Calcium requirement for the secretion of peroxidases by plant cell suspensions.

Spinach (Spinacia oleracea, L.) cells in liquid culture release peroxidases. This release is reduced by EGTA and promoted by calcium ions. In a medium deprived of calcium the rate of peroxidase release is low, but immediately after addition of I mM calcium there is a sudden increase of the extracellular peroxidase activity. Extracellular calcium apparently penetrates into the cultured cells rather freely and, as a consequence, the rate of peroxidase secretion by these cells is directly correlated with the concentration of calcium in the medium. Magnesium, at twice the concentration used for calcium, has no effect on the release of peroxidases. Cells treated with Na azide, Na hydrogenarsenate of fluphenazine secrete less peroxidase upon addition of calcium.