Production of Dihydroisocoumarins by Callus Induction from Hydrangea macrophylla var. thunbergii Leaves

Dihydroisocoumarins, hydrangenol 8-O-β-D-glucopyranoside (1), phyllodulcin 8-O-β-D-glucopyranoside (2), hydrangenol (3), and phyllodulcin (4), are well-known as the major secondary metabolites in the leaves of Hydrangea macrophylla var. thunbergii. Dihydroisocoumarins are pharmaceutical compounds with diverse bioactivity. Although dihydroisocoumarins are commonly isolated from Hydrangea plants or via organic chemical synthesis, their production via callus induction is considered a promising alternative. In the present study, callus induction and proliferation of H. macrophylla var. thunbergii, and constituents 1-4 were quantified in calluses cultured in 17 different media. We found that the combination of the phytohormones 2,4-dichlorophenoxyacetic acid (2,4-D) and 6-benzylaminopurine (BA) was useful for callus proliferation in H. macrophylla var. thunbergii. The balance and concentrations of indole-3-acetic acid (IAA) and BA greatly affected the contents of 1-4. Particularly, 1 (2.03-3.46% yield from the dry callus) was successfully produced from the callus induced by IAA (0.5 mg/L) and BA (1.0 mg/L) at yields comparable to isolated yields from plants. To the best of our knowledge, this is the first study to show that the calluses of H. macrophylla var. thunbergii contained 1. These findings may be useful for producing bioactive dihydroisocoumarins.