The effect of temperature and pH on biomass and bioactive compound production in Silybum marianum hairy root cultures

Background and objectives: The seed extract of Silybum marianum contains seven flavonolignans known collectively as silymarin. These metabolites can be produced in hairy root cultures of S. marianum. The effect of different physical factors can change root biomass and silymarin production which has been investigated in the present study. Methods: The effect of different physical factors of temperature (30 ºC/25 ºC, 25 ºC/25 ºC and 15 ºC/20 ºC in 16 h/8 h cycle) and pH (5, 5.7, 6 and 7) were evaluated with respect to the root biomass and silymarin production in hairy root cultures of the plant. Results: Incubation temperature, 25 ºC /25 ºC promoted the silymarin production in 4-week old hairy roots (0.18 mg/g DW) as compared with the cultures treated with 15 ºC/20 ºC and 30 ºC/25 ºC (0.13 and 0.12 mg/g DW, respectively). Maximal increases in biomass and silymarin accumulation occurred in the root cultures grown in pH 5 and 25 ºC/25 ºC (0.45 g and 0.26 mg/g DW). The content of silybin, isosilybin, silychristin, silydianin were 0.025, 0.024, 0.061 and 0.095 mg/g DW, respectively which were higher than those grown in higher pH. Conclusion: The results of the present study suggest that 25 ºC/25 ºC and acidic environment of medium are beneficial for silymarin production using hairy root cultures. Furthermore, lipoxygenase (LOX) activity was strongly affected by pH which suggested that acidic environment may act as inducing signal for LOX activity and subsequently greater silymarin production.