Studies in the respiratory and carbohydrate metabolism of plant tissues VI. Analysis of the interrelationships between the rate carbon dioxide production and the changes in the conten of lactic acid, sucrose and of certain fractions of keto-acid in potato tubers in air following anaerobic conditions

Abstract

In the previous paper (Barker & Mapson 1953) the loss of lactic acid which occurs in potato tubers in air after nitrogen and the accompanying increase followed by a decrease in the CO₂ output were shown to be associated with a rapid initial increase in the contents of ‘pyruvic’ and ‘α-ketoglutaric acids’ followed by a prolonged decrease in these fractions, From an analysis of these data in the present paper the time relations and magnitudes of the changes appear to be such that the increased output of CO₂ and the increased content of ‘pyruvic’ and ‘α-ketoglutaric acids’ during the initial phase in air after nitrogen can be ascribed to the oxidation of lactic acid to pyruvic acid and the respiration of the pyruvic acid, so produced, via the Krebs tricarboxylic cycle (Krebs & Johnson 1937 ; Krebs 1952). The analysis also indicates that the bulk of the initial outburst in CO₂ was produced by decarboxylation of ‘pyruvic acid’ with smaller contributions from ‘α-ketoglutaric acid’ and possibly from oxalosuccinic acid. The data are in accord with, but do not prove, the operation of the Krebs cycle in potato I tubers. Reference is made to the earlier observations of Miller, Guthrie & Denny (1936) that potatoes treated with various volatile compounds showed an outburst of CO₂ accompanied by a loss of citric acid. The present authors suggest that this loss of citric acid may be associated with a temporary increase in the content and/or the rate of decarboxylation of ‘α-ketoglutaric acid’. If further work substantiates this hypothesis, there will be strong evidence for the occurrence of the Krebs cycle in potatoes.