SCOPOLIN A GLYCOSIDE FORM OF THE PHYTOALEXIN SCOPOLETIN IS LIKELY INVOLVED IN THE RESISTANCE OF NICOTIANA ATTENUATA AGAINST ALTERNARIA ALTERNATA
J. Li, J. Wu
Phenolic coumarins are secondary metabolites playing an important role in plant-environment interaction. Previously, we have shown that wild tobacco Nicotiana attenuata accumulates high amounts of the jasmonate (JA)-dependent phenolic coumarin, scopoletin, as a phytoalexin to defend itself against a necrotic fungal pathogen, Alternaria alternata (tobacco pathotype). Scopolin, a ß-glycoside form of scopoletin, was strongly elicited and to a level even higher than that of scopoletin in host plants after A. alternata infection. However, it was not known whether scopolin functioned as a phytoalexin playing a role in the resistance or simply as a storage form of scopoletin. When supplied in PDA medium, scopolin exhibited a moderate but slightly weaker anti-fungal activity against A. alternata than that of scopoletin. In addition, A. alternata-elicited scopolin level was dramatically decreased in JA deficient plants. Thus, all the data suggest that scopolin is also a JA-dependent phytoalexin likely involved in the resistance of N. attenuata against A. alternata.