Alkaloid production of Cinchona officinalis (”Ledgeriana”) hairy root culture containing constitutive expression constructs of tryptophan decarboxylase and stryctosidine synthase cDNAs from Catharanthus roseus - Geerlings,A.; Hallard,D.; Martinez Caballero,A.; Lopez Cardosi,I.; van der Heijden,R.; Verpoorte,R. (Plant Cell Rep, 1999)