‘Compartmentation’ of acids in plant tissues

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Abstract
The amounts of various Krebs-cycle acids and of glutamate and aspartate present in maize-root tissue of 3 different ages, maize coleoptiles, beet- and carrot-root tissue, and Bryophyllum and wheat leaves were determined. Features of [1-C14]acetate utilization by these tissues were examined. Cl4 from [1-Cl4]acetate was found equally and only in the carboxyl carbons of malate, it was confined to the carboxyl groups of citrate, and distributed in a 1:2 ratio between C-l and C-5 of glutamate. These results confirm that acetate was being utilized by the Krebs cycle. The progress of incorporation of C14 from [1-C14] acetate into adds, amino acids and carbon dioxide with time was determined, and changes in the specific activities of these components were measured. When the specific activity of the carbon dioxide reached a constant value, indicating that equilibrium had been reached in the turnover pools of the acids of the Krebs cycle, there were great differences in the observed specific activities of the adds. These differences are ascribed to the existence of pools of acids and amino acids not in ready equilibrium with the turnover pools, but which mixed with them during extractioa By correcting the specific activity of the carbon dioxide to allow for the production of carbon dioxide in reactions other than those of the Krebs cycle, and comparing this value with the specific activities of the carboxyl groups of the acids, the fraction of each add which was in equilibrium with the turnover pools was estimated. The results show that large amounts of individual adds are physically remote from the respiratory centers, and that the amounts of adds in turnover pools in the various tissues are different. The evidence from the maize-root tissues of different ages shows that, as vacuolation occurs, the relative amount of acids not in turnover pools (i.e. out of equilibrium with the carbon dioxide) increases markedly.