Mastoparan analogues stimulate phospholipase C- and phospholipase D-activity in Chlamydomonas:: a comparative study

The G-protein activator mastoparan and its analogues are becoming popular tools for studying signalling in plants. Therefore the abilities of mastoparan, mas7, mas8, and mas17 to activate phospholipase C (PLC), PLD and to induce the deflagellation response in Chlamydomonas moewusii Gerloff were compared. The aim was to test whether their relative potencies in a plant system resemble those reported for bovine brain G(o) and G(i), as is generally assumed, and to determine at which concentrations cells become permeabilized, a known effect of higher concentrations. The concentrations at which 50% deflagellation was induced, were 2.0 mu M mastoparan, 3.0 mu M mas8, 3.6 mu M mas7, and 5.8 mu M mas17, Similar activities were found for the production of phosphatidic acid, which is the result of the combined activities of PLD and PLC (together with diacylglycerol kinase), PLD activity alone was measured in vivo by its ability to phosphatidylate n-butanol, Surprisingly, the concentrations that stimulated maximum activity were about 10-fold lower (similar to 1 mu M) than those that stimulated maximum PLC activity (similar to 10 mu M). Mas17 was an exception with both maxima above 10 mu M. All the compounds except mas17 permeabilized C, moewusii cells. The concentrations at which 50% of the cells were permeabilized to Even's blue were 7.4 mu M mas8, 16.0 mu M mas7 and 22.4 mu M mastoparan. In conclusion, only mastoparan itself and the least active analogue mas17 induced maximum deflagellation, PLC and PLD activities without permeabilizing the cells.