CATION SIGNALS RAPIDLY ELICITED IN SEVERAL DIFFERENT PLANT-SPECIES BYPINCHING THE LEAVES

Several plant species (snapbeans, soybeans, tomatoes, and maize) were shown to respond within 3-60 s to pinching a single, fully expanded le af 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 c otyledonary node at various times after pinching. The enhanced apoplas tic cation concentrations were shown to be transient, diminishing with time. Usually no response could be measured if excision was delayed m ore than 3 min. The number of pinches affected the magnitude of the re sponse, with one pinch sufficient in most cases. Our data suggest that transient changes in extracellular cations are involved in signal tra nsduction or as a second messenger in response to perturbations.