Analysis of the protein distribution within the wheat endosperm

Starchy endosperm proteins determine wheat quality and exhibit, besides a quantitative protein gradient, a qualitative protein gradient from the outer to inner starchy endosperm. The goal was to investigate the relative differences in protein composition between the aleurone, sub-aleurone and inner endosperm. Using laser microdissection followed by nanoLC-MS/MS, an innovative method combining a high spatial specificity and analytical selectivity in sample-limited situations, 780 proteins were detected and classified by function. Relatively more gluten proteins were detected in the sub-aleurone compared to inner endosperm. Gluten composition-wise, the sub-aleurone is relatively more enriched in ω-gliadins, but impoverished in LMW-GS and γ-gliadins. While a basic set of albumins and globulins is detected across the entire endosperm, some proteins, like puroindoline-B, display an increasing (or decreasing) gradient. Histological origin and relative positioning of the endosperm cells are hypothesized to drive the protein gradient. Knowledge on this gradient provides major opportunities for the wheat manufacturing industry.