Phospholipase activities associated with the tonoplast from Acer pseudoplatanus cells: identification of a phospholipase A1 activity.

The study of phospholipase activities associated with the tonoplast of Acer pseudoplatanus was performed in vitro with sn-2-[14C]acylphosphatidylcholine (PC) as a substrate. The hydrolysis of radiolabelled PC into [14C]phosphatidic acid and [14C]lyso-PC demonstrated the presence of phospholipase D and A1 activities, respectively, associated with the tonoplast of Acer pseudoplatanus. The vacuolar sap did not show any significant phospholipase activity. In a second step, the properties of the phospholipase A1 activity was studied using tonoplast endogenous PC labelled in vivo with [14C]choline as a substrate. The phospholipase A1 showed an optimal activity at pH about 6-6.5, did not necessarily require divalent cations, but was stimulated by Mg2+ and particularly by Ca2+. This work presents the first evidence for the presence of phospholipases A1 in plant cells.