Thigmomorphogenesis in Solanum lycopersicum: morphological and biochemical responses in stem after mechanical stimulation

Solanum lycopersicum Mill. growth responses to mechanical stimulation showed that rubbing applied to the fourth tomato internode inhibit elongation.This morphological change was correlated with an enhancement in lignification process. Stress lignins synthesized in response to this mechanical elicitation displayed a distinct structure, relative to constitutive lignins. They were found substantially enriched in syringyl (S) units. Peroxidase (EC 1.1.1.7) activity investigated in the rubbed internode was induced 24 h after stress application. In order to get more information about peroxidase implication in growth restriction observed in internode 4, protein isoform purification was performed using concanavalin and cation exchange chromatography. The Western blot analysis of the purified protein extract from rubbed internode revealed the appearance of a novel basic peroxidase isoform. Moreover, an increase in the basic isoform activity was observed in rubbed internode as compared with the control one. Increased activities of cinnamyl alcohol dehydrogenase (CAD) (EC 1.1.1.197) and of peroxidase (EC 1.1.1.7), enzymes designated as markers of lignification process were associated with a higher lignin content in the rubbed internode. Cell wall rigidification as a result of changes in enzyme activities and accelerated lignification could explain the reduced elongation of treated tomato internodes