Enhancement of Shikalkin Production in Arnebia euchroma Callus by a Fungal Elicitor, Rhizoctonia solani

There is a growing demand for mass production of shikalkin (a natural pigment consisted of shikonin and alkannin) due to its increasing applications in cosmetics, pharmaceutical and nutrition industries. The root of Iranian Arnebia euchroma produces shikalkin. The promising capability of this plant for shikalkin production has already been demonstrated in cell culture studies. Elicitation effect of Rhizoctonia solani (R. solani) in comparison with the effects of Cu2+, methyl jasmonate (MJ), and salicylic acid (SA) on the shikalkin production was investigated in A. euchroma callus. The calli from different origins (leaf, collar and root) were proliferated on a modified Linsmaier-Skoog (mLS) medium and were subsequently transferred onto the pigment production medium containing various amounts of the desirable elicitor. Observations were quantified and the pigment production was precisely measured spectrophotometrically. Pigment biosynthesis was induced on White medium containing IAA (1 mM) and kinetin (10 mM) in dark at 25°C. Use of R. solani increased the pigment production by 7 fold greater than normal White medium. Cu2+ only doubled the shikalkin production. MJ and SA showed enhancing effects comparable to that of Cu2+. It is assumed that upon binding of the polysaccharides of the fungal cells to the plant cell surface, a cascade of signaling is initiated that led to expression of genes involving in the biosynthesis of shikalkin.