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 transient increase of cytoplasmic free calcium concentration ([Ca2+]c) in cells from Lycopersicon esculentum mesophyll. The systemin-induced Ca2+ increase was slightly but not significantly reduced by L-type Ca2+ channel blockers (nifedipine, verapamil and diltiazem) and the Ca2+ chelator [ethylene glycol tetraacetic acid (EGTA)], whereas inorganic Ca2+ channel blockers (LaCl3, CdCl2 and GdCl3) and compounds affecting the release of intracellular Ca2+ from the vacuole (ruthenium red, LiCl, neomycin) strongly reduced the systemin-induced [Ca2+]c increase. By contrast, no inhibitory effect was seen 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 increase of cytoplasmic Ca2+. The systemin-induced elevation of cytoplasmic Ca2+ which might be an early step in the systemin signalling pathway, appears to involve an influx of extracellular Ca2+ simultaneously through several types of Ca2+ permeable channels, and a release of Ca2+ from intracellular stores sensitive to blockers of inositol 1,4,5-triphosphate (IP3)- and cyclic adenasine 5’-diphosphoribose (cADPR)-mediated Ca2+ release.