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 response was measured by an increase, as compared to controls, in Ca2+, Mg2+ and K+ concentrations in the exudate from the stump of stems excised at the first leaf (maize) or cotyledonary node at various times after pinching. The enhanced apoplastic cation concentrations were shown to be transient, diminishing with time. Usually no response could be measured if excision was delayed more than 3 min. The number of pinches affected the magnitude of the response, with one pinch sufficient in most cases. Our data suggest that transient changes in extracellular cations are involved in signal transduction or as a second messenger in response to perturbations.