THE REDOX LEVELS AND SUBCELLULAR-DISTRIBUTION OF PYRIDINE-NUCLEOTIDES IN ILLUMINATED BARLEY LEAF PROTOPLASTS STUDIED BY RAPID FRACTIONATION

• 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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