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Traditional Chinese medicine (TCM) belongs to the most elaborate and extensive systems of plant-based healing. The herb Northern Ban Lan (Isatis tinctoria) is famous for its antiviral and anti-inflammatory activity. Although numerous components isolated from I. tinctoria have been characterized so far, their modes of action have remained unclear. Here, we show that extracts from I. tinctoria exert antimicrotubular activity. Using time-lapse microscopy in living tobacco BY-2 (Nicotiana tabacum L. cv Bright Yellow 2) cells expressing green fluorescent protein-tubulin, we use activity-guided fractionation to screen out the biologically active compounds of I. tinctoria. Among 54 fractions obtained from either leaves or roots of I. tinctoria by methanol (MeOH/H 2 O 8:2), or ethyl acetate extraction, one specific methanolic root fraction was selected, because it efficiently and rapidly eliminated microtubules. By combination of further purification with ultrahigh-performance liquid chromatography and high-resolution tandem mass spectrometry most of the bioactivity could be assigned to the glucosinolate compound glucobrassicin. Glucobrassicin can also affect microtubules and induce apoptosis in HeLa cells. In the light of these findings, the antiviral activity of Northern Ban Lan is discussed in the context of microtubules being hijacked by many viral pathogens for cell-to-cell spread.

Weed control tries to suppress competitors for a crop and often relies on differential intoxication, making use of differences in uptake, development, or metabolism. We explored the possibility of using natural signals to shift competition in favour of the crop. Using the competitive horsemint (Mentha longifolia) as a paradigm, we showed that essential oils from certain mint species suppress the seedling development of different target species in a specific and efficient manner. The specificity concerned both the donor and the receptor. We demonstrated further that the effect of horsemint oil was specific for actin filaments, and not for microtubules. Since the elimination of actin will impair auxin transport, which is essential for root regeneration in vegetatively propagating weeds, we tested the efficacy of horsemint essential oil in combination with a slow-release carrier against field bindweed (Convolvulus arvensis), a pertinent weed in organic cereal production. We observed that the development of this weed can be specifically blocked, especially if the carrier is worked into the soil. We propose that allelopathic interactions, often relying on manipulative chemical signalling, harbour significant potential for organic weed control.