Superoxide formation in spinach chloroplasts: Electron spin resonance detection by spin trapping

Maize seedlings, treated with the herbicide norflurazon to produce a deficiency in carotenoid pigments, were grown in low-fluence-rate light. Under these conditions, which induced chlorophyll biosynthesis while minimizing photooxidation, carotenoid-deficient seedlings showed identical patterns of chloroplast protein accumulation compared with normal seedlings. Carotenoid pigments thus play no direct role in regulating the accumulation of chloroplast proteins. When shifted to high-fluence-rate light, chlorophyll was rapidly photooxidized in carotenoid-deficient seedlings. Chloroplast proteins showed varying degrees of sensitivity to photooxidation. The P-700 apoprotein of photosystem I was rapidly degraded. Most stromal and thylakoid proteins either decreased progressively in photooxidative conditions or appeared to be unaffected. The relative quantity of the light-harvesting chlorophyll a/b-binding protein of photosystem II increased significantly in the first few hours of highfluence-rate light. It then appeared to be only minimally affected 18 hours after complete photooxidation of chlorophyll.Nuclear mutations which completely block the accumulation ofcarotenoid pigments exhibit a wide range ofpleiotropic effects.

Section: Resultsmentioning

confidence: 99%

The Fate of Chloroplast Proteins during Photooxidation in Carotenoid-Deficient Maize Leaves

Mayfield¹,

Nelson²,

Taylor³

1986

“…Paraquat is known to form cation radicals which react with 02 to produce the superoxide radical 02 (6,8,22). Moreover, the presence of 02 accentuates the sensitivity of plants and animals to paraquat (22), and it seems that 02-generated by cyclic redox processes may well be the agent of paraquat toxicity.…”

Section: Methodsmentioning

confidence: 99%

“…Its phytotoxicity is dependent on formation of the highly reactive superoxide radical (02) that arises when the partially reduced dipyridal cation is reoxidized by molecular oxygen (6,22). Indeed, spin trapping techniques have revealed that the addition of 1 mm paraquat to illuminated chloroplast suspensions enhances the production of 02 by up to 10-fold (8). In the present study, we have examined the ability of paraquat to simulate the effects of senescence on membranes.…”

mentioning

confidence: 98%

Simulation of the Effects of Leaf Senescence on Membranes by Treatment with Paraquat

Chia¹,

Thompson²,

Dumbroff³

1981

Chloroplast and microsomal membranes from the primary leaf of bean acquired increasing proportions of gel phase lipid as the tissue senesced. The lipid-phase transition temperature for microsomes rose from about 25 to 43 C and that for chloroplasts rose from below -30 C to about 52 C within 5 weeks of planting. This was accompanied by large increases (2-to 4-fold) in the sterol to phospholipid ratio of the membranes, which reflected breakdown of phospholipid. Changes in fatty acid saturation were of insufficient magnitude to account for the rise in transition temperature. AU of these senescence-related changes in chloroplast and microsomal membranes were also induced by treating young, 2-week-old-plants with 10 milligrams per liter paraquat. Within 48 hours of treatment, the transition temperature rose from 25 to 57 C for microsomes and from below -30 to 24 C for chloroplasts. The membranes sustained only small changes in fatty acid saturation, comparable to those incurred during natural senescence, and there was a selective loss ofphospholipid, resulting in augmented sterol to phospholipid ratios. Malondialdehyde, a product of lipid peroxidation, rose by 2-to 3-fold in both senescing and paraquat-treated leaves. Paraquat is known to form cation radicals that react with 02 to produce 02 and has been implicated as an agent of lipid peroxidation. Accordingly, these observations suggest that membrane deterioration during natural senescence may be due in part to free radical damage.

“…The second reaction complex depends on the photosynthetic reduction of 02 to H202, well known as the Mehler reaction (7,8,(16)(17)(18)20), which has now been shown to proceed via the superoxide radical anion and might be at least partly mediated by an O2-reducing factor (7,8).…”

Section: Introductionmentioning

confidence: 99%

“…With osmotically broken chioroplsts this ratio was 1.2 at 30 FM 02 and almost 1 from 150 FM onward. When the 02 surplus found in broken chloroplasts during photosynthesis was related to the volume of the thylakoids, a ratio of about 2.3 was observed.At least three reaction complexes of chloroplasts are thought to depend on the internal 02 concentration in these organelles.First, the Warburg effect, an inhibition of photosynthesis by higher oxygen tensions, has given rise to a series of physiological studies that were dedicated to an understanding of the responsible biochemical mechanism (5,6,21,22).The second reaction complex depends on the photosynthetic reduction of 02 to H202, well known as the Mehler reaction (7,8,(16)(17)(18)20), which has now been shown to proceed via the superoxide radical anion and might be at least partly mediated by an O2-reducing factor (7,8).Third, 02 has been shown to react in the ribulose-1,5-diphosphate oxygenase reaction (1, 2). Although the internal 02 concentration of chloroplasts, which might depend on the photosynthetic 02 production as well as on the 02 tension outside the chloroplasts, is important for the metabolism of the cell, no reports are to be found in the literature on its magnitude.…”

mentioning

confidence: 99%

Oxygen Concentration in Isolated Chloroplasts during Photosynthesis

Steiger

Beck

1977

The 02 concentration in intact and osmoially disrupted isolated spinach (Spinacia oleracea, L.) chloroplasts during photosynthesis was estimated. The chloroplasts were allowed to reduce 3-phosphoglycerate, C02, or ferrcyanide in ltht until the rate of 02 production was linear.When the liht was turned off 02 evolution from the chloroplasts continued for a few seconds. This prolonged 02 evolution is due to an 02 surpus inside the chloroplas which equilibrates with that in the medium. From this surplus the 02 concentration inside the chloroplasts at the moment when the light had been switched off was caldculated. In all experiments the 02 concentration inside the photosyntheszing chloroplasts was higher than that outsde, but was dependent upon the 02 concentrtion of the chioroplast mediunm. At low exteral 02 concentration (30 pM) the ratio of the internal to the external 02 concentration was about 5, whereas at concentrations corresponding to those in airsaturated water this ratio was dose to 1. With osmotically broken chioroplsts this ratio was 1.2 at 30 FM 02 and almost 1 from 150 FM onward. When the 02 surplus found in broken chloroplasts during photosynthesis was related to the volume of the thylakoids, a ratio of about 2.3 was observed.At least three reaction complexes of chloroplasts are thought to depend on the internal 02 concentration in these organelles.First, the Warburg effect, an inhibition of photosynthesis by higher oxygen tensions, has given rise to a series of physiological studies that were dedicated to an understanding of the responsible biochemical mechanism (5,6,21,22).The second reaction complex depends on the photosynthetic reduction of 02 to H202, well known as the Mehler reaction (7,8,(16)(17)(18)20), which has now been shown to proceed via the superoxide radical anion and might be at least partly mediated by an O2-reducing factor (7,8).Third, 02 has been shown to react in the ribulose-1,5-diphosphate oxygenase reaction (1, 2). Although the internal 02 concentration of chloroplasts, which might depend on the photosynthetic 02 production as well as on the 02 tension outside the chloroplasts, is important for the metabolism of the cell, no reports are to be found in the literature on its magnitude.Here, we attempted to estimate the internal 02 concentration of photosynthesizing isolated chloroplasts and to determine how much this 02 content can be influenced by the 02 tension of the suspension medium of the chloroplasts.