Abstract
Leaf senescence is a developmental process critical for plant fitness, which involves genetically controlled cell death and ordered disassembly of macromolecules for reallocating nutrients to juvenile and reproductive organs. While natural leaf senescence is primarily associated with aging, it can also be induced by environmental and nutritional inputs including biotic and abiotic stresses, darkness, phytohormones and oxidants. Reactive oxygen species (ROS) are a common thread in stress-dependent cell death and also increase during leaf senescence. Involvement of chloroplast redox chemistry (including ROS propagation) in modulating cell death is well supported, with photosynthesis playing a crucial role in providing redox-based signals to this process. While chloroplast contribution to senescence received less attention, recent findings indicate that changes in the redox poise of these organelles strongly affect senescence timing and progress. In this review, the involvement of chloroplasts in leaf senescence execution is critically assessed in relation to available evidence and the role played by environmental and developmental cues such as stress and phytohormones. The collected results indicate that chloroplasts could cooperate with other redox sources (e.g., mitochondria) and signaling molecules to initiate the committed steps of leaf senescence for a best use of the recycled nutrients in plant reproduction.
Highlights
Leaf senescence is an ordered physiological process in which cellular structures and biomolecules are progressively broken down and the resulting products mobilized to other plant organs such as fruits, seeds, tubers and/or more apical leaves [1,2,3]
Chloroplasts are main targets for degradation during leaf senescence and provide the bulk of recycled nutrients for the development of reproductive organs, especially nitrogen compounds resulting from protein and Chl breakdown
Results obtained in the last few years, indicate that chloroplasts contribute signals that affect leaf senescence at an early stage and at a hierarchically high level of developmental decisions [32,86,87,88,89,97]
Summary
Leaf senescence is an ordered physiological process in which cellular structures and biomolecules are progressively broken down and the resulting products mobilized to other plant organs such as fruits, seeds, tubers and/or more apical leaves [1,2,3]. Mutants exhibiting delayed leaf senescence have been described in many species and are extremely useful to identify gene products involved in cell aging, cell death and nutrient. Mutants exhibiting delayed leaf senescence have 2been described in many species and are extremely useful to identify gene products involved in cell aging, cell death and nutrient salvage [1,11,12,13,14]. Our knowledge on the participation of chloroplast redox chemistry in plant and programmed cell death lags behind that of animal mitochondria, an increasing number of studies senescence and programmed cell death lags behind that of animal mitochondria, an increasing indicate that plastids might be playing a more important role than thought before during leaf senescence.
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