Ultrasound-assisted extraction of five anthraquinones from Rheum palmatum water extract residues and the antimicrobial activities

Previously studies found that Rheum palmatum L. water extract residues contains the abundant five anthraquinones, and could be used as a renewable source to enrich active compounds for industrial uses. In this paper, we found that the ultrasound- assisted extraction method could be used to enrich five anthraquinones from R. palmatum water extract residues; in addition, the extraction yields of this method were better than those of conventional extraction methods. Among of five anthraquinones, rhein had the strongest antifungal activity against Botrytis cinerea with an EC50 value of 8.28 μg/mL; it has marked preventative efficacy in vivo. RNA-Seq analysis and further studies showed that rhein significantly destroyed mitochondrial structure and functions, inhibited the tricarboxylic acid cycle and then blocked energy production to kill B. cinerea mycelia. This study laid the foundation for the further development of R. palmatum residues as a renewable source for anthraquinones extracted using the ultrasound-assisted extraction method, and rhein could be used as an alternative, environmentally friendly biofungicide.