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Abstract. Rubbing young internodes of Eryonia 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 walJ 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 lignifrcation 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 in Bryonia dioica can be considered as a mechanism of resistance in order to withstand further environmental mechanical perturbation.

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Rubbing‐induced inhibition of elongation in Bryonia dioica was completely prevented by 10−7M cobalt chloride. Cellular redistribution of peroxidases, mainly characterized by transiently enhanced membrane‐binding of soluble peroxidases, occurred as an immediate consequence of rubbing and was not inhibited by Co2+. Ethylene synthesis and 1‐aminocyclopropane‐1‐carboxylic acid (ACC) conversion readily increased upon rubbing and fell soon afterwards, but ACC conversion then increased again progressively. Co2+ did not drastically counteract these changes, except for the second rise in ACC conversion which was completely eliminated. The rubbing‐induced rise in ethyiene production and ACC conversion was closely correlated to microsomal ACC conversion and peroxidase activity, but only during the first hours after rubbing. The presented approach enables us to correlate stress‐induced ethylene production to membrane‐binding of peroxidases. It is suggested that ACC conversion in Bryonia dioica is triggered by two different, sequentially ordered mechanisms. The difference in the effects of Co2+ on elongation and ethylene production is discussed with respect to the role of ethylene in thigmomorphogensis.

Calli have been initiated in vitro from young internodes (control and rubbed) of Bryonia dioica, where previously it had been shown, using intact plants, that rubbing induced limited growth through enhanced lignification. Calli derived from rubbed internodes were somewhat more compact and showed biochemical changes, i.e. enhanced activity of total peroxidase and isoperoxidases, enhanced production of l-aminocyclopropane-l-carboxylic acid (ACC) and ethylene, enhanced tissue capacity to convert ACC into ethylene, enhanced activity of phenylalanine ammonia-lyase (PAL) and higher content of lignin, which characterized rubbed internodes. Differences in ethylene metabolism between the two types of calli tended to fade from the third week onwards of initial culture, whereas lignin content, peroxidase activity and peroxidase isoenzyme pattern appeared to be more persistant rubbinginduced markers for several subcultures. The results point to the persistance of environmentally induced changes in gene expression.