Foliar ¹⁵N-urea absorption and translocation in wheat with contrasting senescence patterns at late growth stage

Nitrogen (N) is essential for preserving green leaf area in wheat during the late growth phases and for postponing senescence. This research examined foliar N uptake, translocation, and redistribution in stay-green (YM66) and early-senescent (WM6) wheat plants treated with ¹⁵N-labeled urea applied to flag leaves before and after anthesis. The redistribution of absorbed ¹⁵N was observed during the grain-filling phase. Post-anthesis, YM66 exhibited a larger green leaf area and higher chlorophyll content compared to WM6 and demonstrated superior foliar ¹⁵N uptake at both administration periods. At maturity, 51-56% of the absorbed ¹⁵N before anthesis was detected in the grain, but 19-30% and 18-25% were retained in the leaves and stems, respectively. After post-anthesis treatment, 40-48.7% of absorbed ¹⁵N was remobilized to the grain, whereas the majority remained in vegetative tissues. The data indicate that grain N in both genotypes primarily originates from N assimilated before anthesis, and that the stay-green genotype shows improved foliar N uptake and redistribution during grain filling. The results offer a physiological insight into N dynamics linked to differing senescence behaviors in wheat.