Inhibition of Phospholipase Dα byN-Acylethanolamines

Abstract

Abstract N-Acylethanolamines (NAEs) are endogenous lipids in plants produced from the phospholipid precursor,N-acylphosphatidylethanolamine, by phospholipase D (PLD). Here, we show that seven types of plant NAEs differing in acyl chain length and degree of unsaturation were potent inhibitors of the well-characterized, plant-specific isoform of PLD—PLDα. It is notable that PLDα, unlike other PLD isoforms, has been shown not to catalyze the formation of NAEs fromN-acylphosphatidylethanolamine. In general, inhibition of PLDα activity by NAEs increased with decreasing acyl chain length and decreasing degree of unsaturation, such thatN-lauroylethanolamine andN-myristoylethanolamine were most potent with IC50s at submicromolar concentrations for the recombinant castor bean (Ricinus communis) PLDα expressed inEscherichia coli and for partially purified cabbage (Brassica oleracea) PLDα. NAEs did not inhibit PLD from Streptomyces chromofuscus, and exhibited only moderate, mixed effects for two other recombinant plant PLD isoforms. Consistent with the inhibitory biochemical effects on PLDα in vitro,N-lauroylethanolamine, but not lauric acid, selectively inhibited abscisic acid-induced closure of stomata in epidermal peels of tobacco (Nicotiana tabacum cv Xanthi) andCommelina communis at low micromolar concentrations. Together, these results provide a new class of biochemical inhibitors to assist in the evaluation of PLDα physiological function(s), and they suggest a novel, lipid mediator role for endogenously produced NAEs in plant cells.