Accumulation of salicylic acid-elicited alkaloid compounds in in vitro cultured Pinellia ternata microtubers and expression profiling of genes associated with benzoic acid-derived alkaloid biosynthesis

The alkaloid compounds found in Pinellia ternata tubers have major bioactive components, and thus, these plant products are one of the most widely used ingredients in traditional Chinese medicines (TCMs). Under field agricultural growth conditions, however, it usually takes 2 years for tuber formation and growth. In vitro induced microtubers provide an alternative approach for the commercial production of P. ternata tubers for use in the TCM industry. The elicitation effect of supplementation with salicylic acid (SA) on the accumulation of alkaloid compounds in tubers and the related molecular regulation mechanism for biosynthesis are not well understood. In this study, we address this knowledge-gap through the development of an efficient induction system of in vitro cultured microtubers subsequently used to study the mechanism for elicitation of alkaloid compound accumulation by SA. Efficient microtuber induction was achieved by inserting petioles inversely into solid Murashige & Skoog medium (MS) followed by subculturing the morphologically expanded lower portion of the culture petioles in suspension culture, without the additional application of plant growth regulators. The in vitro microtuber induction rate achieved was 100% within 25 days of culture. When treated with 50–150 μM of SA, in vitro cultured microtubers showed higher accumulation of alkaloid compounds over the negative control. The highest accumulation detected showed an increase of 2.5-, 2.1-, 2.8-, and 3.1-fold in the concentration of total alkaloid compounds, guanosine, inosine and ephedrine, respectively, in the presence of 100 μM SA, 15 days after induction. qRT-PCR analysis of candidate genes for key enzymes in alkaloid biosynthesis indicated that CNL, CHY and BALDH are most probably responsible for the accumulation of benzoic acid and other alkaloid derivatives in the in vitro cultured microtubers following SA elicitation. This study developed an efficient in vitro microtuber induction system, and used this to determine that SA-promoted accumulation of alkaloids is associated with genes in the benzoic acid and alkaloid derivative biosynthesis pathway in P. ternata.