Comparison of glycerolipid content of elongating (8-10 dpa) and maturing (21 dpa) fiber cells (from cv Coker 312) determined by ESI-MS/MS. Lipids are quantified on nmol mg-1 dry weight basis. Lipid quantities were calculated based on internal standards included for each class (see methods) and the amount for each class represents the sum of individual molecular species for that class. Bars represent the means and SD of five independent extractions.
Abbreviations:
DGDG: digalactosyldiacylglycerol,
MGDG: monogalactosyldiacylglycerol
PG: phosphatidylgycerol
LPG: lyso-phosphatidylglycerol
LPC: lyso-phosphatidylcholine
LPE: lyso-phosphatidylethanolamine
PC:
phosphatidylcholine
PE: phosphatidylethanolamine
PI: phosphatidylinositol
PS: phosphatidylserine
PA: phosphatidic acid
Individual molecular species profiles quantified by ESI-MS/MS for phosphatidylcholine in extracts from elongating (8-10 dpa) and maturing (21 dpa) fiber cells. Fiber samples were from cv Coker 312 plants tagged at anthesis, and lipids were extracted immediately upon excision of ovules from bolls. Numerical designations represent total number of acyl carbons: total numbers of double bonds. Data for each molecular species represent the means and SD of five independent extractions and are presented as mol% of total glycerolipid.
Summary scheme for the cellular compartmentation and proposed pathway leading to the synthesis of PC 34:3 (16:0, 18:3), a major glycerolipid molecular species in both elongating and maturing fiber cells. The diagram is based on both metabolite profiles and EST occurrences (numbers in parentheses) for enzymes in these pathways, and is consistent with the synthetic pathways described for extraplastidial PC in other types of plant cells. The fatty acids are assembled de novo in the plastids of fiber cells and exported to the endoplasmic reticulum (ER) for glycerolipid assembly and subsequent modification (e.g. introduction of additional double bonds). The acylglycerol base for other phospholipids, such as PE and PI, can be synthesized using the same machinery. Numerical designations for fatty acids represent total number of acyl carbons: total numbers of double bonds.
