Volatile Terpenoids of Endophyte-free and Infected Peppermint (Mentha piperita L.): Chemical Partitioning of a Symbiosis
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The study reports the effects on volatiles of an endophytic fungus inhabiting asymptomatically the leaves of peppermint. By means of headspace solid-phase microextraction (HS-SPME) and gaschromatography-mass spectrometry (GC-MS) terpenoids were sampled in time course from the head space of peppermint leaves and roots. After removal of the mycelium from peppermint tissues, fungal volatiles were analyzed and compared with those of pure fungal cultures. In the presence of the endophyte, the relative amount of all main compounds increased in leaves. Starting from the first 14 d of culture, (−)-menthone and (+)-neomenthol were consistently higher than in control plants. On the contrary, (+)-menthofuran increased only by 28 d of culture. Root volatiles were also dramatically altered by the presence of the fungus, with (+)-pulegone accounting for at least 44% of the total volatile emission. (+)-Pulegone was also the main compound of PGP-HSF mycelium isolated from peppermint roots. The sesquiterpenoid cuparene was found as a novel compound of peppermint leaf headspace and was a main volatile of ex planta and pure culture mycelia. The chemical spectrum of terpenoids and their distribution among peppermint roots, leaves, and mycelia are likely to account for a fine regulation of the mutualism in planta and for the acquisition by the fungus of novel metabolic competences.
KeywordsArbuscular Mycorrhizal SPME Terpene Terpenoid Limonene
The authors wish to thank all the students and graduated students who gave technical support to this work. This research project was supported by a MURST 60% grant.
This article is dedicated to the memory of prof. Silvano Scannerini who first addressed our interest to the microbial communities of peppermint leaves and largely contributed to the critical revision of these results.
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