Nitrogen redistribution during the grain-filling stage and its correlation with senescence and TaATG8 expression in leaves of winter wheat

1. The rate of nitrogen redistribution serves as a measure of nitrogen transport capacity. 2. Nitrogen application hinders nitrogen transport during the initial phase of grouting, but enhances it in the intermediate and later stages. 3. Concurrent with the peak expression of autophagy genes, the transportation of potential amino acids is likewise heightened. Nitrogen is a key nutrient for wheat ( Triticum aestivum L.) growth and yield, particularly during the grain-filling stage, where most nitrogen is redistributed from vegetative organs to the grain, significantly influencing yield. However, the period in which nitrogen translocation from the vegetative phase to grain maturation occurs and its correlation with flag leaf senescence remains unclear. In this study, a field experiment was conducted using the winter wheat cultivar ‘Xinong 511’ under two nitrogen fertilizer treatments: regular nitrogen supply (240 kg ha -1 [N 240 ]) and no nitrogen supply (0 kg ha -1 [N 0 ]). The results revealed that nitrogen accumulation in wheat flag leaves peaked at 7-14 days, with 4.55% nitrogen content, after which nitrogen was redistributed to the grains. Nitrogen content in flag leaves decreased by 56% during 21-35 days, while that in the grains increased by 51%. The Plant Analysis Development value (relative chlorophyll content), photosynthetic rate, free amino acid concentration, and soluble protein content in flag leaves peaked at 7-14 days, indicating nitrogen transportation from the flag leaves to the grains. Nitrogen application significantly increased the nitrogen remobilization rate in flag leaves by 20% compared with that of N 0 , reduced reactive oxygen species accumulation by 21%, and delayed flag leaf senescence. Under nitrogen deficiency, autophagy was induced earlier, with a 5–7-fold increase in the expression of autophagy-related genes ( TaATG8 ), suggesting that regulating the autophagy pathway and enhancing autophagy activity optimizes nitrogen fertilization. Our study demonstrates that the remobilization of nitrogen from vegetative parts to grains initiates leaf senescence and is closely correlated with the expression of autophagy-related genes.