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Effect of Adenine Nucleotides on the Respiration of Carrot Root Slices

^a Botany School, University of Melbourne, Parkville, Victoria, 3052, Australia

Sodium pyruvate and dinitrophenol stimulated O₂ uptake of freshly cut phloem parenchyma from carrot roots by 63 and 120% at optimal concentrations, indicating that production of pyruvate by glycolysis regulates over-all respiratory rate. Adding 0.5 to 6.7 mM Na₃ADP and Na₃ATP to slices rapidly stimulates respiration rate by 20 to 85%. The effect is greater at the lower end of this concentration range and is not due to change in pH or active cation uptake. It is suggested that treating tissue with both nucleotides stimulates pyruvate kinase, the rate-limiting step in respiration of freshly cut slices, by increasing the concentration of endogenous ADP. Adenosine diphosphate continued to stimulate O₂ uptake until the peak of induced respiration, but ATP inhibited respiration during development and decline of this peak. Absence of respiratory stimulation by NaH₂PO₄ and of respiratory inhibition by added nucleosides confirms that inorganic phosphate is not a limiting factor of respiration in freshly cut slices. The stimulation of respiration rate of these slices by dinitrophenol is consistent with results from experiments in which ADP and ATP were applied to the tissue.