Reducing nitrogen rate and increasing plant density benefit processing quality by modifying the spatial distribution of protein bodies and gluten proteins in endosperm of a soft wheat cultivar

To explore the potential ways for promoting biscuit-making quality of soft wheat, a field experiment was conducted to investigate the spatial distribution of protein bodies (PBs), gluten protein and processing quality in response to reducing nitrogen (N) rate and increasing plant density. A two-way factorial trial with three N rates (180, 120 and 0 kg ha(-1)) and three plant densities (180 x 10(4), 240 x 10(4) and 300 x 10(4) plants ha(-1)) was applied. The mature grains were milled into seven pearling fractions from the outermost to the innermost caryopses, denoted by Pl-P7. An inward decreasing trend was found in Zeleny sedimentation volume (ZSV) of fractions from the outer (P3) to inner endosperm layer (P7). Reducing N rate and increasing plant density both improved the processing quality of all pearling fractions. Moreover, reducing N rate showed a more remarkable effect on protein quality traits than increasing plant density, and their interaction effect was significant. The decrement in ZSV was most likely ascribed to the spatial variations in gluten proteins and glutenin macropolymers (GMPs). The accumulation and aggregation of PBs in caryopses were significantly declined by reducing N rate and increasing plant density. In addition, the protein quality traits in outer endosperm showed the largest variation, followed by that in middle and inner endosperm under various N rate and plant density. Thus, the combination of reducing N rate and increasing plant density might be a practical management approach for promoting biscuit-making quality in soft wheat.