Distinct gradients exist in the distribution of protein within the wheat endosperm (Cobb 1905; Kent 1966; Tosi et al. 2011), with protein accumulation concentrated towards the
outer endosperm. Due to these gradients, during milling mill streams of differing protein content and bread-making quality are produced (Wang et al. 2007). Furthermore, during
milling for white flour a portion of the outer endosperm remains adhered to the removed aleurone layer, resulting in a disproportionate loss of protein.
By 2080, average summer temperatures in the UK are predicted to rise by up to 4.2°C, and heatwaves will become increasingly common (Jenkins et al. 2009). The effect that
these changes will have on the distribution of protein within the wheat grain is yet to be discovered.
Controlled-environment and field trial experiments were used to investigate the effects of nitrogen input, temperature during grain-filling, and genotype on wheat grain protein distribution, protein quality and related gene expression, grain yield, and yield components. In addition to established techniques, a novel image analysis method was
developed to quantify the protein distribution gradients in light-microscopy images of wheat grain.
Across both field and controlled-environment experiments, increasing nitrogen supply during vegetative development resulted in an increase in the protein distribution gradient in the wheat endosperm, with a greater proportion of protein accumulated towards the aleurone layer. Furthermore, elevated temperature during grain-filling was found
to interact with nitrogen input, increasing the gradient in protein accumulation to a greater degree under high-nitrogen input conditions. In the field, the response to nitrogen varied between genotypes, with the high-protein bread-making varieties showing the greatest response. These grain protein distribution gradient results are supplemented by analyses of the size-distribution of protein bodies in the wheat endosperm, grain protein composition with regards to bread-making quality, gluten protein synthesis gene expression, and grain yield and yield components.