Ritchie and Gilroy developed an in vitro system to test whether abscisic acid (ABA) activates phospholipase D (PLD) in cereal aleurone cells through a heterotrimeric G protein (G protein). Stimulation of PLD activity by ABA was inhibited by GDP-β-S and enhanced by GTP-γ-S, consistent with the involvement of a G protein. Further support for a G protein came from the experiments performed in the presence of pertussis toxin, which inhibited ABA-stimulated PLD activity in vitro and in vivo. Membrane fractionation studies suggest that the ABA signaling pathway and the ABA-regulated PLD is associated with the plasma membrane. Thus, on the basis of results from this in vitro system, ABA activates a plasma membrane receptor that couples to a G protein, which leads to the regulation of a plasma membrane-localized PLD.
Ritchie, S., and Gilroy, S. (2000) Abscisic acid stimulation of phospholipase D in the barley aleurone is G-protein-mediated and localized to the plasma membrane. Plant Physiol. 124: 693-702. [Abstract] [Full Text]