The progression of leaf senescence is gated by the cytosolic arginine pool

Leaf senescence aims to degrade cellular components to recover valuable nutrients and reallocate them to other organs¹. Once this remobilization is complete, cells undergo a vacuolar-type of programmed cell death², ultimately leading to the death of the entire organ. But how do cells from a senescing leaf 'know' when to die? If the cell death process per se is initiated too early, remobilization may not be completed, rendering it futile. This suggests the presence of a 'sensing' mechanism that coordinates the remobilization phase with the onset of cell death during leaf senescence. Here, using Arabidopsis thaliana functional stay-green mutants, we show that senescing cells are wired to metabolically dissipate the cytosolic arginine pool, which otherwise represses the progression of leaf senescence. We propose a model in which a senescing cell uses this pool as a proxy for the completion of nitrogen remobilization and to accurately time the subsequent induction of cell death.