Studies on Development of Cyanide-resistant Respiration in Potato Tuber Slices

Abstract

During a 1-day in-cubation, thin slices of potato tuber tissue develop (1) a rapid respiration which is relatively resistant to CO, cyanide, azide, and antimycin, and (2) the capacity to accumulate p32 actively by an aerobic mechanism which is photo-reversibly inhibited by CO. These changes are dependent on the tissue''s metabolism and do not take place at low temperatures. The change in respiratory rate is not the result of a progressive uncoupling from phosphorylation. The kinetics of the change and the fact that it can be prevented by anaerobic conditions and by 2,4-dinitrophenol suggest that it is closely linked to synthetic activities. The rates of oxidation of Krebs cycle acids and the efficiencies of phosphorylation (P/O with [alpha]-ketoglutarate, 2-3) are similar. The oxidations by aged-tissue particles are less sensitive to cyanide, which is nevertheless able to uncouple phosphorylation. After 1 day, there is a several-fold increase in the DPNH oxidase, diaphorase, and DPNH-cytochrome c reductase activities, without a significant increase in cytochrome c oxidase and succiniccytochrome c reductase. The rapid DPNH oxidase remains sensitive to cyanide, azide, and antimycin. There is also a marked increase in the micro-somal DPNH-cytochrome c reductase. Spectrophotometric examinations of the DPNH-reduced respiratory chain show flavoprotein, cytochrome a, a3,b7, and c components in mitochondria from both types of tissue. The difference spectra reveal an apparent increase, after ageing, in the amount of b-type cytochrome relative to the a-a3 components. The results suggest that there is a modification of the chain in the region between DPNH and cytochrome c, and the possible relations of this to the tissue-level changes are discussed.