Cyanide-insensitive and Cyanide-sensitive O2 Uptake in Wheat

Abstract

The mitochondrial fraction isolated from durum wheat seedlings by differential centrifugation demonstrated antimycin A- or cyanide-insensitive O(2) uptake. Further purification of this initial mitochondrial pellet using a linear Percoll (Pharmacia) density gradient separated the mitochondria into two bands of physiologically distinct activity. Based on the usual mitochondrial respiratory criteria of ADP/O and respiratory control values, these fractions were qualitatively similar to the crude pellet. However, we observed no antimycin A-insensitive O(2) uptake in either gradient band. Antimycin A-insensitive O(2) consumption could be restored to the upper gradient band of mitochondria by the addition of linoleic acid. This activity was inhibited either by salicylhydroxamic acid or propyl gallate, a known lipoxygenase inhibitor. Likewise, addition of linoleic acid to the crude mitochondrial pellet elicited a 4- to 5-fold increase in O(2) uptake. This O(2) consumption was insensitive to antimycin A and cyanide but was inhibited by either propyl gallate or salicylhydroxamic acid. Electron microscopic examination revealed that only the lower gradient band contained contamination-free mitochondria, which, in turn, lacked ability to oxidize linoleic acid. Antimycin A-insensitive O(2) consumption in the differential centrifugation fraction from germinating durum wheat seedlings decreased over 64 hours of development.