Abstract
Previous work has demonstrated that plant leaf polar lipid fatty acid composition varies during the diurnal (dark–light) cycle. Fatty acid synthesis occurs primarily during the light, but fatty acid desaturation continues in the absence of light, resulting in polyunsaturated fatty acids reaching their highest levels toward the end of the dark period. In this work, Arabidopsis thaliana were grown at constant (21°C) temperature with 12-h light and 12-h dark periods. Collision induced dissociation time-of-flight mass spectrometry (MS) demonstrated that 16:3 and 18:3 fatty acid content in membrane lipids of leaves are higher at the end of the dark than at the end of the light period, while 16:1, 16:2, 18:0, and 18:1 content are higher at the end of the light period. Lipid profiling of membrane galactolipids, phospholipids, and lysophospholipids by electrospray ionization triple quadrupole MS indicated that the monogalactosyldiacylglycerol, phosphatidylglycerol, and phosphatidylcholine classes include molecular species whose levels are highest at end of the light period and others that are highest at the end of the dark period. The levels of phosphatidic acid (PA) and phosphatidylserine classes were higher at the end of the dark period, and molecular species within these classes either followed the class pattern or were not significantly changed in the diurnal cycle. Phospholipase D (PLD) is a family of enzymes that hydrolyzes phospholipids to produce PA. Analysis of several PLD mutant lines suggests that PLDζ2 and possibly PLDα1 may contribute to diurnal cycling of PA. The polar lipid compositional changes are considered in relation to recent data that demonstrate phosphatidylcholine acyl editing.
Highlights
The chloroplast is the single site of fatty acid synthesis in plants (Ohlrogge et al, 1979)
The collision induced dissociation (CID)–TOF mass spectrometry (MS) data confirm previous results showing that levels of 18:1 acyl chains in plant leaves are increased during the light period of the diurnal cycle and 18:3 levels are increased in the dark period (Browse et al, 1981; Ekman et al, 2007)
The CID–TOF MS data are generally in concert with data on apparent molecular species obtained by direct infusion electrospray ionization (ESI) triple quadrupole MS
Summary
The chloroplast is the single site of fatty acid synthesis in plants (Ohlrogge et al, 1979). Fatty acid synthesis in isolated spinach chloroplasts and in maize leaves is completely dependent on the presence of light, while in spinach leaf disks, the rate of fatty acid synthesis in the dark was reduced to 12–20% of the light rate (Browse et al, 1981). Expressing fatty acid composition in mole percentage of total fatty acyl chains, Browse et al (1981) found that there was a diurnal fluctuation of fatty acid composition in spinach leaves, with oleate (18:1) increasing in the light and linolenate (18:3). Like the previous workers, separated Arabidopsis leaf lipids into head group classes and analyzed the fatty acyl composition of each class, determining that PC, phosphatidylethanolamine (PE), and phosphatidylglycerol (PG) exhibited diurnal compositional variation, with 18:1 level highest in the www.frontiersin.org
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