Plant stress adaptation often uses changes in cytosolic Ca2+ to bring about responses via changing the activity of Ca2+-sensor proteins including Ca2+-dependent protein kinases (CDPK). The activity of a tobacco CDPK(s) is essential for elicitation of the hypersensitive reaction, a typical plant defence response. Moreover, it is becoming apparent that CDPKs might also facilitate cross-talk between different Ca2+-mediated stress signalling pathways.