Activation of phospholipase D by calmodulin antagonists and mastoparan in carnation petals

An in vivo assay for phospholipase D (PLD; EC 3.1.4.4) activity, based on its transphosphatidylation property, is described in detail and was used to study putative post-translational regulation mechanisms of PLD activity in carnation [Dianthus caryophyllus L.) petals. A variety of agents was applied to petal discs. The calmodulin (CaM) antagonists propranolol, /V-(6-aminohexyl)-5-chloro-1 -naphthalenesulphonamide (W7) and N-(6-aminohexyl)-1 -naphthalenesulphonamide (W5), stimulated PLD activity in a dose-dependent manner. EGTA partially inhibited the stimulation by the CaM antagonists. Erythrosin B, an inhibitor of CaMdependent P-type Ca + -ATPases, slightly stimulated PLD activity. The results suggest that part of the stimulation of PLD activity by CaM antagonists is due to an increased intracellular Ca + -concentration. PLD activity was stimulated by mastoparan in a doseand timedependent manner. The signal-like activation kinetics suggests that mastoparan activates PLD (in)directly via