The inhibitory effect of Ca2+ on the flavonoid production of Tetrastigma hemsleyanum suspension cells induced by metal elicitors

Abstract

Tetrastigma hemsleyanum suspension cells were treated with four metal salts to screen suitable elicitors for the promotion of plant cell biomass and flavonoid production. The effects of calcium ions (Ca2+) on induction were also studied. It was found that the most effective elicitors were 50 μM of the heavy metal ion copper (Cu2+) and 100 μM of the rare earth element cerium (Ce3+). The maximal biomass levels under respective treatments over a 16-d culture period increased by 1.3- and 1.6-fold, and the total flavonoid content was 1.8- and 1.6-fold greater than the control, respectively. Reducing the exogenous Ca2+ concentration or adding Ca2+ antagonists (1 mM ethylene glycol-bis(2-aminoethylether)-N,N,N′,N-tetraacetc acid (EGTA) or 1 mM verapamil) strengthened inductive effects of metal elicitors and enhanced flavonoid production. However, 0.5 μM of the calcium ionophore A23187 showed contrary results. The increase in exogenous Ca2+ concentration in the presence of A23187 suppressed H2O2 bursts and peroxidase activity caused by metal elicitors. The results suggest that Ca2+ plays an inhibitory role in the plant cell response to metal elicitors. This suppression could have been caused by Ca2+ preventing the cells from absorbing metal ions and then easing the induction, or because the decrease of Ca2+ concentration worked as an induction signal. Therefore, reducing the Ca2+ concentration in culture medium, or adding Ca2+ antagonists could be used to improve flavonoid production and cell growth in combination with induction by metal elicitors during in vitro culture of T. hemsleyanum suspension cells.