Effects of rotenoids on isolated plant mitochondria

The effects of several rotenoids have been studied on potato (Solanum tuberosum L.) tuber and etiolated mung bean (Phaseolus aureus Roxb.) hypocotyls mitochondria. The selective inhibition of mitochondrial complex I is characterized by several tests: (a) no effect can be observed on exogenous NADH or succinate oxidation; (b) malate oxidation is inhibited at pH 7.5; (c) one-third decrease of ADP/O ratio appears during malate oxidation at pH 6.5 or during alpha-ketoglutarate, citrate, or pyruvate oxidation at a pH about 7; (d) during malate oxidation at pH 6.5, a transient inhibition appears which can be maintained by addition of exogenous oxaloacetate; (e) in potato mitochondria, the inhibition of malate oxidation disappears at pH 6.5 when NAD(+) is added. Then, a one-third decrease of the ADP/O ratio can be measured.Such a selective inhibition of complex I is obtained with deguelin, tephrosin, elliptone, OH-12 rotenone, and almost all the rotenoids extracted from Derris roots. The presence of the rings A, B, C, D, E seems to be necessary for the selective inhibition. Opening of the E ring and hydroxylation of the 9 position (rot-2'-enoic acid) give a rotenoid derivative with multisite inhibitory activities on flavoproteins, which are quite comparable to those of common flavonoids such as kaempferol (Ravanel et al. 1982 Plant Physiol 69: 375-378).