Effect of fungal elicitation on indirubin production from a suspension culture of Polygonum tinctorium

Six fungal elicitors were examined to determine their effects on the production of indirubin from a cell culture of Polygonum tinctorium. Cell wall-released heat-soluble elicitor prepared from Rhizoctonia solani was found to give an increase in the specific indirubin content by 168% of the unelicited cells. Indole at a 5 mM concentration was added as a precursor. Effects of elicitation conditions on indirubin production were also investigated. The optimum concentration of elicitor was 10 mg carbohydrate equivalent l^-1 medium with a 190% increase in specific indirubin content compared to the control. The treatment period of elicitor with P. tinctorium cells was most favorable at 3 days with a 104% increase compared to that at 28 days. There was a slight increase of 20% when both the elicitor and precursor were added in the production medium on day 7. The optimum sucrose concentration in the medium was 3%, it gave the specific indirubin content of 3.05 mg g^-1 dry cell weight (DCW). A double strength of calcium resulted in a 143% increase in specific indirubin content. Single strengths of potassium, phosphate, and magnesium concentrations were effective with the specific indirubin levels at 3.07, 2.87, and 2.79 mg g^-1 DCW, respectively. As a source of nitrogen, potassium nitrate was more effective than ammonium phosphate or the combination of the two salts. The specific indirubin level at pH 5.7 was 4.99 mg g^-1 DCW which was higher than the other pH conditions tested.