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Articles

Cytokinin Modification of Mitochondrial Function ¹

Department of Biology, Indiana University, Bloomington, Indiana 47405

6-Benzylaminopurine, 6-(²-isopentenylamino)purine, 6-furfurylaminopurine, rotenone, and antimycin A inhibited oxidation of NADH by mitochondrial sonicates or submitochondrial particles (but not by intact mitochondria) from pea (Pisum sativum L., cult. Alaska) stems and mung bean (Vigna radiata L. Wilczak) hypocotyls. The above purine cytokinins can interfere with electron transport from NADH to the cytochrome system in the inner mitochondrial membrane. Adenine did not inhibit oxidation by sonicated mitochondria, and zeatin was almost ineffective. Zeatin scarcely inhibited state 3 malate respiration by intact mitochondria, but the O-formyl and O-n-propionyl esters of zeatin and the O-acetyl ester of 2-chlorozeatin were more active. Perhaps zeatin is ineffective because it does not get into the inner membranes of the isolated mitochondria, whereas the esters and other cytokinins mentioned above do. N-4-(2-chloropyridyl)-N'-Phenylurea, which has cytokinin-like effects on plant growth and development, inhibited NADH oxidation by sonicated mitochondria. It also inhibited malate, succinate, and NADH oxidation by intact mitochondria; in contrast, the latter two oxidations were not decreased by purine cytokinins.

The benzyl, isopentenyl, and furfuryl aminopurines inhibited malate (but not succinate) oxidation by rat liver mitochondria, if ADP was present. In the absence of ADP, these cytokinins promoted succinate (but not malate) oxidation. Zeatin and adenine had slight, if any, effect in either situation.