Thigmomorphogenesis: Evidence for a translocatable thigmomorphogenetic factor induced by mechanical perturbation of beans (Phaseolus vulgaris)

Mechanical perturbation of bean (Phaseolus vulgaris L.) internodes results in reduced elongation and increased diameter of the internodes (thigmomorphogenesis). Perturbation of a single lower internode results in thigmorphogenesis in that internode and all of those internodes above it, the degree of which depends on the age (size) of the internodes and the frequency of perturbation. Application of ethephon to the internodes mimics mechanical perturbation. Early removal of the shoot tip or the cotyledons does not effect thigmomorphogenesis, indicating that those organs do not exert control over the response. Mechanical perturbation of one plant of a pair grafted together at the first internodes results in thigmomorphogenesis in both plants. This indicates the transport of some factor from the mechanically perturbed donor to the non-treated receiver. Evidence is presented to support the contention that ethylene is not this transportable factor.