Calcium-dependent proteinase activity in root cultures of Arabidopsis.

The presence of calcium-dependent proteinase in plants was investigated using soluble proteins from Arabidopsis root cultures. Calcium increased the proteolytic activity by two to three fold. Calcium-stimulated proteolytic activity was inhibited by different protease inhibitors. The highest inhibition (79%) of calcium-dependent proteolytic activity was observed in the presence of leupeptin. Thirty-eight percent of calcium-dependent proteolytic activity was inhibited by E-64, an inhibitor of cysteine proteinases. Calmodulin did not have any effect on calcium-dependent as well as calcium-independent proteolytic activity in the cellular extract. These results provide the first evidence for the presence of calcium activated proteinase in plants and open new avenues to investigate the mode of calcium action in plants.