Secondary metabolism in micropropagated Hypericum perforatum L. grown in non-aerated liquid medium

Hypericum perforatum L. is a medicinal plant that has been extensively studied because of its bioactive properties. The objective of this study was to establish a system that could lower the cost of in vitro propagation by using liquid medium, as well as to evaluate the secondary metabolism in the systems tested. Nodal segments of H. perforatum were obtained from in vitro shoots and grown in three liquid culture systems: total immersion (TI), partial immersion (PI), and paper bridge support (PB). Semi-solid medium (3 g L-1 Phytagel (TM)) was used as control (SS). The organogenic responses were evaluated, and phenolic compounds, hypericin, and the activity of polyphenol oxidases (PPO) and peroxidases (POX) were quantified. After 80 days of culture, induction and proliferation of adventitious shoots were similar in the PI and SS systems (65.3 and 71.3 shoots, respectively), whereas PB resulted in the fewest shoots per explant (29.5 shoots). Longer shoots were obtained under the PI conditions. Hyperhydricity was observed in the shoots from the TI system. Browning was visible in shoots from the TI and PB systems. The highest concentrations of phenolic compounds and hypericin were observed in shoots derived from PI and PB, at 80 days of culture. POX activity was higher in shoots cultured in PI at 40 days, whereas PPO was significantly more active at 80 days of culture. Likely, POX was more related to shoot growth, whereas PPO played a later role in response to the culture environment and medium stress.