Intracellular Localization of N-Acylphosphatidylethanolamine Synthesis in Cotyledons of Cotton (Gossypium hirsutm L.) Seedlings

Abstract

iV-Acylphosphatidylethanolamine (NAPE) is synthesized from free fatty acids and phosphatidylethanolamine (PE) by a membrane-bound acyltransferase enzyme designated NAPE synthase. Here we report the subcellular location of NAPE synthase in cotyledons of germinated cotton seedlings. Organelle marker enzyme assays and transmission electron microscopy were used to evaluate cellular fractions separated by differential centrifugation, sucrosedensity gradient centrifugation, and aqueous two-phase partitioning. NAPE synthase was associated with fractions enriched in ER, Golgi and plasma membranes. NAPE synthase was not located in mitochondria, plastids, peroxisomes, or cytosol. Consistent with these observations, NAPE synthase also was localized in membranes of the secretory pathway in spinach leaves. Because PE is synthesized primarily in the ER, these results suggest that JV-acylation of PE may be a lipid modification of the compartments of the secretory pathway providing a mechanism for supplying NAPE to the plasma membrane. These data are particularly relevant given the recent findings that NAPE biosynthesis is increased in elicitor-treated plant cells [Chapman et al. (1995) Physiol. Plant. 95: 120].