Prolonged incubation of callus on auxin herbicide 2,4-D displayed significant effect on alkaloid production in callus of the woody medicinal plant Polyalthia bullata

The production of alkaloids in the intact plant is usually low, and some of them are tissue-specific and growth stage–specific. In this study, the total alkaloid content (TAC) in Polyalthia bullata was determined using different extraction solvents, and the extracts were subjected to LC-MS analysis. The manipulation of alkaloid production in P. bullata callus was further carried out by growing the callus on two basal media (Murashige and Skoog (MS) and Woody Plant Medium (WPM)) containing auxins (2,4-dichlorophenoxyacetic acid (2,4-D), α-naphthaleneacetic acid (NAA), 4-amino-3,5,6-trichloropicolinic acid (picloram), 3,6-dichloro-o-anisic acid (dicamba), indole-3-acetic acid (IAA), and indole-3-butyric acid (IBA)), precursors (L-phenylalanine, L-tyrosine, and L-tryptophan), and elicitors (methyl jasmonate (MeJA), salicylic acid (SA), and chitosan). The methanolic extracts exhibited the highest alkaloid content in leaf, stem, and root tissues (4.61 ± 0.04 to 7.71 ± 0.04 mg/g DW), and nine alkaloids were detected in P. bullata. The callus grown on MS + 30 μM 2,4-D exhibited the highest alkaloid accumulation (31.07 ± 0.05 μg/mg DW) after 6 weeks of culture compared to other media: MS media containing auxins, MS media containing auxins and precursors, and MS media containing auxins and elicitors. Therefore, we conclude that the MS + 30 μM 2,4-D is potent in enhancing alkaloid production in P. bullata callus.