Foliar applications of various nitrogen (N) forms to winter wheat affect grain protein accumulation and quality via N metabolism and remobilization

Foliar nitrogen (N) application is an effective strategy to improve protein content and quality in wheat kernels, but the specific effects of N forms remain unclear. In a two-year field study, foliar application of various N forms (NO3 , urea, NH thorn 4) at anthesis was performed to measure their effects on wheat grain protein accumulation, quality formation, and the underlying mechanisms. Foliar application of three N forms showed varying effects in improving grain gluten proteins and quality traits. Under NH thorn 4 applica-tion, there was more post-anthesis N uptake for grain filling, with relatively strong increase in enzyme activities and gene expression associated with N metabolism in flag leaves at 8-20 days after anthesis (DAA), whereas its promotion of grain N metabolism became weaker after 20 DAA than those under NOi and urea treatments. More N was remobilized from source organs to grain under treatment with foliar NOi and urea. Genes controlling the synthesis of gluten protein and disulfide bonds were upregu-lated by NO3-and urea at 20-28 DAA, contributing to increased grain protein content and quality. Overall, foliar applications of NOi and urea were more effective than those of NH thorn 4 in increasing grain N filling. These findings show that manipulating the source-sink relationship by reinforcing grain N metabolism and N remobilization is critical for optimizing grain protein accumulation and quality formation.(c) 2021 Crop Science Society of China and Institute of Crop Science, CAAS. Production and hosting by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY-NC -ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).