Distribution of cell wall hemicelluloses in the wheat grain endosperm: a 3D perspective
Uneven distribution of AX and BG in lateral and longitudinal dimensions of a wheat grain was observed by three-dimensional MS imaging, presumably related to specific physicochemical properties of cell walls.
Arabinoxylans (AX) and β-glucans (BG) are the main hemicelluloses that comprise the primary walls of starchy endosperm. These components are not evenly distributed in the endosperm, and the impact of their distribution on cell wall properties is not yet fully understood. Combined with on-tissue enzymatic degradation of the cell walls, mass spectrometry imaging (MSI) was used to monitor the molecular structure of AX and BG in thirty consecutive cross-sections of a mature wheat grain. A 3D image was built from the planar images, showing the distribution of these polymers at the full-grain level, both in lateral and longitudinal dimensions. BGs were more abundant at the vicinity of the germ and in the central cells of the endosperm, while AX, and especially highly substituted AX, were more abundant close to the brush and in the cells surrounding the crease (i.e., the transfer cells). Compared with the previously reported protocol, significant improvements were made in the tissue preparation to better preserve the shape of the fragile sections. This allowed to us achieve a good-quality 3D reconstruction from the consecutive 2D images. By providing a continuous view of the molecular distribution of the cell wall components across and along the grain, the three-dimensional images obtained by MSI may help understand the structure–function relationships of cell walls. The method should be readily extendable to other parietal polymers by selecting the appropriate enzymes.
Keywords3D-image Arabinoxylan Cell walls Endosperm β-Glucan Mass spectrometry imaging Wheat
Mass spectrometry imaging
The authors would like to thank Camille Alvarado (INRA UR1268 BIA, Nantes, France) for the acquisition of the fluorescence microscopy images proposed as Supporting information. The authors also thank Arndt Asperger and Sabine Jourdain from Bruker (Bremen, Germany) for their valued assistance regarding the use of the SCiLS Lab software.
Compliance with ethical standards
Conflict of interest
The authors certify that there are no conflict of interests with any financial organization regarding the material discussed in the manuscript.
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