Elicitor induction of furanocoumarin biosynthetic pathway in cell cultures of Ruta graveolens

Treatment with an autoclaved culture homogenate of the yeast Rhodotorula rubra induces rapid accumulation of acridone epoxides, furoquinolines and furanocoumarins in cell cultures of Ruta graveolens (L). The increased accumulation is preceeded by an induction of enzymes of the biosynthetic pathways. In the case of furanocoumarins induction was shown for phenylalanine ammonia-lyase (PAL), 4-coumarate: CoA ligase (4-CL) and S-adenosyl-L-methionine: xanthotoxol O-methyltransferase (XOMT). For PAL and 4-CL time courses of induced activity showed an early maximum, 8-12 h after treatment, whereas XOMT was found to reach its maximum later, about 36-42 h after treatment. The elicitor dose-response curve showed saturation at an elicitor concentration of 1%. At any time during the whole culturing period cells responded to elicitiation but the maximum enzyme activities induced were lower at the late stages. Experiments with different suspension culture strains, a shoot teratoma culture and hydrcponically grown sterile photomixotrophic plants were performed to assess the influence of differentiation on constitutive activities of these enzymes and their inducibility by elicitation. Constitutive furanocoumarin accumulation was positively correlated with the level of differentiation. Although induction of PAL, 4-CL and XOMT activity always accompanied induced furanocoumarin accumulation no absolute correlation existed between induced enzyme activities and the induced product level or relative product increase.