N-ACYLPHOSPHATIDYLETHANOLAMINE IN DRY AND IMBIBING COTTONSEEDS - AMOUNTS, MOLECULAR-SPECIES, AND ENZYMATIC-SYNTHESIS

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 hirsu tom 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 a nd 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 in creased such that the relative percentage of NAPE was similar in dry a nd soaked seeds (2.3 mol% compared to 2.6 mol%, respectively). The maj or molecular species of NAPE were identified in both dry and soaked se eds by fast atom bombardment mass spectrometry and collisionally activ ated dissociation tandem mass spectrometry as 16:0/1 8:2-PE(N-palmitoy l), 16:0/1 8:2-PE(N-linoleoyl), and 18:2/18:2-PE(N-palmitoyl). The spe cific activity of NAPE synthase in seed extracts increased with increa sing 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, o ur results indicate that NAPE is present in dry cottonseeds and synthe sized during imbibition. The biosynthesis of NAPE provides a mechanism for maintaining membrane integrity during seed rehydration and may in dicate that NAPE plays a protective role in intracellular membranes of plant tissues, as has been suggested for intracellular membranes of a nimal tissues.