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Abstract Berberine is a naturally occurring plant secondary metabolite with allelopathic and cytotoxic properties. We investigated the cytotoxic effects of berberine against tobacco Bright Yellow-2 (BY-2) cells. We found that berberine inhibited tobacco BY-2 cell growth in a concentration-dependent manner and the potency of berberine was comparable to the traditional herbicide glyphosate. Meanwhile, the in vivo test revealed that the herbicidal activity of berberine was also comparable to that of glyphosate. Further mechanism studies for the cytotoxicity demonstrated that berberine at concentrations of 40 μg/mL and 80 μg/mL induced cell death by causing mitochondrial membrane depolarization, irregular nuclei and chromatin condensation but not leading to significant apoptosis. Ultra-structure analysis through transmission electron microscopy (TEM) indicated that treatments with 40 μg/mL berberine for 2 d or 80 μg/mL berberine for 1 d induced cell damage, including nuclei morphological changes, cytoplasm and mitochondria degradation and cell wall fibrosis. Treatment at higher concentration of 80 μg/mL for longer period of 2 d, induced plasmolysis and severe damage to basic cell structure, which are indicative of explosive necrosis. Our results suggest that berberine was cytotoxic to tobacco BY-2 cells by inducing necrosis but not apoptosis. Cell wall, mitochondria, nuclei and chromatin were damaged and may be possible primary targets. Therefore, the herbicidal activity of berberine appears to be a complex process associated with multiple mechanisms of action. Graphical abstract Unlabelled Image Highlights • Berberine inhibited tobacco BY-2 cell growth in a dose-dependent manner. • A complex process associated with multiple mechanisms of the action of berberine. • Cell wall, mitochondria, nuclei and chromatin may be possible primary targets. [ABSTRACT FROM AUTHOR]

The structure determination of the title compound, rotenone alpha-oxime [systematic name: 1,2,12,12a-tetrahydro-8,9-dimethoxy-2-(1-methylethenyl)-[1]benzopyrano[3,4-b]furo[2,3-h][1]benzopyran-6(6H)-one oxime], C(23)H(23)NO(6), confirms that the molecule has an approximately V-shaped structure. One of the rings has a typical cyclohexene-like monoplanar conformation and the central ring adopts a 1,2-diplanar conformation.