Thigmomorphogenesis inBryonia dioica: Changes in soluble and wall peroxidases,phenylalanine ammonia-lyase activity,cellulose, lignin content and monomeric constituents

Rubbing young internodes ofBryonia dioica results in a reduced elongation and an increased diameter of the internodes. In the present study activities of some enzymes involved in the lignification process and levels of lignification were compared in rubbed and non-rubbed internodes. Rubbing caused an increase in the activities of phenylalanine ammonia-lyase and soluble and ionically- and covalently-bound cell wall peroxidases. Sensitivity of the covalently-bound wall peroxidase assay was markedly increased if syringaldazine was used as a substrate. Mechanical perturbation induced an increase in lignin, lignin monomer (sinapylic, coniferylic and p-coumarylic alcohols) content and the number of lignifying vessels. Conversely, rubbing resulted in a decrease in cellulose content. The hypothetical interpretation of the thigmomorphogenetic response through cell wall lignification and hence rigidification is consistent with all the presented results. A comparison is possible between this accelerated lignification and induced lignification as a mechanism of disease resistance. the thigmomorphogenetic response inBryonia dioica can be considered as a mechanism of resistance in order to withstand further environmental mechanical perturbation.Research partly supported by the Belgian FRFC grant 2.9009 to T.G. and by the French CNRS (LA 45, RCP 474).