Carbon Dioxide Fixation and Ion Absorption in Barley Roots.

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Abstract
C14O2 fixation in young excised barley roots was influenced to a considerable degree by the type of concurrent ion absorption. During excess cation absorption, the C14O2 fixed was more than double that occurring in distilled water or during equivalent cation and anion absorption, and six times greater than the amount fixed during excess anion absorption. When excess cation absorption took place, 92% of the fixed C14 was found in the malate. During excess anion absorption, 41% of the fixed C14 was in the malate. Although malate and C14O2 fixation increased considerably during excess cation absorption, no quantitative relationship was found between the two processes. Pyrrolidone carboxylic acid, derived from glutamine by the extraction process, was the next most strongly labeled acid, although much less than malate. Other organic acids were weakly labeled. The malate was preferentially and about equally labeled in the [alpha] and [beta] carboxyl positions. Only the carboxyl group in the pyrrolidone carboxylic acid was labeled. It is suggested that CO2 fixation plays an important role in the synthesis of malate in young barley plants.