The Role of Oxidative Metabolism in the Regulation of Leaf Senescence by the Light Environment

Senescence is a genetically controlled process whose regulation depends on many factors. Leaf senescence begins with the catabolism of chlorophyll and macromolecules such as proteins and membrane lipids, a process that is accompanied by the alteration of organelles and, ultimately, the breakdown of nuclear components. In annual plants, reproduction is the main event that triggers leaf senescence. However, several environmental factors may initiate and/or modulate it both in the vegetative as well as the reproductive stages. An important exogenous factor is light, and both its senescence-inhibiting or -promoting qualities are described. Both the darkening of individual leaves as well as exposure to high light intensities can induce senescence, and it has been proposed that changes in the redox status of cells associated with the overproduction of reactive oxygen species (ROS) might be the basis of the senescence symptoms. In dense stands, basal leaves frequently senesce before anthesis, and there is evidence that this phenomenon is regulated by changes in light quantity and quality. While models about putative signalling pathways leading to either acclimation or to cell death involving the accumulation of ROS in response to excess light have been recently developed, less information is available with regards to the biochemistry of leaf senescence induced by changes in light spectral quality. In the present review we summarize a series of studies that have contributed to the view that changes in either light quantity or quality may modulate leaf senescence through signals derived from oxidative metabolism. _____________________________________________________________________________________________________________