5‐Aminolevulinic acid promotes callus growth and paclitaxel production in light‐grown Taxus cuspidata suspension cultures

Cultured plant cells generally produce low levels of secondary metabolites, and elicitors of secondary metabolites usually inhibit callus growth. The aim of this study was to determine the effect of 5‐aminolevulinic acid (ALA), a chlorophyll precursor that promotes plant growth, on callus induction from leaves of Taxus cuspidata, and on callus growth on solid medium. ALA at 0.76, 7.6, and 76 μM had similar effects on callus induction and growth, while ALA at 760 μM had negative effects. Next, the effects of ALA concentrations on callus growth and paclitaxel production in suspension cultures in the dark were evaluated. The results showed that 0.76 and 7.6 μM ALA stimulated growth and paclitaxel production, while 76 μM ALA had negative effects. ALA is thought to promote cellular activity under light conditions. Therefore, the effects of light intensity on callus growth and paclitaxel production in the presence of ALA were evaluated. Our results showed that the best conditions for callus growth and paclitaxel production were 7.6 μM ALA under photosynthetically active radiation of 12 μmol photons m^?2 s^?1. Callus growth and paclitaxel production were inhibited under stronger light (24 μmol photons m^?2 s^?1). Together, these results show that ALA promoted callus growth and the production of paclitaxel by light‐grown cultured T. cuspidata cells.