Lipid Partitioning in Maize (Zea mays L.) Endosperm Highlights Relationships among Starch Lipids, Amylose, and Vitreousness

Abstract

Content and composition of maize endosperm lipids and their partition in the floury and vitreous regions were determined for a set of inbred lines. Neutral lipids, i.e., triglycerides and free fatty acids, accounted for more than 80% of endosperm lipids and are almost 2 times higher in the floury than in the vitreous regions. The composition of endosperm lipids, including their fatty acid unsaturation levels, as well as their distribution may be related to metabolic specificities of the floury and vitreous regions in carbon and nitrogen storage and to the management of stress responses during endosperm cell development. Remarkably, the highest contents of starch lipids were observed systematically within the vitreous endosperm. These high amounts of starch lipids were mainly due to lysophosphatidylcholine and were tightly linked to the highest amylose content. Consequently, the formation of amylose-lysophosphatidylcholine complexes has to be considered as an outstanding mechanism affecting endosperm vitreousness.

Responses to Hypoxia and Endoplasmic Reticulum Stress Discriminate the Development of Vitreous and Floury Endosperms of Conventional Maize (Zea mays) Inbred Lines

“…This difference was found to be more acute at 20 DAP. It is interesting to note that ER stress was previously associated with higher content of triacylglycerols (TAG) in maize endosperm of the floury2 mutant (Shank et al, 2001), in accordance with higher amounts of these storage lipids in the floury regions of conventional maize (Gayral et al, 2015). The higher TAG deposition in MEC relative to that in MEP is also related to major changes in the proteins that cover and stabilize oil droplets.…”

“…In fact, these sucrose levels decrease from the basal to the upper endosperm (Doehlert and Kuo, 1990), following exactly the opposite gradient observed for starch accumulation (Dochlert, 1990). Therefore, the higher amount of soluble sugars in MEC is obviously in total discordance with the higher amounts of starch observed in the floury endosperm (Gayral et al, 2015). Conversely, the lower amounts of almost all free amino acids found in MEP, when compared with those in MEC (Figure 4B), are quite consistent with the significant level of protein synthesis in MEP, leading to a higher protein accumulation in the vitreous region of mature endosperm (Gayral et al, 2016).…”

“…Any differential expression is observed for sus-sh1 (GRMZM2G089713) that encodes SUS-SH1 (Figure S2) in agreement with the fact that the expression of this gene is not up-regulated by hypoxia but by anoxia, a huge depletion of oxygen (Zeng et al, 1998). However, up-regulation of sus1 and sus2 in MEP is contradictory to (i) slightly lower starch contents in the vitreous than in the floury endosperm (Gayral et al, 2015) and (ii), as shown below, to up-regulation of genes markers of hypoxia in MEC. Altogether these results suggest that the management of hypoxia differs between MEP and MEC.…”

“…The inbred lines L3 (flint) and L5 (dent) were chosen from a previous study where 13 flint and dent inbred lines were analyzed for their protein, starch, and lipid contents in relation to endosperm vitreousness (Gayral et al, 2015, 2016). Two biological repetitions were carried out with grains from different ears.…”

“…Amylose content follows the same distribution, leading to a starch crystallinity gradient. This starch crystallinity is also affected by higher amounts of starch-bound lipids in the vitreous area (Gayral et al, 2015). These gradients are in agreement with the centrifugal development of endosperm from mitotic cell division to programmed cell death (PCD).…”