Elicitor-mediated enhanced accumulation of ursolic acid and eugenol in hairy root cultures of Ocimum tenuiflorum L. is age, dose, and duration dependent

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Ursolic acid (pentacyclic triterpene acid) and eugenol (phenolic compound), the major secondary metabolites of Ocimum tenuiflorum L., exhibit many pharmacological activities. Due to low quantities of these metabolites in the plant, it was imperative to apply biotechnological approaches for enhancing accumulation of these compounds. Effects of three elicitors namely yeast extract, methyl jasmonate, and salicylic acid were studied on the hairy root cultures induced by infecting leaves of O. tenuiflorum with Agrobacterium rhizogenes strain. The transgenic nature of hairy roots was validated by PCR of rolB gene. The yield of ursolic acid and eugenol responded to the age of the culture, the concentration of the elicitor and the incubation time. The 17-day-old hairy root cultures when treated with yeast extract (50 mg/L) produced the highest amount of ursolic acid of 1.56 mg/g dry weight (5.6-fold higher than control culture) and eugenol content of 0.41 mg/g dry weight (~6.0-fold higher than the control) after 8 days of exposure. Methyl jasmonate at 60 mg/L concentration also enhanced the accumulation of ursolic acid up to 1.43 mg/g dry weight (5.0-fold higher than the control) and eugenol up to 0.1 mg/g dry weight (1.55-fold higher than the control) after 8 days of elicitor treatment. Increased elicitor concentration and extended exposure time as well as age of the culture resulted in reduced accumulation of ursolic acid and eugenol in hairy root cultures. Our results demonstrate the importance of age of the culture, different exposure time, and concentration of elicitors in the hairy root culture of O. tenuiflorum for increased production of pharmaceutically important metabolites.