Elicitation of tobacco alkaloid biosynthesis by disrupted spores and filtrate of germinating spores of the arbuscular mycorrhizal fungi Glomus etunicatum

Molecules released by soil microorganisms, such as arbuscular mycorrhizal fungi (AMF), trigger plant responses prior to any physical contact. Here, it is shown that disrupted spores (DS) homogenates and exudates from germinating spores (GS) of Glomus etunicatum caused marked alterations in the content of the tobacco alkaloids nicotine, anabasine, and nornicotine and the genes involved in their biosynthesis. GS and DS were applied to the base of Nicotiana tabacum seedling stems, and 3 or 10 days later, the leaves and roots were harvested for analyses. The alkaloid contents were influenced by both elicitors and varied depending on the harvest day. In general, such variations agree with the transcript levels of putrescine N-methyltransferase, oxide reductase A622 and nicotine N-demethylase CYP82E4. The results are discussed in light of recent insights on chemical signaling processes between plants and AMF able to trigger different elicitation responses and their possible effects on secondary metabolism in plants.