Aluminum inhibits phosphatidic acid formation by blocking the phospholipase C pathway

Aluminum (Al(3+)) 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 Al(3+) using Coffea arabica suspension cells. We pre-labeled cells with [(32)P]orthophosphate ((32)Pi) and assayed for (32)P-PA formation in response to Al(3+). Treating cells for 15 min with either AlCl(3) or Al(NO(3))(3) inhibited the formation of PA. In order to test how Al(3+) affected PA signaling, we used the peptide mastoparan-7 (mas-7), which is known as a very potent stimulator of PA formation. The Al(3+) inhibited mas-7 induction of PA response, both before and after Al(3+) 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 AlCl(3) suggesting the involvement of the PLC/DGK pathway. Incubation of cells with PLC inhibitor, U73122, affected PA formation, like AlCl(3) did. PLD in vivo activation by mas-7 was reduced by Al(3+). 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.