Inhibition of internode growth due to mechanical stress in Bryonia dioica: relationship between changes in DNA methylation and ethylene metabolism

Abstract
Changes in the level of cytosine methylation were assessed by HPLC in mechanically stressed Bryonia dioica. Rubbing young internodes. which results in growth inhibition and ethylene production, induced a rapid and transient decrease of cytosine methylation in DNA. The level of cytosine methylation was about 25% in young internodes and dropped to nearly 0% in less than 1 h before increasing to the normal level within 3 h. A decreasing gradient of DNA methylation occurred naturally along the plant, from the apex to the base. The pool of S‐adenosylmethionine was also measured in order to establish a possible relationship between ethylene metabolism and DNA methylation. The role of DNA methylation in gene regulation is discussed and different mechanisms for methylation are considered.