Studies in the respiratory and carbohydrate metabolism of plant tissues - IX. Experimental studies of the influence of oxygen at high pressures on the respiration of apples and of a 'block' in the tricarboxylic acid cycle induced by 'oxygen poisoning'

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Abstract
In contrast with peas (Turner and Quartley 1956; Pritchard 1959) apples treated with O2 at pressures of 2 1/2 or 5 atmospheres showed complex changes with time in the rate of CO2 output. These changes appeared to be due to the opposed effects of inhibitory and stimulatory processes; the latter caused a large increase in the rate of respiration in O2 as compared with that of samples held in air. Although then the observed rate of CO2 output after several days in O2 was, in general, only a little slower than the rate in air, taking into account the increased rate of respiration in O2, there was in fact a marked inhibition of a part or parts of the respiratory process. There was also an accumulation in O2 of pyruvate, alcohol and citrate and a decrease in the contents of [alpha]-ketoglutarate and oxaloacetate, as compared with apples in air. As in the earlier work with potatoes and peas (Barker and Mapson 1955; Turner and Quartley 1956), these changes in the acids were attributed in part to the production of an enzymic "block" in the tricarboxylic acid cycle between citrate and [alpha]-ketoglutarate. The indication in previous work (Allentoff, Phillips and Johnston 1954) that the tricarboxylic acid cycle may operate in apples was thus supported. The paper includes data on the influence of a return to air at a pressure of 1 atmosphere following subjection to O2 at high pressures.