N-acylphosphatidylethanolamine in dry and imbibing cottonseeds. Amounts, molecular species, and enzymatic synthesis.

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N-Acylphosphatidylethanolamine (NAPE), an unusual acylated derivative of phosphatidylethanolamine (PE), was recently shown to be synthesized from PE and free fatty acids in cotyledons of cotton (Gossypium hirsutum L.) seedlings (K.D. Chapman, T.S. Moore [1993] Plant Physiol 102: 761-769). Here we report that NAPE is present in dry seeds of cotton and increases with time of imbibition from 2.31 nmol/seed in dry seeds to 4.26 nmol/seed in 4-h-soaked seeds. Total phospholipid/seed also increased such that the relative percentage of NAPE was similar in dry and soaked seeds (2.3 mol% compared to 2.6 mol%, respectively). The major molecular species of NAPE were identified in both dry and soaked seeds by fast atom bombardment mass spectrometry and collisionally activated dissociation tandem mass spectrometry as 16:0/18:2-PE(N-palmitoyl), 16:0/18:2-PE(N-linoleoyl), and 18:2/18:2-PE(N-palmitoyl). The specific activity of NAPE synthase in seed extracts increased with increasing time of imbibition from 35 pmol h-1 mg-1 protein in dry seeds to 129 pmol h-1 mg-1 protein in 4-h-soaked seeds. Collectively, our results indicate that NAPE is present in dry cottonseeds and synthesized during imbibition. The biosynthesis of NAPE provides a mechanism for maintaining membrane integrity during seed rehydration and may indicate that NAPE plays a protective role in intracellular membranes of plant tissues, as has been suggested for intracellular membranes of animal tissues.