Root samples were extracted as describe by Monforte-González et al. {Monforte-González, 1992 8553 /id /d}. Briefly, lyophilized root tissue (0.5 g) was resuspended in 6 mL methanol (67561, JT Baker) and incubated into a water bath at 50ºC for 2 h.
   The methanolic extracts obtained were concentrated under vacuum. The residue was resuspended in 10 mL of sulphuric acid (2.5%, v/v; 7664939, Fermont) and extracted three times with 10 mL of ethyl acetate (141786, Merck). The pH of the remaining aqueous solution was adjusted to 9.5 with concentrated ammonium hydroxide (28%, v/v; 1336216, Fermont) and extracted with 10 mL of ethyl acetate three times.
   This last organic phase extractions were pulled together, concentrated under vacuum and resuspended into 600 µL of methanol and stored for total alkaloid determination.
   For the extraction of the alkaloids from the culture medium, this was lyophilized, resuspended with 7.5 mL of sulphuric acid (2.5%, v/v) and then the same previous protocol was followed.
   Total alkaloid contend was determine measuring the sample’s absorbance at λ= 280 nm {Lee, 1981 10644 /id}; this value was compared with a standard curve of mixture of known alkaloids (0 - 75 µg alkaloids mL-1).
   The mixture of alkaloids (total volume = 1 mL) was composed of ajmalicine (2 µg), ajmaline (2 µg), vincamine (1 µg), vindoline (1 µg), catharanthine (2 µg) and yohimbine (2 µg).