Wanda Camusso

Effect of Mentha × piperita essential oil and monoterpenes on cucumber root membrane potential

Peppermint (Mentha piperita L.) essential oil and its main components were assessed for their ability to interfere with plant plasma membrane potentials. Tests were conducted on root segments isolated from etiolated seedlings of cucumber (Cucumis sativus L.). Increasing the concentration of peppermint essential oil from 5 to 50 ppm caused a decrease in membrane potential (Vm) hyperpolarization of 10-3 mV, whereas concentrations from 100 up to 900 ppm caused an increasing depolarization of Vm (from 5 to 110 mV). When tested at 300 ppm, (+)-menthyl acetate, (-)-limonene and 1,8-cineole did not exert any significant effect on V(m), whereas (+)-menthofuran (73 mV), (+)-pulegone (85 mV), (+)-neomenthol (96 mV), (-)-menthol (105 mV) and (-)-menthone (111 mV) showed increased ability to depolarize V(m). A plot of log of octanol-water partition coefficient (K(ow)) against their depolarizing effect showed a significant negative correlation, suggesting that among all monoterpenoids increased membrane depolarization depends on lower K(ow). However, among monoterpene ketones, alcohols and furans, increased membrane depolarization is associated with a decline in water solubility. The possible effect of monoterpenoids on membrane ion fluxes is also discussed, since changes in the bioelectric potential of cells imply changes in the flux of ions across the plasma membrane

Effect of (+)-pulegone and other oil components of Mentha x Piperita on cucumber respiration.

Peppermint (Mentha x piperita L.) essential oil and main components were assessed for their ability to interfere with plant respiratory functions. Tests were conducted on both root segments and mitochondria isolated by etiolated seedlings of cucumber (Cucumis sativus L.). Total essential oil inhibited 50% of root and mitochondrial respiration (IC50) when used at 324 and 593 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), whereas (-)-menthol was the less inhibitory compound (IC50 values of 1.85 and 3.80 mM respectively). A positive correlation was found for (+)-pulegone, (-)-menthone and (-)-menthol between water solubility and respiratory inhibition. The uncoupling agent. carbonyl-cyanide-m-chlorophenyl-hydrazone (CCCP), lowered (-)-menthol and (-)menthone inhibition and annulled (+)-pulegone inhibition of mitochondrial respiration, whereas salicyl-hydroxamic acid (SHAM) 2-hydroxybenzohydroxamic acid, the alternative oxidase (AO) inhibitor, increased (-)-menthone inhibition and annulled both (+)-pulegone and (-)-menthol 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.

Fructose is the most uptaken sugar for (-)-carvone biosynthesis in Mentha spicata L.

Summary Mentha spicata L. cuttings were fed in vivo with 14 C-palmitate, 14 C-acetate, 14 C-sucrose, 14 C-glucose, and 14 C-fructose. No labelled (-)-carvone was detected when cuttings were fed with 14 C-palmitate and/or 14 C-acetate, whereas feeding of cuttings with 14 C-sucrose, 14 C-glucose, and 14 C-fructose resulted in labelled (-)-carvone biosynthesis. Among sugars, fructose feeding caused the highest (-)-carvone biosynthesis. The lack of incorporation of exogenous 14 C-palmitate and/or 14 C-acetate into (-)-carvone and the incorporation of sugars into this monoterpene, also confirm for this species the presence of an alternative, non-mevalonate biosynthetic pathway for monoterpene production.

In vitro interactions between Mentha piperita L. and a non-mycorrhizal endophyte: root morphogenesis, fungus development and nutritional relationships

Abstract Field grown Mentha piperita can be colonized by a fungal endophyte, PGP-HSF, which heavily infects roots and enhances growth of in vitro grown plants. In this work, the time course of fungal development and its morphogenetic effects on plant growth, as well as phosphorus shoot concentration, were analyzed. Fungal infection induced longer shoots and roots and increased adventitious root branching. Microscopic analyses showed that hyphae grew between the walls of rhizodermal cells, produced a progressively thicker sheath and colonized the senescent rhizodermal cells. Plant mechanical defences developed early after the contact between hyphae and rhizodermal cells, and specialized host-fungus interfaces were not observed. Phosphorus concentration was lower in colonized plants than in controls. Our data support a passage of carbon from the plant to the fungus, but no transfer of mineral nutrients from the fungus to the root. The role of PGP-HSF on the enhancement of host growth is discussed.

