Spatial distribution of functional components in the starchy endosperm of wheat grains

Peter R Shewry,Yongfang Wan,Malcolm J Hawkesford,Paola Tosi

doi:10.1016/j.jcs.2019.102869

Peter R Shewry, Yongfang Wan + Show 2 more

Open Access

https://doi.org/10.1016/j.jcs.2019.102869

Copy DOI

Abstract

The starchy endosperm of the mature wheat grain comprises three major cell types, namely sub-aleurone cells, prismatic cells and central cells, which differ in their contents of functional components: gluten proteins, starch, cell wall polysaccharides (dietary fibre) and lipids. Gradients are established during grain development but may be modified during grain maturation and are affected by plant nutrition, particularly nitrogen application, and environmental factors. Although the molecular controls of their formation are unknown, the high content of protein and low content of starch of sub-aleurone cells, compared to the other starchy endosperm cells types, may result from differences in developmental programming related to the cells having a separate origin (from anticlinal division of the aleurone cells). The gradients within the grain may be reflected in differences in the compositions of mill streams, particularly those streams enriched in the central and outer cells of the starchy endosperm, respectively, allowing the production of specialist flours for specific end uses.

Highlights

Wheat is used for a wide range of foods, from globally consumed forms such as bread, cakes, biscuits, pasta and noodles to regional and traditional foods such as couscous and bulgar
Sections of grain tissue can be analysed by various imaging approaches, ranging from simple light microscopy of stained and fixed tissues with components visualised by staining or immunochemistry, to sophisticated chemical imaging such as Fourier Transform Infrared (FT-IR) microspectroscopy (Barron et al, 2005; Toole et al, 2009, 2010, 2011), Raman microspectroscopy (Philippe et al, 2006; Toole et al, 2009), MALDI mass spectroscopy imaging (MSI) (Fanuel et al, 2018), and Secondary Ion Mass Spectrometry (NanoSIMS) (Moore et al, 2016)
Differences in protein content and composition have been known for many years, with the sub-aleurone cells being richer in protein and having fewer and less regular in shape starch granules, compared with other starchy endosperm cells (Bradbury et al, 1956; Kent, 1966; Kent and Evers, 1969)

Summary

Introduction

Wheat is used for a wide range of foods, from globally consumed forms such as bread, cakes, biscuits, pasta and noodles to regional and traditional foods such as couscous and bulgar. Sections of grain tissue can be analysed by various imaging approaches, ranging from simple light microscopy of stained and fixed tissues with components visualised by staining or immunochemistry, to sophisticated chemical imaging such as Fourier Transform Infrared (FT-IR) microspectroscopy (Barron et al, 2005; Toole et al, 2009, 2010, 2011), Raman microspectroscopy (Philippe et al, 2006; Toole et al, 2009), MALDI MSI (Fanuel et al., 2018), and Secondary Ion Mass Spectrometry (NanoSIMS) (Moore et al, 2016) These approaches are more readily applied to developing tissues than to mature grain, due to the ease of sectioning and the lower content of starch. The fractions still provide a broad view of the distribution of components within the whole grain

Protein

Linear gradients in the starchy endosperm

Modulation of gradients by nutrition and environment

Findings

Is it possible to exploit spatial gradients in grain utilisation?