Elucidation of the effects of nitrogen source on proliferation of transformed hairy roots and secondary metabolite productivity in a mist trickling reactor by redox potential measurement

Nitrogen is the major limiting nutrient for most plant species. Production of high-quality protein is dependent on the availability of sufficient nitrogen. The aim of this work was to elucidate the effects of nutrients and nitrogen sources on the proliferation of transformed roots and secondary metabolite productivity in a mist trickling reactor (MTR). The effects of (NH4)2SO4 and KNO3 as well as the amino acids, their dosed concentrations and modes of application on the performance of hairy root culture were first studied in detail with 250 mL shake flask. The pertinent concentration of nitrogen source and nutrients were then determined. Although inconsistent results were observed between the shake flasks and MTR for l-DOPA content, reproducible effects of replenishment of NH4+ and sucrose from flask to MTR were obtained. On-line measurements of redox potential (Eh) together with some variables expressing the reactions involved during 16 day culture of hairy roots in a MTR revealed that the change of rH reflected the assimilations of NH4+, NO3−, sucrose and growth phases. The time course changes of Eh and rH corresponded to NH4+ and sucrose supplementation further supporting that the Eh and rH values reflected changes of nutrients and metabolism of hairy root growth.