Synergistic effects of polyploidization and elicitation on biomass and hyoscyamine content in hairy roots of Datura stramonium

Description of the subject. The hyoscyamine, a tropane alkaloid, widely used in medicine, can be produced from Datura sp. (Solanaceae). However, its content in the spontaneous roots remains low; therefore, hairy roots (HRs) were envisaged as a potential alternative to improve its biosynthesis. The hairy roots are characterized by a good genetic stability and a rapid growth. Indeed, Datura stramonium HRs have widely been studied in the perspective of improving the yield of hyoscyamine. This study is part of this same perspective. Objectives. This paper aims to study the effects of polyploidization of HRs induced by colchicine in synergy with elicitation (with acetylsalicylic [ASA] or salicylic acids [SA]) on the hyoscyamine content in D. stramonium. Method. Colchicine was applied at different concentrations and periods, on a selected hairy root line (LDS) of D. stramonium obtained by infection with Agrobactrium rhizogenes strain A4. The selection of tetraploid HR lines was performed by the cytogenetic analysis using light microscopy. The effect of polyploidization and elicitation was studied on the biomass (dry weight) and hyoscyamine content of HRs. Results. The untreated HR line (control) shows a diploid level with 2n = 24 chromosomes. However, the HR lines treated with colchicine show, in most cases, an endoreduplication of their genetic material. The survival rate of endoreduplicated lines varies between 30% and 93%, depending on concentration and exposure time to colchicine. Moreover, the tetraploid HR line shows an increase in its biomass and hyoscyamine content in comparison to the diploid HR line (LDS). Further, elicitation of HRs by ASA or AS at the 10-4 M concentration causes a low decrease or increase in dry weight, respectively. However, the same treatments show a significant increase in the yield of hyoscyamine in elicited HR lines. Consequently, our work indicates that the combination of polyploidy and elicitation can lead to significant improvements in hyoscyamine biosynthesis and content due to their synergistic effects. Conclusions. Elicitation of tetraploid hairy root lines improves significantly their content of hyoscyamine