Phenylpropanoid defence responses in transgenic Lotus corniculatus

Transformed root cultures of Lotus corniculatus L. cv. Leo were treated with a range of thiol and carbohydrate elicitors. Both thiol reagents and fungal carbohydrate preparations resulted in an increase in the activity of phenylalanine ammonia lyase (PAL) in a concentration-dependent manner. One representative thiol elicitor, glutathione (GSH), and one fungal elicitor, derived from Rhynchosporium orthosporum autoclaved cell walls (Ro), were analysed in more detail. Both elicitors induced the transient accumulation of vestitol, an isoflavan phytoalexin, in tissue and in culture medium. Treatment of Lotus root cultures with the Ro elicitor resulted in a more rapid initial accumulation of this end product when compared with GSH, however, sativan (the 2–methoxy ester of vestitol) previously reported to co-accumulate in Lotus leaves was only detected following elicitation with high concentrations of GSH. Ro and GSH elicitors also induced the accumulation of a number of other phenylpropanoid compounds putatively identified as chalcones. The addition of thiol and carbohydrate elicitors to Lotus root cultures also resulted in characteristic changes in root morphology. Glutathione, in particular, resulted in the inhibition of root growth due to differential damage of meristem cells.