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

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, it remains unclear during which period the nitrogen translocation from the vegetative phase to grain maturation occurs and how it correlates with flag leaf senescence. 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 (N₂₄₀)) and no nitrogen supply (0 kg ha^–1 (N₀)). The results revealed that nitrogen accumulation in wheat flag leaves peaked at 7–14 days, with a nitrogen content 4.55%, 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 N₀, 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 regulation of the autophagy pathway and enhancement of autophagy activity can optimize 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.