N-acylethanolamines in signal transduction of elicitor perception. Attenuation of alkalinization response and activation of defense gene expression

In a recent study of N-acylphosphatidylethanolamine (NAPE) metabolism in el icitor-treated tobacco (Nicotiana tabacum L.) cells, we identified a rapid release and accumulation of medium-chain N-acylethanolamines (NAEs) (e.g. N -myristoylethanolamine or NAE 14:0) and a compensatory decrease in cellular NAPE (K.D. Chapman, S. Tripathy, B. Venables, A.D. Desouza [1998] Plant Ph ysiol 116: 1163-1168). In the present study, we extend this observation and report a 10- to 50-fold increase in NAE 14:0 content in leaves of tobacco (cv Xanthi) plants treated with xylanase or cryptogein elicitors. Exogenous ly supplied synthetic NAE species affected characteristic elicitor-induced and short- and long-term defense responses in cell suspensions of tobacco a nd long-term defense responses in leaves of intact tobacco plants. In gener al, synthetic NAEs inhibited elicitor-induced medium alkalinization by toba cco cells in a time- and concentration-dependent manner. Exogenous NAE 14:0 induced expression of phenylalanine ammonia lyase in a manner similar to f ungal elicitors in both cell suspensions and leaves of tobacco. NAE 14:0, b ut not myristic acid, activated phenylalanine ammonia lyase expression at s ubmicromolar concentrations, well within the range of NAE 14:0 levels measu red in elicitor-treated plants. Collectively, these results suggest that NA PE metabolism, specifically, the accumulation of NAE 14:0, are part of a si gnal transduction pathway that modulates cellular defense responses followi ng the perception of fungal elicitors.