Evidence for a dual role for oxygen in control of abscission

Marynick, Marilyn C.; Addicott, Fredrick T.

doi:10.1038/264668a0

Cited by 6 publications

(1 citation statement)

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“…ferredoxinred + 02-+ 2H + -» H202 + ferredoxinox (2) In vivo, most electrons from reduced ferredoxin are passed onto nicotinamide adenine dinucleotide phosphate cation (NADP + ), via ferredoxin-NADP + reductase, to generate the NADPH needed to drive carbon dioxide fixation by the Calvin cycle. Thus electrons from photosystem I can pass through at least three routes (Figure 1), of which route C is preferred (11).…”

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confidence: 99%

Ascorbic Acid and the Illuminated Chloroplast

Halliwell

1982

Ascorbic Acid: Chemistry, Metabolism, and Uses

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The chloroplasts in the leaves of higher plants produce several damaging oxygen-derived species in the light, namely, hydrogen peroxide, singlet oxygen, lipid peroxides, superoxide, and the hydroxyl radical. The high concentra tion of ascorbic acid often present in the chloroplast helps to protect them against these species. Toxic Effects of Oxygen on Illuminated CbloroplastsOxygen is, by definition, essential for the life of all aerobic organisms, including higher plants, but oxygen has long been known to be toxic to aerobic organisms at concentrations greater than those in normal air. High oxygen concentrations inhibit chloroplast development, decrease seed viability and root growth, damage the membranes of leaves and roots, stimulate leaf abscission, and increase the incidence of growth abnormalities ( 1-3 ). Exposure to oxygen at a pressure of 6 atm is lethal to a wide variety of plants (4).Oxygen toxicity is seen not only in whole plants but also in cell cultures and even in isolated organelles. For example, high oxygen con centrations inhibit carbon dioxide fixation by isolated, intact chloroplast fractions (the so-called "Warburg effect"). Chloroplasts are especially prone to oxygen-toxicity effects because their internal oxygen concen tration during photosynthesis is probably somewhat greater than that in the air surrounding the leaf (5). The effects of elevated oxygen concen trations on chloroplasts are attributable to a number of factors (6), two of which are considered in the next sections.Generation of Superoxide Radicals and Hydrogen Peroxide in Chloroplasts. Isolated, illuminated chloroplast thylakoids slowly take up oxygen in the absence of added electron acceptors. This phenomenon was first observed by Mehler (7) and is often known as the "Mehler reaction." The reaction appears to result from the reduction of O 2 to the 0065-2393/82/0200-0263$06.00/0

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