The Effects of Mastoparan on the Carrot Cell Plasma Membrane Polyphosphoinositide Phospholipase C

Abstract

When [3Hlinositol-labeled carrot (Daucus carota L.) cells were treated with 10 or 25 p~ wasp venom peptide mastoparan or the active analog Mas-7 there was a rapid loss of more than 70% of Plasma membranes isolated from mastoparan-treated cells had increased PIP-phospholipase C (PLC) activity. However, when Mas-7 was added to isolated plasma membranes from control cells, it had no effect on PIP-PLC activity at low concentrations and inhibited PIP-PLC at concentrations greater than 10 p~. In addition, guanosine-5'-0(3-thiotriphosphate) had no effect on the PIP-PLC activity when added to plasma membranes isolated from either the Mas-7-treated or control cells. The fact that Mas-7 did not stimulate PIP-PLC activity i n vitro indicated that the Mas-7-induced increase in PIP-PLC in vivo required a factor that was lost from the membrane during isolation.

Mastoparan-Induced Intracellular Ca2+ Fluxes May Regulate Cell-to-Cell Communication in Plants

“…The concentration of Mas-7 estimated in the injected cell (<1 p~) is the same as that which resulted in an increase in phosphatidylinositol-4-monophosphate biosynthesis in carrot cells (Cho et al, 1995), an increase in cell elongation in zucchini hypocotyls (Scherer, 1992), and calcium oscillations in acinar cells (Yule and Williams, 1991). The Ca'+ elevations obtained in staminal hairs were similar to Ca2+ changes reported for other systems; for example, 1 p~ Mas induced oscillations averaging 430 n M (Yule and Williams, 1991).…”

“…Mas and Mas-7 have been shown to cause an increase in [IP,] in severa1 plant systems (Quarmby et al, 1992;Legendre et al, 1993;Cho et al, 1995), and IP, has been reported to affect Ca2+ channels in plant vacuoles (Alexandre et al, 1990;Johannes et al, 1992;Allen and Sanders, 1994). Thus, we propose that Mas-7 stimulated IP, production in cell 1, which, in turn, caused Ca'+ release from Ir,-sensitive pools.…”

“…Tucker, unpublished results). To artificially initiate signaling, we used Mas, a cationic, amphiphilic tetradecapeptide that has been used as a tool to activate G protein (White et al, 1993;Armstrong and Blatt, 1995) and increase IP, and Ca2+ in algae and higher plants (Quarmby et al, 1992;Legendre et al, 1993;Drnbak and Watkins, 1994;Quarmby and Hartzell, 1994;Cho et al, 1995). We detected an increase in Ca2+ in the stimulated and neighboring cells, with a concomitant closure of plasmodesmata.…”

G Protein Activation Stimulates Phospholipase D Signaling in Plants.

“…Because mastoparan has been shown to activate PLC in this alga (Quarmby et al, 1992;Yueh and Crain, 1993;Quarmby and Hartzell, 1994;T. Munnik and A. Musgrave, unpublished results), soybean (Legendre et al, 1993), and carrot (Drgbak and Watkins, 1994;Cho et al, 1995), increasing the leve1 of DAG, which is rapidly phosphorylated to PtdOH, this result has been interpreted as the G protein activation of PLC. However, this interpretation does not account for the contribution that other G protein-activated effector enzymes can make to PtdOH production.…”

“…With the recent demonstrations that these artificial stimulators also activate PLC in plants Quarmby et al, 1992;Legendre et al, 1993;Dr0bak and Watkins, 1994;Cho et al, 1995), we tested their ability to activate PLD. Both were very effective, and PtdBut formation in C. eugametos increased approximately fivefold, whereas a similar increase in carnation petals was found after treatment with mastoparan.…”