Monoacylglycerol (MAG) in Plants: Functional Diversity of
KeywordsNeutral Lipid Glycerol Backbone Ionization Tandem Mass Spectrometry Electrospray Ionization Tandem Mass Spectrometry Saturated Acyl
lipophilic polymer found in specialized cell to insulate cells or tissue from surrounding cells
Structure and Occurrence
The composition of MAG is quite diverse depending on their occurrence. Like other neutral lipids, MAG can be found in the seed oil, but only in minor amounts (Hirayama and Hujii 1965; Panekina et al. 1978). MAG is also detected in developing seeds. In maturing soybean seeds, MAG comprised the major neutral lipid 20 days after flowering although the amount decreased rapidly in further developmental stages (Hirayama and Hujii 1965). MAGs are also a substantial part of surface wax of leaves and fruits, and here preferentially an ω-hydroxy acid is esterified to the glycerol backbone (Graça et al. 2002; Simpson and Ohlrogge 2016). MAGs are also a part of suberin and were detected, for example, in suberin of cork, containing α,ω-dicarbolic acids (Graça and Santos 2006) as well as in suberin of root wax in Arabidopsis thaliana, where the esterified component was identified as saturated acyl chains of C22 – C30 (Li et al. 2007).
MAG functions predominantly as the precursor in the TAG biosynthesis via different pathways. It was shown that in developing peanut cotyledons (Tumaney et al. 2001, Parthibane et al. 2012), DAG is produced from MAG by acyl-CoA/monoacylglycerol acyltransferase (MGAT), similar to DAG synthesis in mammalians. MAG also takes part in transacylating reactions producing DAG or lysophosphatidylcholine in developing seeds (Stobart et al. 1997) or in surface wax of fruits (Simpson and Ohlrogge 2016). Besides the function in TAG biosynthesis, MAG also plays a role in cutin biosynthesis (Petit et al. 2016). It was suggested that sn2-MAG or β-MAG is acting as precursor in cutin and surface wax assembly, as it can be exported by epidermal cells (Yang et al. 2010; Simpson and Ohlrogge 2016).
Detection of MAG in Plant Lipid Extracts
MAGs may be analyzed in similar way to other neutral lipids via thin-layer chromatography (TLC), followed by gas chromatography (GC) to determine their fatty acid composition. Additionally MAG can be analyzed in lipidomic studies via electrospray ionization tandem mass spectrometry (ESI-MS).
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