A novel microfloating culture system for the in vitro rooting of Echinacea angustifolia D.C.: photosynthetic performance and production of caffeic acid derivatives

The in vitro rooting phase of Echinacea angustifolia DC. was studied through an unconventional approach, where micropropagated shoots from adult plants were grown under autotrophic conditions. The system employed artificial supports (cellulose plugs) soaked with a liquid sugar-less MS medium that contained 1 mg L−1indole-3-butyric acid (microfloating). The culture vessels were provided with passive ventilation (PV) or forced ventilation (FV) by bubbling air into the liquid medium. Using this microfloating system, the E. angustifolia plantlets reached about 65% rooting capacity. The cultures were analyzed for their photosynthetic rates (PN), carbohydrate content and phytochemical profile. When the ventilation of the vessels was forced, the net photosynthetic rate was enhanced improving explant quality and survival during acclimatization, but the content of caffeic acid derivatives (CADs) was negatively affected. On the contrary, at the end of the multiplication phase in mixotrophic conditions, the photosynthesis was impaired and the production of CADs was improved. The mixotrophy or autotrophy status experienced by the E. angustifolia microplants during the micropropagation process can direct the cultures towards either the accumulation of active compounds or the production of good quality transplants suitable to undergo the acclimatization process