Abstract
Gradients exist in the distribution of storage proteins in the wheat (Triticum aestivum) endosperm and determine the milling properties and protein recovery rate of the grain. A novel image analysis technique was developed to quantify both the gradients in protein concentration, and the size distribution of protein bodies within the endosperm of wheat plants grown under two different (20 or 28 °C) post-anthesis temperatures, and supplied with a nutrient solution with either high or low nitrogen content. Under all treatment combinations, protein concentration was greater in the endosperm cells closest to the aleurone layer and decreased towards the centre of the two lobes of the grain, i.e. a negative gradient. This was accompanied by a decrease in size of protein bodies from the outer to the inner endosperm layers in all but one of the treatments. Elevated post-anthesis temperature had the effect of increasing the magnitude of the negative gradients in both protein concentration and protein body size, whilst limiting nitrogen supply decreased the gradients.
Highlights
The starchy endosperm is the central storage tissue of the wheat grain and is the material from which white flour is produced
Grain yield was reduced by both increased post-anthesis temperature and reduced nitrogen supply, with a significant interaction between these two factors (P=0.008, F-test): reducing the nitrogen application rate had a greater effect on yield in plants grown under 20 /15 °C post-anthesis temperature conditions than in plants grown under 28 /15 °C post-anthesis temperature (Fig. 2A)
Nitrogen concentration at maturity was higher in grain grown under elevated post-anthesis temperature, and in grain grown under higher levels of applied nitrogen, with a significant interaction between these two factors (P=0.032, F-test): increasing nitrogen application rate increased grain nitrogen concentration to a greater extent in plants grown under high post-anthesis temperature than in plants grown under control conditions (Fig. 2B)
Summary
The starchy endosperm is the central storage tissue of the wheat grain and is the material from which white flour is produced. The milling of wheat grain is achieved through a sequence of milling and sieving stages, which results in the production of numerous mills streams. These individual mill streams are enriched with different parts of the wheat grain, and so gradients in endosperm protein concentration and composition will result in the production of mill streams with specific protein content, composition, and baking characteristics (Yahata et al, 2006; Wang et al, 2007; Wan et al, 2014; Zhou et al, 2018). Any increase in the gradient of protein concentration may result in an even greater amount of protein being lost during milling
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