Elicitor-activated phospholipase A2 generates lysophosphatidylcholines that mobilize the vacuolar H+ pool for pH signaling via the activation of Na+-dependent proton fluxes

Abstract

The elicitation of phytoalexin biosynthesis in cultured cells of California poppy involves a shift of cytoplasmic pH via the transient efflux of vacuolar protons. Intracellular effectors of vacuolar proton transport were identified by a novel in situ approach based on the selective permeabilization of the plasma membrane for molecules of ≤10 kD. Subsequent fluorescence imaging of the vacuolar pH correctly reported experimental changes of activity of the tonoplast proton transporters. Lysophosphatidylcholine (LPC) caused a transient increase of the vacuolar pH by increasing the Na+ sensitivity of a Na+-dependent proton efflux that was inhibited by amiloride. In intact cells, yeast elicitor activated phospholipase A2, as demonstrated by the formation of LPC from fluorescent substrate analogs, and caused a transient increase of endogenous LPC, as determined by matrix-assisted laser desorption and ionization time-of-flight mass spectrometry. It is suggested that LPC generated by phospholipase A2 at the plasma membrane transduces the elicitor-triggered signal into the activation of a tonoplast H+/Na+ antiporter.