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

Abstract

The respiratory changes which take place in slices of tubers and tuberous roots have long been of interest to plant physiologists. As early as 1887, the wound respiration of white potato tubers was described (3), and since then many of the factors affecting this phenomenon have been analyzed (17). In recent years, the fact that the developed respiration is resistant to cyanide and carbon monoxide has attracted special attention (18, 25). Since the respiration of freshly cut slices can be shown to be mediated by cytochrome oxidase, it has been concluded that there must be some fundamental modification of the respiratory chain during the ageing of these slices. That the cytochrome system does function in aged slices is suggested by the demonstration that their ability to absorb water is inhibited by CO and this effect is reversed by light (15). In addition, the respiratory system shows a high affinity for oxygen (25). These facts pose a number of important questions: a) What electron transport pathway is functional in aged potato slices and in other plant tissues which have a cyanideand CO-resistant respiration? b) How can CO block an energy-requiring process without reducing the net rate of electron transfer ? c) What type of transformation underlies the quantitative and qualitative changes in tissue respiration? The potato tuber slices, in which there is a striking change within one day, seem ideally suited for further investigations on the problem of inhibitorresistant respiration. The plan of the present study has been to compare the respiratory mechanisms in freshly-cut and day-old slices, and to ascertain the conditions necessary for the development of the wound respiration. The work has been carried on at two levels: with tissue slices and with isolated cell fractions. Oxygen uptake has been used as a measure of respiratory activity, and its coupling to phosphorylation estimated by following phosphate uptake. The respiratory components involved in hydrogen and electron transport have been examined by both enzymatic and spectrophotometric techniques. The evidence indicates that during the aerobic incubation of potato slices there is a metabolism-dependent modification of the mitochondrial respiratory chain, probably within the cytochrome system. Preliminary reports on this work have already been published (8, 9, 10, 13).