Effect of (+)-pulegone and other oil components of Menthaxpiperita on cucumber respiration

Peppermint (Mentha x piperita L.) essential oil and main components were as sessed for their ability to interfere with plant respiratory functions. Tes ts were conducted on both root segments and mitochondria isolated by etiola ted seedlings of cucumber (Cucumis sativus L.). Total essential oil inhibit ed 50% of root and mitochondrial respiration (IC50) when used at 324 and 59 3 ppm, respectively. (+)-Pulegone was the most toxic compound, with a 0.08 and 0.12 mM IC50 for root and mitochondrial respiration, respectively. (-)- Menthone, followed (+)-pulegone in its inhibitory action (IC50 values of 1. 11 and 2.30 mM for root and mitochondrial respiration respectively), wherea s (-)-menthol was the less inhibitory compound (IC50 values of 1.85 and 3.8 0 mM respectively). A positive correlation was found for (+)-pulegone, (-)- menthone and (-)-menthol between water solubility and respiratory inhibitio n. The uncoupling agent, carbonyl-cyanide-m-chlorophenyl-hydrazone (CCCP), lowered (-)-menthol and (-)menthone inhibition and annulled (+)-pulegone in hibition of mitochondrial respiration, whereas salicyl-hydroxamic acid (SHA M) 2-hydroxybenzohydroxamic acid, the alternative oxidase (AO) inhibitor, i ncreased (-)-menthone inhibition and annulled both (+)-pulegone and (-)-men thol inhibitory activity. The possible interaction of (+)-pulegone and (-)- menthol with AO and the mechanism of action of ( +)-pulegone, (-)-menthone and (-)-menthol on mitochondrial respiration are discussed. (C) 2001 Elsevi er Science Ltd. All rights reserved.