymes of the glyoxylate cycle, which were undetectable in presenescent leaves, increased dramatically upon induction of senescence. Ultrastructural studies of intact leaves showed that the population of peroxisomes and mitochondria increased with senescence. Results indicate that peroxisomes could play a role, mediated by activated oxygen species, in the oxidative mechanism of leaf senescence, and further support the idea, proposed by other authors, that foliar senescence is associated with the transition of leaf peroxisomes into glyoxysomes.

Effect of flooding on the activities of some enzymes of activated oxygen metabolism, the levels of antioxidants, and lipid peroxidation in senescing tobacco leaves

Effects of flooding on the activities of some enzymes of activated oxygen metabolism, the levels of antioxidants, and lipid peroxidation in senescing leaves of tobacco were investigated. As judged by the decrease in chlorophyll and protein levels, flooding accelerated the senescence of tobacco leaves. Total peroxide and the lipid peroxidation product, malondialdehyde, increased in both control and flooding-treated leaves with increasing duration of the experiment. Throughout the duration of the experiment, flooded leaves had higher levels of total peroxide and malondialdehyde than did control leaves. Flooding resulted in an increase in peroxidase and ascorbate peroxidase activities and a reduction of superoxide dismutase activity in the senescing leaves. Glycolate oxidase, catalase, and glutathione reductase activities were not affected by flooding. Flooding increased the levels of total ascorbate and dehydroascorbate. Total glutathione, reduced form glutathione, or oxidized glutathione levels in flooded leaves were lower than in control leaves during the first two days of the experiment, but were higher than in control leaves at the later stage of the experiment. Our work suggests that senescence of tobacco induced by flooding may be a consequence of lipid peroxidation possibly controlled by superoxide dismutase activity. Our results also suggest that increased rates of hydrogen peroxide in leaves of flooded plants could lead to increased capacities of the scavenging system of hydrogen peroxide.

Salt‐induced oxidative stress mediated by activated oxygen species in pea leaf mitochondria

The effect in vivo of salt stress on the activated oxygen metabolism of mitochondria, was studied in leaves from two NaCl‐treated cultivars of Pisum sativum L. with different sensitivity to NaCl. In mitochondria from NaCl‐sensitive plants, salinity brought about a significant decrease of Mn‐SOD (EC 1. 15. 1. 1) Cu, Zn‐SOD I (EC 1. 15. 1. 1) and fumarase (EC 4. 2. 1. 2) activities. Conversely, in salt‐tolerant plants NaCl treatment produced an increase in the mitochondrial Mn‐SOD activity and, to a lesser extent, in fumarase activity. In mitochondria from both salt‐treated cultivars, the internal H2O2 concentration remained unchanged. The NADH‐ and succinate‐dependent generation of O2.−radicals by submitochondrial particles and the lipid peroxidation of mitochondrial membranes, increased as a result of salt treatment, and these changes were higher in NaCl‐sensitive than in NaCl‐tolerant plants. Accordingly, the enhanced rates of superoxide production by mitochondria from salt‐sensitive plants were concomitant with a strong decrease in the mitochondrial Mn‐SOD activity, whereas NaCl‐tolerant plants appear to have a protection mechanism against salt‐induced increased O2.− production by means of the induction of the mitochondrial Mn‐SOD activity. These results indicate that in the subcellular toxicity of NaCl in pea plants, at the level of mitochondria, an oxidative stress mechanism mediated by superoxide radicals is involved, and also imply a function for mitochondrial Mn‐SOD in the molecular mechanisms of plant tolerance to NaCl.

