| 1. |
- KROMER, S, et al.
(författare)
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MITOCHONDRIAL CONTRIBUTION TO PHOTOSYNTHETIC METABOLISM - A STUDY WITH BARLEY (HORDEUM-VULGARE L) LEAF PROTOPLASTS AT DIFFERENT LIGHT INTENSITIES AND CO2 CONCENTRATIONS
- 1993
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Ingår i: Plant Physiology. - 0032-0889 .- 1532-2548. ; 102:3, s. 947-955
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Tidskriftsartikel (refereegranskat)abstract
- An oligomycin concentration that specifically inhibits oxidative Phosphorylation was added to isolated barley (Hordeum vulgare L.) leaf protoplasts at various irradiances and carbon dioxide concentrations. At saturating as well as low light intensities, photosynthetic oxygen evolution was decreased as a result of the oligomycin treatment, whereas no effect was observed at intermediate light intensities. This was the same for photorespiratory and nonphotorespiratory conditions. These results were confirmed by measurements of fluorescence quenching under the same conditions. Metabolite analysis in the presence of oligomycin revealed a drastic decrease in the mitochondrial and cytosolic ATP/ADP ratios, whereas there was little or no effect on the chloroplastic ratio. Concomitantly, sucrose phosphate synthase activity was reduced. Under high irradiances, this inhibition of sucrose synthesis by oligomycin apparently caused a feedback inhibition on the Calvin cycle and the photosynthetic activity. Under low irradiances, a feedback regulation compensated, indicating that light was more limiting than the activity of regulative enzymes. Thus, the importance of mitochondrial respiratory activity might be different in different metabolic situations. At saturating light, the oxidation of excess photosynthetic redox equivalents is required to sustain a high rate of photosynthesis. At low light, the supply of ATP to the cytosol might be required to support biosynthetic reactions.
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| 2. |
- WIGGE, B, et al.
(författare)
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THE REDOX LEVELS AND SUBCELLULAR-DISTRIBUTION OF PYRIDINE-NUCLEOTIDES IN ILLUMINATED BARLEY LEAF PROTOPLASTS STUDIED BY RAPID FRACTIONATION
- 1993
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Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 88:1, s. 10-18
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Tidskriftsartikel (refereegranskat)abstract
- The redox level and compartmentation of pyridine nucleotides was studied under photorespiratory and non-photorespiratory conditions using rapid fractionation of barley (Hordeum vulgare L. cv. Gunilla, Svalov) leaf protoplasts. From comparative measurements of the NADPH/NADP+ ratio and the ATP/ADP ratio one acidic and one alkaline extraction medium was chosen which quenched the metabolism very efficiently. The mitochondrial NADH/NAD+ was higher under photorespiratory conditions than under non-photorespiratory conditions. Aminoacetonitrile, an inhibitor of the photorespiratory conversion of glycine to serine, lowered the mitochondrial NADH/NAD+ ratio. This supports the hypothesis that glycine oxidation is coupled to oxidative phosphorylation to provide ATP to the cytosol. The chloroplastic NADPH/NADP+ as well as the NADH/NAD+ ratios were quite stable in saturating and limiting CO2 as well as in the presence of aminoacetonitrile, although the triosephosphate/phosphoglycerate ratios changed. Thus, the redox level in the stroma seems to be tightly regulated.
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