Leaf senescence, a type of programmed cell death, is a complex and highly regulated process that involves the degradation of macromolecules, including proteins, nucleic adds, and lipids. Nutrients, especially nitrogen, are re-mobilized from senescing leaves to newly developing tissues or reserve organs. Our review focuses on three pathways for protein breakdown and the resorption of N during this process: the ubiquitin/proteosome system, the chloroplast degradation pathway, and the vacuolar and autophagic pathway. We propose that two relative biochemical cycles exist for amino add recycling and N-export -- the GS/GOGAT cycle and the PPDK-GS/GOGAT cycle.