Growth regulators induced shoot regeneration and volatile compound production in Lippia rotundifolia Cham., a threatened medicinal plant

Lippia rotundifolia Cham. is an endemic and endangered plant found in the savanna that is aromatic and rich in monoterpenes. The aims of the study were to evaluate the influence of plant growth regulators on the growth and chemical analysis of L. rotundifolia by headspace/GC-MS. Nodal segments (1.0 cm) were cultured on basal Murashige & Skoog (MS) medium supplemented with the following amounts of growth regulators: 0.0, 2.22, 6.66, 11.10, and 15.54 mu M 6-benzylaminopurine (BAP) combined with 0.0, 2.68, and 5.36 mu M naphthaleneacetic acid (NAA) or 0.0, 2.27, 4.54, 6.81, and 9.08 mu M thidiazuron (TDZ) combined with 0.0, 2.68, and 5.36 mu M NAA. The most effective concentrations were 11.10 mu M BAP + 2.68 mu M NAA, which induced 11 shoots explant(-1), and 15.54 mu M BAP + 2.68 mu M NAA, with 11.6 shoots explant(-1). The TDZ at a concentration of 6.81 M with 2.68 mu M NAA resulted in 20 shoots explant(-1), 9.08 mu M TDZ without NAA in 22.8 shoots explant(-1), and 9.08 mu M TDZ + 2.68 mu M NAA in 18.1 shoots explant(-1). Rooting took place on MS medium free of plant growth regulators, and acclimatization was successful (95%). The influence of plant growth regulators on the fraction of volatile compounds appeared to be quite variable. The cytokinin concentration was found to significantly influence the production of volatile compounds in L. rotundifolia shoot cultures. These findings indicate that shoots regenerated from nodal segments on MS medium containing higher concentrations of BAP and NAA have increased myrcenone and limonene. Ocimenone contents increased only at low concentrations of BAP and NAA.