A cDNA clone (Bc329) encoding calmodulin was isolated from a Bryonia cDNA library by screening with cloned Arabidopsis calmodulin cDNA. The cDNA Bc329 was 899 bp full-length clone. The predicted amino acid sequence consists of 149 residues and reveals a high homology with other known plant calmodulins (91 to 99% identity). Genomic southern blot suggests that Bryonia calmodulin is encoded by a single-copy gene. The Bc329 clone was used as a probe to study the expression of calmodulin mRNA after a mechanical stimulus applied on young Bryonia internodes. The steady-state of calmodulin mRNA reached a maximum 30 min after the treatment before it progressively decreased. The role of calcium and calmodulin as second messengers is discussed with regard to environmental changes.