Increased <i>N</i>‐acylphosphatidylethanolamine biosynthesis in elicitor‐treated tobacco cells

Abstract

Previous studies with tobacco ( Nicotiana tabacum L.) cell suspensions indicated that elicitation of defense response (production of phytoalexins) with xylanase (1,4‐β‐D‐xylanxylanohydrolase: EC 3.2.1.8) resulted in a dramatic acylation of phytosterols (Moreau et al. 1994). N ‐acylphosphatidylethanolamine (NAPE), an acylated derivative of phosphatidylethanolamine (PE), was recently demonstrated to be synthesized in vivo in plant tissues (Chapman and Moore 1993a). Here we report that acylation of PE was increased in elicitor‐treated cells. NAPE levels increased 3‐fold (from 1.6 to 4.8 mol% of total phospholipids) after a 2‐h treatment of cell suspensions with xylanase (1 δg ml −1 ). Specific activity of NAPE synthase increased in parallel with NAPE levels. Levels of NAPE and NAPE synthase activity declined during the period of 2–4 h after elicitation while levels of acylated sterolglycosides (ASG) continued to increase. Radiolabeling studies with [2 −14 C]‐ethanolamine confirmed that three times as much NAPE was synthesized in elicitor‐treated cells compared to that in unelicited cells. Patterns of incorporation of [1‐ 14 C]‐palmitic acid into membrane phospholipids in elicitor‐treated cells suggested that increased acylation of lipids may be a result of changes in the acyl‐coenzyme A pool. Treatment of cells with purified ethylene biosynthesis‐inducing xylanase (EIX; 1 δg ml −1 cells) resulted in increased levels of NAPE synthase activity comparable to those observed with the commercial preparations of xylanase. Boiled xylanase did not elicit an increase in the specific activity of NAPE synthase. Collectively our results demonstrate that the accumulation of NAPE in tobacco cells is attributable to increased activity of NAPE synthase. This suggests that NAPE may be specifically synthesized to play a protective role in membranes of plant cells as has been suggested for membranes of damaged animal cells.