INDUCTION AND ACTIVATION OF THE ALTERNATIVE OXIDASE OF POTATO-TUBER MITOCHONDRIA

Potato tubers (Solanum tuberosum L. cv. Grata) were stored for at least 1 week at room temperature and then incubated with an equal amount of apples (Malus domestica L.) for 2 days. After this treatment, intact tuber mitochondria isolated by Percoll gradient centrifugation showed a high degree of induction of the alternative oxidase, measured as cyanide-resistant, salicylhydroxamic acid-sensitive respiration. With succinate as substrate an activity of more than 130 nmol O2 (mg protein)-1 min-1 was obtained. An assay of the alternative oxidase using duroquinol as an electron donor was developed. To become reliable the assay required the presence of defatted bovine serum albumin (BSA) and catalase (EC 1.11.1.6). Furthermore, a lowering of the assay temperature to 15-degrees-C improved the stability of the duroquinol-based activity. One remarkable finding was that with duroquinol (or external NADH) as substrate the alternative oxidase was synergistically activated by succinate (as well as by malate) even in the presence of the succinate dehydrogenase inhibitor malonate. Our interpretation is that succinate and malate (indirectly) activate the alternative oxidase and that this activation is part of a physiological mechanism for regulation of the alternative oxidase.