Effects of α-pinene on the mitochondrial respiration of maize seedlings

The effects of alpha-pinene, which is one of the major components of essential oils of several aromatic species, on energy metabolism of mitochondria isolated from maize (Zea mays L.) coleoptiles and primary roots were investigated. alpha-Pinene exerted similar effects on oxygen consumption irrespective of the source of mitochondria or of the substrate (L-malate, succinate or NADH). At concentrations lower than 250 muM, alpha-pinene stimulated respiration in state IV and inhibited respiration in state III. At higher concentrations the effect of alpha-pinene on state IV respiration was shifted toward inhibition. Complete suppression of respiratory control ratio was evident at alpha-pinene concentrations higher than 100 muM. When mitochondria were uncoupled with carbonyl cyanide 4-trifluoromethoxyphenyl-hydrazone (FCCP), alpha-pinene caused only inhibition of respiration. In the presence of alpha-pinene, the transmembrane potential was decreased as indicated by changes in the safranine binding by energized mitochondria. alpha-Pinene did not affect the activities of succinate dehydrogenase (EC 1.3.5.1) and L-malate dehydrogenase (L-malate:NAD(+) oxidoreductase; EC 1.1.1.37). The results indicate that alpha-pinene acts by at least two mechanisms: uncoupling of oxidative phosphorylation and inhibition of electron transfer. Confirming the impairment of mitochondrial energy metabolism, alpha-pinene strongly inhibited mitochondrial ATP production. It is apparent that the actions of alpha-pinene on isolated mitochondria are consequences of unspecific disturbances in the inner mitochondrial membrane. (C) 2003 Editions scientifiques et medicales Elsevier SAS. All rights reserved.