活性酸素代謝の分子的機作の解明

活性酸素代謝の分子的機作の解明

Influence of Age and Caloric Restriction on Expression of Hepatic Genes for Xenobiotic and Oxygen Metabolizing Enzymes in the Mouse

The influence of age and life-span-prolonging caloric restriction on the expression of hepatic genes for xenobiotic and activated oxygen metabolism was investigated in female C3B10RF1 mice, a long-lived hybrid strain. Animals were fed either ad libitum, or diets reduced 20% or 52% in total calories but approximately unchanged in total protein, vitamins, and minerals. Cytochrome P1- and P3-450 (cyp1A1 and cyp1A2, respectively) mRNA levels decreased approximately 40% between age 4-5 months (young) and 30-31 months (old) in ad libitum fed animals (p less than or equal to .05). Caloric restriction eliminated this decrease. Manganese-superoxide dismutase mRNA decreased significantly in old ad libitum fed mice, and caloric restriction eliminated this decrease. No change in manganese-superoxide dismutase activity was detected, probably due to its low level and the large variability inherent in the assay. Catalase mRNA increased with age, but was not affected by diet. Catalase activity increased significantly with caloric restriction in young and old mice, in the absence of an increase in catalase mRNA, suggesting translational or posttranslational effects. CuZn-superoxide dismutase, glutathione peroxidase and epoxide hydrolase mRNA, and the ratio of ribosomal to total mRNA did not change with age or diet.

Timing of molecular events following elicitor treatment of plant cells

Extracellular products with elicitor activity from the bean pathogen Colletotrichum lindemuthianum induced a multiplicity of changes in bean suspension cells. An immediate increase in luminol-mediated chemiluminescence which peaked within 30 min indicated production of activated oxygen species. Shut down of synthesis of discrete proteins and enhanced synthesis of other proteins was apparent by 3 h. These differences in protein profiles between elicitor-treated and control cells were more pronounced by 6 h. Other changes at 4–6 h involved perturbations in membrane functions including lipid peroxidation, altered proton efflux and uptake of a vital stain, fluorescein diacetate as well as reduced activity of the extracellular enzymes peroxidase and β glucosidase. These changes coincide with an increase in electron paramagnetic resonance signal consistent with free radical accumulation. The accumulation of phytoalexins at 6–8 h after treatment suggests that phytoalexins do not account for either free radicals detected earlier by the electron paramagnetic resonance signals or altered plant membrane function. Our data suggest that altered protein expression may be triggered by free radicals connected to activated oxygen metabolism.

A new cellular function for peroxisomes related to oxygen free radicals?

Although in cell biology peroxisomes are still 'young' organelles, it is becoming increasingly clear that they are involved in important cellular functions. Recent results have indicated the presence of the metalloenzyme superoxide dismutase in peroxisomes and the production of superoxide free radicals (O2-) in these oxidative organelles. These findings, together with other experimental evidence, point towards the existence of new roles for peroxisomes in cellular active oxygen metabolism, something that has a potential impact in multiple areas of cell biology, particularly in biochemistry and biomedicine.

Effect of Paclobutrazol on the Activities of some Enzymes of Activated Oxygen Metabolism and Lipid Peroxidation in Senescing Soybean Leaves

Summary Nineteen-day-old soybean [Glycine max (L.) Merr. cv. A 2] plants were treated with soil-applied paclobutrazol, an antigibberellin growth inhibitor, at the rate of 125 µg per 10 cm pot. The plants were then grown for 14 days under a 14 hr photoperiod after which they were transferred to the dark for senescence induction. At the end of the 14 day period in the light, treated plants exhibited higher chlorophyll (Chl) content and higher activities of catalase and glycolate oxidase compared to controls. In contrast, control leaves had higher activities of superoxide dismutase and a higher content of malondialdehyde (MDA), a product of lipid peroxidation. Upon transfer to dark, Chl and protein content declined in both control and treated plants, but the decline was much faster in controls. The activity of catalase declined markedly in controls while remaining constant in reated plants. Peroxidase and superoxide dismutase activities and MDA content increased in controls in the dark but remained relatively constant in treated plants. These results suggest that paclobutrazol delays dark-induced senescence in attached soybean leaves and that this delay is associated with the maintenance of catalase activity and the prevention of the senescence-linked rise in peroxidase activity and lipid peroxidation.