Yang Weili, Pollard Mike, Li-Beisson Yonghua, Ohlrogge John
Department of Plant Biology, Michigan State University, 48824-1312, USA.
Department of Plant Biology, Michigan State University, 48824-1312, USA.
Phytochemistry. 2016 Oct;130:159-69. doi: 10.1016/j.phytochem.2016.03.017. Epub 2016 May 19.
Cutin is an extracellular lipid polymer that contributes to protective cuticle barrier functions against biotic and abiotic stresses in land plants. Glycerol has been reported as a component of cutin, contributing up to 14% by weight of total released monomers. Previous studies using partial hydrolysis of cuticle-enriched preparations established the presence of oligomers with glycerol-aliphatic ester links. Furthermore, glycerol-3-phosphate 2-O-acyltransferases (sn-2-GPATs) are essential for cutin biosynthesis. However, precise roles of glycerol in cutin assembly and structure remain uncertain. Here, a stable isotope-dilution assay was developed for the quantitative analysis of glycerol by GC/MS of triacetin with simultaneous determination of aliphatic monomers. To provide clues about the role of glycerol in dicarboxylic acid (DCA)-rich cutins, this methodology was applied to compare wild-type (WT) Arabidopsis cutin with a series of mutants that are defective in cutin synthesis. The molar ratio of glycerol to total DCAs in WT cutins was 2:1. Even when allowing for a small additional contribution from hydroxy fatty acids, this is a substantially higher glycerol to aliphatic monomer ratio than previously reported for any cutin. Glycerol content was strongly reduced in both stem and leaf cutin from all Arabidopsis mutants analyzed (gpat4/gpat8, att1-2 and lacs2-3). In addition, the molar reduction of glycerol was proportional to the molar reduction of total DCAs. These results suggest "glycerol-DCA-glycerol" may be the dominant motif in DCA-rich cutins. The ramifications and caveats for this hypothesis are presented.
角质是一种细胞外脂质聚合物，有助于陆地植物形成抵御生物和非生物胁迫的保护性角质层屏障功能。甘油已被报道为角质的一种成分，其重量占总释放单体的14%。先前使用富含角质层的制剂进行部分水解的研究证实了存在具有甘油 - 脂肪族酯键的寡聚物。此外，甘油 - 3 - 磷酸2 - O - 酰基转移酶（sn - 2 - GPATs）对于角质生物合成至关重要。然而，甘油在角质组装和结构中的精确作用仍不确定。在此，开发了一种稳定同位素稀释法，通过气相色谱/质谱联用仪对三乙酸甘油酯中的甘油进行定量分析，同时测定脂肪族单体。为了提供关于甘油在富含二羧酸（DCA）的角质中的作用线索，该方法被应用于比较野生型（WT）拟南芥角质与一系列角质合成有缺陷的突变体。WT角质中甘油与总DCA的摩尔比为2:1。即使考虑到羟基脂肪酸的少量额外贡献，这一甘油与脂肪族单体的比例也远高于此前报道的任何角质。在所分析的所有拟南芥突变体（gpat4/gpat8、att1 - 2和lacs2 - 3）的茎和叶角质中，甘油含量均大幅降低。此外，甘油的摩尔减少量与总DCA的摩尔减少量成正比。这些结果表明“甘油 - DCA - 甘油”可能是富含DCA的角质中的主要基序。本文还介绍了这一假设的影响和注意事项。
