Optimization of factors affecting Agrobacterium-mediated hairy root induction in Vitex negundo L. (Lamiaceae)

Vitex negundo L. is an aromatic, woody, blooming shrub in the Verbenaceae family which can grow into a small tree. Traditionally, V. negundo root has been used to cure diabetes, colic, boils, leprosy, and rheumatism. Keeping the importance of its roots in mind, an attempt has been taken for development of a protocol for efficient hairy root proliferation system. The Agrobacterium rhizogenes strains (MTCC 532 and MTCC 2364) were used for hairy root induction. For A. rhizogenes infection, both in vitro and in vivo leaves as well as internodes were used as explant. In vitro leaves and internodal explants were obtained by the inoculation of matured nodal segments on the optimum medium [MS + 2.0 mg/L N6-Benzylaminopurine (BAP)] with c.a. 91.6% shoot regeneration and an average of 8.1 shoots per explants. In vitro leaf showed best hairy root induction followed by in vitro internode on ½ MS medium augmented with acetosyringone. Highest transformation efficiency was achieved using MTCC 2364 strain, while no transformation was observed in MTCC 532 strain. Different factors affecting transformation including co-cultivation period, infection time and optical density (O.D.) value were standardized. The highest efficacy, 88.8% hairy root induction was observed in in vitro leaves infected by MTCC 2364 for 60 minutes infection time with an O.D. value of 0.29 maintained over a 44-48 hours of co-cultivation period. The prescribed protocol may be used as a reference for development of industrial scale hairy root production for bioactive compound located in root of V. negundo.