Cation signals rapidly elicited in several different plant species by pinching the leaves

Several plant species (snapbeans, soybeans, tomatoes, and maize)were shown to respond within 3–60 s to pinching a single,fully expanded leaf with a clinical haemostat. The responsewas measured by an increase, as compared to controls, in Ca²⁺, Mg²⁺ and K⁺ concentrations in the exudate from the stump ofstems excised at the first leaf (maize) or cotyledonary nodeat various times after pinching. The enhanced apoplastic cationconcentrations were shown to be transient, diminishing withtime. Usually no response could be measured if excision wasdelayed more than 3 min. The number of pinches affected themagnitude of the response, with one pinch sufficient in mostcases. Our data suggest that transient changes in extracellularcations are involved in signal trans-duction or as a secondmessenger in response to perturbations. Key words: Cations, signalling, Ca²⁺, Mg²⁺, K⁺