Changing respiratory pathways in potato tuber slices

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Abstract
The respiration of 1 mm thick slices of potato (Solanum tuberosum) tuber, initially slow and resistant to malonate inhibition, increases about 4-fold and becomes largely malonate sensitive during 24-36 hours of aging by aqueous incubation. The ability of the tissue to evolve C14O2 from exogenously supplied glucose-C14 increases several thousand fold during such aging. The nature of the initial respiration and changes during aging were studied by means of randomly and specifically labeled glucose-C14 fed during 1 to 3 hour incubation periods in the presence and absence of malonate. Respiratory C14O2 was collected and C1/C6 ratios were determined for each 10 minute interval. Distribution of label in alcoholic extracts was examined after fractionation by ion-exchange, paper electro-phoresis, and paper chromatography. The data are interpreted as indicating that the initial respiration is largely mediated by a system able to discriminate between C1 and C6 of glucose, presumably the pentose phosphate cycle. The tricarboxylic acid cycle, initially inactive, begins to function during the 1st 3 hours. Both systems are active in aged tissue. The major event occurring during physiological aging of slices is probably activation of the tricarboxylic acid cycle.