The mechanism of changes in respiratory activity during callus formation in carrot root slices cultured in vitro

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The rates of both O_2 uptake in air and CO_2 output in N_2 per protein nitrogen and per cell increased markedly during the lag phase of callus formation, and decreased rapidly then gradually, during the exponential and subsequent phases in carrot-root phloem slices cultured in vitro. Rates of ^<14>CO_2 output from labeled citrate and succinate supplied to the slices changed similarly. Respiration of the cultured slices became more sensitive to fluoride and cyanide during the lag phase and less sensitive during the exponential phase. These results suggest that activities of both the glycolytic pathway and the TCA cycle rise during the lag phase and decline during the exponential one. The activities per protein nitrogen of the glycolytic enzymes, hexokinase, phosphoglucose isomerase, phosphofructokinase, aldolase and pyruvate kinase remarkably increased during the lag phase after a little decline in the first day of culture, and decreased as the callus developed. A similar pattern of change was observed in the number and the respiratory activity of mitochondria per cell. It was concluded, therefore, that changes in respiratory activity during callus formation may depend mainly on changes in capacity of the respiratory machinery, although the increase in respiratory activity at the beginning of culture may be due to some other mechanism, such as an increase in the turnover rate of ATP.
日本植物生理学会の論文