Abstract: Monoterpenes inhibit seed germination and plant growth in the chemical interaction among plants known as allelopathy. Peppermint (Mentha piperita L.) essential oil and some of its oil components affected root and mitochondrial respiration as well as membrane permeability and ion uptake of cucumber (Cucumis sativus L.). Total essential oil had an inhibitory action by inhibiting 50% of root and mitochondrial respiration (I50) when used at 324 and 593 ppm, respectively. Pulegone had an I50 on root and mitochondrial respiration at the concentration of 0.08 mM and 0.12 mM, respectively. Menthone followed pulegone in its inhibitory action with a root respiration I50 of 1.11 mM and mitochondrial I50 of 2.30 mM, whereas menthol was the less inhibitory compound, with root respiration I50 of 1.85 mM and mitochondrial I50 of 3.80 mM. A direct correlation between water solubility and respiratory inhibition was found for pulegone, menthone and menthol. The possible interaction of pulegone, menthone and menthol on mitochondrial respiration will be discussed. Cucumber root membrane potentials were depolarized up to Goldman’s potential after perfusion with 300 ppm menthone, 300 ppm menthol and 150 ppm of menthone + 150 ppm menthol. Pulegone, neomenthol and menthofuran were also found to strongly depolarize root membrane potentials, whereas no significant effects were measured after limonene, 1,8-cineole and menthyl acetate perfusion. Total essential oil perfusion was found to specifically block potassium uptake, as demonstrated with the use of the potassium inward channel-blocker cesium. Washing roots with a fresh buffered solution annulled total oil, menthol, pulegone, menthofuran and neomenthol depolarization, whereas menthone depolarization remained after washing. The interaction of monoterpenoids with membrane permeability and ion channel-blocking will be discussed. The physiological, biochemical, metabolic and allelopathic effects of peppermint oil and oil components on cucumber root system are discussed along with general considerations on other higher plants.
Citazione: Maffei M (1999). Effetti allelopatici degli oli essenziali di Mentha piperita L. . 2° Congresso Nazionale SISEF, Bologna, 20 – 22 Ott 1999, Contributo no. #c2.6.22