Sugar Partitioning and Source‐Sink Interaction are Key Determinants of Leaf Senescence in Maize

Source–sink communication is one of the key regulators of senescence; however, the mechanisms underlying such regulation are largely unknown. We analysed senescence induced by the lack of grain sink in maize, termed source–sink regulated senescence (SSRS), and compared the associated physiological and metabolic changes with those accompanying natural senescence. Phenotypic characterization of 31 diverse field‐grown inbreds revealed substantial variation for both SSRS and natural senescence. Partitioning of excess carbohydrates to alternative sinks, mainly internodes and husks, emerged as a critical mechanism underlying both SSRS and stay‐green. Time‐course analyses of SSRS sensitive (B73) and resistant (PHG35) inbreds confirmed the role of sugar partitioning in SSRS and stay‐green. Elevated hemicellulose content in PHG35 internodes highlighted the role of the cell wall as a significant alternative sink. Sugar signalling emerged as an important regulator of SSRS as evident from an increased accumulation of trehalose‐6‐phosphate and decreased transcript levels of snf1‐related protein kinase1, two signalling components associated with senescence, in B73. These findings demonstrate a crucial role of sugar partitioning, signalling, and utilization in SSRS. Available genetic variation for SSRS and a better understanding of the underlying mechanisms would help modify sugar partitioning and senescence to enhance the productivity of maize and related grasses.