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

Abstract

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.