Abstract
The respiration of potato tubers at 15[degree] C. increases when they are exposed to atmospheres containing low concentrations of HCN. The respiration rate goes through a typical 2-phase course: (1) a rise to a maximum, (2) a slower fall. During moderate cyanide treatment the respiratory quotient remains unchanged and the effects are reversible. During severe treatment, the onset of the falling phase is marked by an increased respiratory quotient, and irreversible in- jury occurs. During the rising phase the sugar content increases. In moderate cyanide the falling phase is accompanied by a parallel fall in sugar content, and there is no evidence of inactivation of respiratory enzymes. The changes in respiration rate in moderate cyanide treatment are due to changes in the concentration of sugar, which are interpreted as a direct effect of cyanide upon the starch-hydrolysing system of the potato, since analogous effects of cyanide have been observed with certain amylase extracts in vitro. During the falling phase in high cyanide, in addition to the development of an increased respiratory quotient, inactivation of the respiratory enzymes is shown by the decreased respiratory efficiency (the ratio respiration rate/ sugar concentration).

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