Aluminum inhibits phosphatidic acid formation by blocking the phospholipase C pathway

Aluminum (Al3+) has been recognized as a main toxic factor in crop production in acid lands. Phosphatidic acid (PA) is emerging as an important lipid signaling molecule and has been implicated in various stress-signaling pathways in plants. In this paper, we focus on how PA generation is affected by Al3+ using Coffea arabica suspension cells. We pre-labeled cells with [P-32] orthophosphate ((32)Pi) and assayed for P-32-PA formation in response to Al3+. Treating cells for 15 min with either AlCl3 or Al(NO3)(3) inhibited the formation of PA. In order to test how Al3+ affected PA signaling, we used the peptide mastoparan-7 (mas-7), which is known as a very potent stimulator of PA formation. The Al3+ inhibited mas-7 induction of PA response, both before and after Al3+ incubation. The PA involved in signaling is generated by two distinct phospholipid signaling pathways, via phospholipase D (PLD; EC: 3.1.4.4) or via Phospholipase C (PLC; EC: 3.1.4.3), and diacylglycerol kinase ( DGK; EC 2.7.1.107). By labeling with (32)Pi for short periods of time, we found that PA formation was inhibited almost 30% when the cells were incubated with AlCl3 suggesting the involvement of the PLC/DGK pathway. Incubation of cells with PLC inhibitor, U73122, affected PA formation, like AlCl3 did. PLD in vivo activation by mas-7 was reduced by Al3+. These results suggest that PA formation was prevented through the inhibition of the PLC activity, and it provides the first evidence for the role of Al toxicity on PA production.