Emerging physiological roles for N-acylphosphatidylethanolamine metabolismin plants: signal transduction and membrane protection

The activation of N-acylphosphatidylethanolamine (NAPE) metabolism in plant s appears to be associated mostly with cellular stresses. In response to pa thogen elicitors, NAPE is hydrolzyed by phospholipase-D (PLD), and correspo nding medium-chain, saturated N-acylethanolamines (NAEs) are released by pl ant cells where they act as lipid mediators to modulate ion flux and activa te defense gene expression. In desiccated seeds of higher plants, long-chai n, saturated and unsaturated NAEs are prevalent, but are rapidly metabolize d during the first few hours of imbibition, a period of substantial osmotic stress. NAPE synthesis is increased in seeds during this same period of ra pid rehydration. A membrane-bound enzyme designated NAPE synthase has been purified from imbibed cottonseeds and its unusual biochemical properties su ggest that it may scavenge free fatty acids in vivo. This feature of NAPE m etabolism may be unique to higher plants a may be a mechanism for the rapid recycling of fatty acids back into membrane-associated NAPE. Altogether, i ncreasing evidence indicates that NAPE metabolism in plants shares function al similarities with NAPE metabolism in animal systems, including signal tr ansduction and cellular protection. In particular, the emerging role of rel eased NAEs as lipid mediators in plant defense signaling represents an intr iguing parallel to 'endocannabinoid signaling' in several mammalian cell ty pes. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.