Effect of elicitor dosage and exposure time on biosynthesis of indole alkaloids by Catharanthus roseus hairy root cultures

Late exponential phase hairy root cultures of Catharanthus roseus were elicited with pectinase and jasmonic acid. The effects of elicitor concentration and exposure time on growth and levels of several compounds in the indole alkaloid biosynthetic pathway were monitored. Pectinase decreased the fresh weight to dry weight ratio of the roots, while addition of jasmonic acid had no significant effect. Selective effects on indole alkaloid yields were observed upon addition of elicitors. An increase of 150% in tabersonine specific yield was observed upon addition of 72 units of pectinase. Transient studies at the same level demonstrated possible catabolism as serpentine, tabersonine, and lochnericine levels decreased immediately after elicitation. The levels of these compounds recovered back to control levels or were higher than the control levels after some time. Jasmonic acid was found to be a unique elicitor leading to an enhancement in flux to several branches in the indole alkaloid pathway. Jasmonic acid addition caused an increase in the specific yields of ajmalicine (80%), serpentine (60%), lochnericine (150%), and horhammericine (500%) in dosage studies. Tabersonine, the likely precursor of lochnericine and horhammericine, decreased at lower levels of jasmonic acid and then increased with increasing jasmonic acid concentration. Transient studies showed that lochnericine and tabersonine levels go through a maxima, then decrease back to control levels and reduce below control levels, respectively. The yields of ajmalicine, serpentine, and horhammericine increased continuously after the addition of jasmonic acid. The methods described in this article could generally be used in devising strategies for enhancement in productivity of secondary metabolites and for probing and studying the complex secondary metabolite pathways in plant tissue cultures.