Effect of benzoic acid hydroxyl- and methoxy-ring substituents on cucumber (Cucumis sativus L.) root membrane potential

Abstract The allelopathic effect of some benzoic acid (BA) OH- and OCH3-ring substituents was studied on cucumber root transmembrane potential difference (Vm). Most of the methoxy-BAs induced a rapid Vm depolarization, followed by a Vm hyperpolarization, with the only exception for p-anisic acid (pA). On the other hand, salicylic acid (SA) and 3,4-dimethoxybenzoic acid (DHB) strongly depolarized Vm. A positive correlation was found between Vm hyperpolarization and lipophilicity of methoxylated BAs, whereas a positive correlation was found between lipophilicity and Vm depolarization of hydroxylated BAs. The influence of BAs on K+ was studied by means of specific blocking with Cs+ indicating a possible direct interaction of SA, gallic acid (GA), vanillic acid (VA) and 3,4-dimethoxybenzoic acid (DMB). Interference of BAs with the Vm hyperpolarizing effect of root perfusion with the fungal toxin fusicoccin were also observed.

Sugar metabolism of Vetiveria zizanioides cells cultured with Amberlite XAD-4. Uptake of radiolabelled sugars, cell wall invertase activity and gene expression

Abstract Activated and non-activated Amberlite XAD-4 was added to the cell cultures of vetiver (Vetiveria zizanioides Stapf.) in order to study its effects as abiotic growth promoter. Amberlite XAD-4 increased vetiver cell viability, especially when used in the activated form. Results from labelling experiments in cell suspensions showed that XAD-4 prompted a significant decrease of sucrose Km, accompanied by an increased Vmax. Glucose uptake from the medium was almost doubled, as demonstrated by the increase of the radiolabelled fraction (25-fold the controls) in vetiver cells cultured with XAD-4. Affinity for fructose uptake by cells was not altered by the use of activated XAD-4, even though its uptake and Vmax increased. These results were further supported by a significant 7.5-fold increase in cell wall invertases (CWI) activity in XAD-4 elicited cells. Vetiver CWI gene expression was characterized by transcript RT-PCR analysis. The identity of the transcripts was confirmed by sequencing analysis. These results indicated the use of XAD-4 as an effective tool for vetiver cell biomass optimization.

The C4 biochemical pathway, and the anatomy of lemongrass (Cymbopogon citratus (DC) Stapf.) cultivated in temperate climates

ABSTRACT Leaf anatomy (light and transmission electron microscopy, immunogold localisation of Rubisco) and physiology (C4 photosynthetic enzyme activities, CO2 assimilation and stomatal conductance) were studied in lemongrass, Cymbopogon citratus (DC) Stapf., cultivated in temperate climates (northwestern Italy). The leaf blade had an NADP-ME Kranz anatomy, with bundle sheath cells containing chloroplasts located in a centrifugal position. Dimorphic chloroplasts, agranal and starchy in the bundle sheath and granal starchless in the mesophyll cells, were also observed. Rubisco, as determined by immunolocalisation, occurred only in the bundle sheath chloroplasts. Pyruvate, orthophosphate dikinase (PPDK), NADP malic dehydrogenase (NADP-MDH), NADP malic enzyme (NADP-ME), PEP-carboxykinase (PCK), and NAD malic enzyme (NAD-ME) activities were also measured, indicating an NADP-ME C4 photosynthetic pathway. Some kinetic properties and chemicalphysical parameters of lemongrass NADP-ME and NADP-MDH as well as CO2 compensation point and stomatal conductance values confirmed these preliminary data. C. citratus appeared to be well adapted to the varying environmental conditions typical of temperate climates, by retaining high NADP-MDH and NADP-ME activities and a low CO2 compensation point.

Evidence for a C4 NADP-ME photosynthetic pathway in Vetiveria zizanioides Stapf

ABSTRACT Leaf anatomy (light and transmission electron microscopy), immunogold localization of Rubisco, photosynthetic enzyme activities, CO2 assimilation and stomatal conductance were studied in Vetiveria zizanioides Stapf., a graminaceous plant native to tropical and subtropical areas, and cultivated in temperate climates (Northwestern Italy). Leaves possess a NADP-ME Kranz anatomy with bundle sheath cells containing chloroplasts located in a centrifugal position. Dimorphic chloroplasts were also observed; they are agranal and starchy in the bundle sheath and granal starchless in the mesophyll cells. Rubisco immunolocalization studies indicate that this enzyme occurs solely in the bundle sheath chloroplasts. Pyruvate-orthophosphate dikinase, NADP-dependent malate dehydrogenase (NADP-MDH), NADP-dependent malic enzyme (NADP-ME), PEP-carboxykinase and NAD-dependent malic enzyme (NAD-ME) activities were determined. Enzyme activity and some kinetic properties of NADP-ME and NADP-MDH as well as CO2 compensation point and stomatal conductance values were calculated indicating a NADP-ME C4 photosynthetic pathway. Biochemical and structural results indicate that V. zizanioides belongs to the C4 NADP-ME variant. This plant appears to be well adapted to the varying environmental conditions typical of temperate climates, by retaining high enzyme activities and a low CO2 compensation point.