Effects of abscisic acid on the secondary metabolism of cultured Onosma paniculatum cells.

ABA addition to B5 or M9 medium at the concentrations from 0.1 to 5.0 mg/l suppressed growth of Onosma paniculatum cells. The addition of these ABA concentrations to M9 medium also significantly decreased the formation of shikonin and its derivatives in the cultured cells during the entire course of culturing. The enzyme activity assay showed that, on the 4th day after inoculation, 0.1 mg/l ABA significantly decreased the activities of phenylalanine ammonia-lyase, the first enzyme, and p-hydroxybenzoic acid-geranyltransferase, a key enzyme involved in shikonin biosynthesis. However, no significant change in these two enzyme activities was found during the following days for testing (8, 12, and 16 days). Interestingly, RT-PCR analysis of the PAL1 and LePGT1 gene expression showed no significant changes on the 4th day after inoculation. Furthermore, we found that the inhibitory effect of ABA on the secondary metabolism could be alleviated significantly by the addition of 2-aminoethyl diphenyl borate (an inhibitor of inositol triphosphate-receptor) or nicotinamide (an inhibitor of ADP-ribose cyclase), which functions by decreasing the intracellular calcium concentration. [ABSTRACT FROM AUTHOR]