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Regulation of Salt Respiration in Carrot Root Slices

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

In slices of carrot-phloem parenchyma washed for 7 days in water at 20 C, 50 mM KCl stimulates respiration by up to 100% of the ground respiration within 4 minutes of application. The data presented imply that ADP liberated in the cytoplasm as a consequence of KCl accumulation first stimulates a regulator reaction requiring ADP (phosphoglycerate kinase). Thereafter, the point of control alternates between this reaction and the phosphofructokinase reaction, forming a sequence of enzyme stimulations which continue after the new steady state of increased respiration is established. KCl induces a similar sequence in slices washed for 3 days, but it is completed within 3 minutes, and metabolite oscillations are not so marked. In slices washed for 2 days, KCl stimulates respiration by less than 10%, and the sequence of regulator reactions does not occur. Phosphoglycerate kinase is the only enzyme stimulated within 3 minutes of applying KCl to these slices. Contrary to previous reports, KCl frequently stimulates the respiration of freshly prepared slices by 10 to 30%.

² Present address: The Walter and Eliza Hall Institute of Medical Research, Post Office, Royal Melbourne Hospital, Parkville, Victoria 3052, Australia.