Systemin triggers an increase of cytoplasmic calcium in tomato mesophyll cells: Ca2+ mobilization from intra- and extracellular compartments

We show here that, within 1-2 min of application, systemin triggers a trans ient increase of cytoplasmic free calcium concentration ([Ca2+](c)) in cell s from Lycopersicon esculentum mesophyll. The systemin-induced Ca2+ increas e was slightly but not significantly reduced by L-type Ca2+ channel blocker s (nifedipine, verapamil and diltiazem) and the Ca2+ chelator [ethylene gly col tetraacetic acid (EGTA)], whereas inorganic Ca2+ channel blockers (LaCl 3, CdCl2 and GdCl3) and compounds affecting the release of intracellular Ca 2+ from the vacuole (ruthenium red, LiCl, neomycin) strongly reduced the sy stemin-induced [Ca2+](c) increase. By contrast, no inhibitory effect was se en with the potassium and chloride channel blockers tested. Unlike systemin , other inducers of proteinase inhibitor (PI) and of wound-induced protein synthesis, such as jasmonic acid (JA) and bestatin, did not trigger an incr ease of cytoplasmic Ca2+. The systemin-induced elevation of cytoplasmic Ca2 + which might be an early step in the systemin signalling pathway appears t o involve an influx of extracellular Ca2+ simultaneously through several ty pes of Ca2+ permeable channels, and a release of Ca2+ from intracellular st ores sensitive to blockers of inositol 1,4,fi-triphosphate (IP3)- and cycli c adenasine 5'-diphosphoribose (cADPR)-mediated Ca2+ release.