Calcium (Ca(2+) ) signals regulate many aspects of plant development, including a programmed cell death pathway that protects plants from pathogens (hypersensitive response) . A double knockout mutation of the vacuolar Ca(2+) pumps ACA4 (AT2G41560) and ACA11 (AT3G57330) in Arabidopsis (Arabidopsis thaliana) results in a high frequency of hypersensitive response-like lesions.
