Putrescine catabolism integrates nitrogen remobilization, redox homeostasis, and senescence signaling in barley leaf

Efficient nitrogen use is a critical factor for sustainable crop production and environmental stewardship, yet the molecular mechanisms underlying nitrogen remobilization during leaf senescence remain incompletely understood. We hypothesize that polyamine catabolism particularly that of putrescine (Put) via copper-containing amine oxidase (CuAO) - is a regulatory node integrating nitrogen remobilization and senescence signaling in barley leaves. Using a transcriptomic approach, we compared the expression of nitrogen metabolism-related genes (NMGs) during dark-induced leaf senescence (DILS) and developmental leaf senescence (DLS) in barley (Hordeum vulgare, Hv). Our findings reveal distinct expression patterns of HvNMGs between DILS and DLS, suggesting the involvement of different regulatory mechanisms. Notably, genes associated with polyamine biosynthesis and catabolism were upregulated during DILS, indicating their role in nitrogen recycling. To further investigate the role of Put catabolism, we analyzed the metabolite profiles of dark-incubated leaves and leaves treated with both darkness and aminoguanidine - a potent inhibitor of Put catabolism. Inhibition of Put catabolism accelerated senescence resulting in a statistically significant reduction of Fv/Fm, compared to DILS alone, disrupted metabolic homeostasis, and altered redox signaling, likely through the dysregulation of nitric oxide and nitroxyl levels. Furthermore, impaired Put catabolism led to excessive urea accumulation from 2,55-fold to 11-fold on following days of senescence and disrupted nitrogen homeostasis. These results demonstrate that Put catabolism plays a regulatory role in coordinating nitrogen remobilization, redox balance, and stress signaling during leaf senescence in barley. This pathway appears essential for maintaining the balance between nitrogen recycling and the progression of senescence. Our findings provide new insights into the metabolic reprogramming during leaf senescence and highlight potential targets for improving nitrogen use efficiency in cereal crops.