N-Acylphosphatidylethanolamine in Dry and Imbibing Cottonseeds (Amounts, Molecular Species, and Enzymatic Synthesis)

Abstract

KAcylphosphatidylethanolamine (NAPE), an unusual acylated derivative of phosphatidylethanolamine (PE), was recently shown to be synthesized from PE and free fatty acids i n 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 i n 4-h-soaked seeds. Total phospholipid/seed also increased such that the relative percentage of NAPE was similar i n 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(Kpalmitoyl), 16:0/18:2-PE(N-linoleoyl), and 18:2/18:2-PE(Kpalmitoyl). l h e specific activity of NAPE synthase in seed extracts increased with increasing time of imbibition from 35 pmol h-' mg-' protein in dry seeds to 129 pmol h-' mg-' protein i n 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 i n intracellular membranes of plant tissues, as has been suggested for intracellular membranes of animal tissues.NAPE, which was first identified as a minor constituent of wheat flour (Bomstein, 1965), has recently become recognized as a widespread, albeit minor, phospholipid component in intracellular membranes of plants (Chapman and

N-Acylphosphatidylethanolamine Accumulation in Potato Cells upon Energy Shortage Caused by Anoxia or Respiratory Inhibitors

“…All NAPE molecules belonging to group III (Table I) obviously are N-acylated with 18 carbon fatty acids. These results present two striking differences with those reported by Sandoval et al (1995). First, osmotic stress did not induce the synthesis of new NAPE species upon imbibition of cottonseeds, but only increased the level of preexisting species peaking at m/z 952 and 976 and corresponding to our subgroups I-b and II-c. Second, imbibed cottonseeds were poor in 18/18/18-NAPE species (Sandoval et al, 1995) whereas these species represent one of the major NAPE groups in both normoxic and anoxic potato cells (group III, Table I).…”

“…When cells are submitted to stress treatments able to induce NAPE synthesis under prelytic conditions, they can do it because there are still enough fatty acids available in the basal FFA pool to N-acylate additional PE molecules. At this stage, cells are stressed but alive and the extra NAPE species synthesized under these conditions may play active roles as precursors for signal molecules (Chapman et al, 1995aTripathy et al, 1999) and as membrane protectants (Sandoval et al, 1995;Chapman and Sprinkle, 1996). These properties were apparently not required when the energetic competence of potato cells was progressively decreased because no net NAPE formation could be evidenced during the prelytic phase of the anoxic treatment (Fig.…”

“…3; Table II) or treated with NaN 3 plus SHAM under air (Table III). To date, stress-induced stimulations of plant NAPE synthesis have been observed after seed imbibition (Sandoval et al, 1995), after elicitor treatment of tobacco cells (Chapman et al, 1995a) and after chilling or abscisic acid treatment of cotton seedlings (Chapman and Sprinkle, 1996). Our results show that anoxic stress leads to a similar effect, although the increase in NAPE level is not due to the absence of O 2 per se (Table III), but to the very unfavorable energetic status that prevails when respiration is either impossible or simply blocked by appropriate inhibitors under normoxic conditions .…”

“…In rehydrating cotton (Gossypium hirsutum) seeds, NAPE was suggested to act as a membraneprotecting and -stabilizing compound (Sandoval et al, 1995). The involvement of NAPE in elicitorinduced signaling in tobacco (Nicotiana tabacum) cells (Chapman et al, 1995a and leaves (Tripathy et al, 1999) was suggested from the modulation by N-acylethanolamine of short-term (e.g.…”

N-Acylethanolamines Are Metabolized by Lipoxygenase and Amidohydrolase in Competing Pathways during Cottonseed Imbibition

“…9). In fact, NAPE biosynthesis was shown to be increased during seed imbibition, germination, and early postgerminative growth (Sandoval et al, 1995;Chapman and Sprinkle, 1996) as judged by increases in lipid levels and enzyme activity.…”