Abstract
Xanthanolides from Xanthium strumarium L. exhibit various pharmacological activities and these compounds are mainly produced in the glandular trichomes of aerial plant parts. The regulation of xanthanolide biosynthesis has never been reported in the literature. In this study, the effects of phytohormonal stimulation on xanthumin (a xanthanolide compound) biosynthesis, glandular trichomes and germacrene A synthase (GAS) gene expression in X. strumarium L. young leaves were investigated. The exogenous applications of methyl jasmonate (MeJA), indole-3-acetic acid (IAA), and gibberrellin A3 (GA3) at appropriate concentrations were all found to improve xanthumin biosynthesis, but in different ways. It was suggested that a higher gland density stimulated by MeJA (400 µM) or IAA (200 µM) treatment caused at least in part an improvement in xanthumin production, whereas GA3 (10 µM) led to an improvement by up-regulating xanthumin biosynthetic genes within gland cells, not by forming more glandular trichomes. Compared to the plants before the flowering stage, plants that had initiated flowering showed enhanced xanthumin biosynthesis, but no higher gland density, an effect was similar to that caused by exogenous GA3 treatment.
Highlights
X. strumarium L. is an annual herb and its aerial parts have been used as a folk medicine to treat cancer, fever, headaches, leucoderma and skin pruritus [1]
X. strumarium L. is not the only plant species to produce xanthanolides, as these compounds are produced in other species including Helianthus annuus [6,7] and Carpesium longifolium [8], indicating that the biochemical basis of xanthanolide biosynthesis may be applicable to those species
Flowering development has been shown to positively influence gland formation and sesquiterpene production in A. annua L., which tempted us to investigate whether similar effects could be adapted to the X. strumarium L. species
Summary
X. strumarium L. is an annual herb and its aerial parts have been used as a folk medicine to treat cancer, fever, headaches, leucoderma and skin pruritus [1]. X. strumarium L. glandular trichomes, which are distributed from northern to southern areas of China. The regulation of xanthanolide biosynthesis in X. strumarium L. has never been reported in the literature. Flowering is an important plant development event affecting sesquiterpene biosynthesis. Gibberellins (especially GA3) are the key molecules that promote flowering development [16], and have been found to increase the formation of glandular trichomes [17] and sesquiterpene biosynthesis [14] in Arabidopsis thaliana plants. In this study, we examined the effects of flowering initiation and exogenous GA3 on the formation of glandular trichomes and the biosynthesis of xanthumin on X. strumarium L. young leaves. GA3, MeJA, and IAA were assessed for their effects on gland formation, xanthumin biosynthesis, and GAS gene expression in X. strumarium
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