Ascorbic acid and glutathione as respiratory carriers in the respiration of pea seedlings

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Abstract
With extracts prepared from germinat-ing pea seeds., reduced glutathione and ascorbic acid act as respiratory carriers in an enzyme system which transfers hydrogen to molecular O2 from substrates of TPN-linked dehy-drogenases. Enzymes in this respiratory pathway include dehydrogenase enzymes, glutathione reductase, dehydroascorbic acid reductase and ascorbic acid oxidase. Dehydroascorbic acid reductase was confined to the soluble part of the cytoplasm and was absent from the mitochondria. The O2 consumption of suspensions prepared from the cotyledons was of the same order of magnitude as that of the intact tissue, but O2 consumption of suspensions from the detached embryo was only about one-tenth that of the intact tissue. O2 consumption of suspen-sions from the cotyledons was almost equally distributed between the mitochondria and soluble fraction of the cytoplasm, but with suspensions from detached embryos the proportion of the respiration attributable to the soluble fraction decreased from 70% at 5 days to 50% after 9 days. Both cyanide and diethyldithiocarbamate, which in millimolar concentrations completely inhibited oxidation of ascorbic acid, equally depressed respiration of the soluble fraction from whole seedlings. Approximately 70% of the total O 2 consumption of the soluble fraction from cotyledons was cyanide-sensitive and, from the rate of reduction of dehydroascorbic acid by this fraction, it would appear possible that 60% of the cyanide-sensitive respiration might pass over the reduced glutathione-ascorbic acid system. This in turn suggests that 25% of the total respiration of the cotyledons may pass over this route. The reduced glutathione-ascorbic acid system may also function as a respiratory system in the detached embryo but, owing to the lack of correspondence between respiration of suspensions and intact tissue, no quantitative estimate of its importance can be given.

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