Abstract
Leaf senescence in plants is a coordinated process that involves remobilization of nutrients from senescing leaves to sink tissues. The molecular events associated with nutrient remobilization are however not well understood. In this study the tobacco system with a source-sink relationship between different leaf positions was used in analyzing the spatiotemporal changes of 76 metabolites from leaves at 3 different stalk positions and 8 developmental stages. The metabolomic data was then compared with RNA-seq data from the same samples to analyze the activities of the metabolic pathways that are important for nutrient remobilization. Integrative analyses on metabolites accumulation and expression changes of enzyme-encoding genes in corresponding metabolic pathways indicated a significant up-regulation of the tricarboxylic acid cycle and related metabolism of sugars, amino acids and fatty acids, suggesting the importance of energy metabolism during leaf senescence. Other changes of the metabolism during tobacco leaf senescence include increased activities of the GS/GOGAT cycle which is responsible for nitrogen recycling, and increased accumulation of nicotine. The results also suggested that a number of compounds seemed to be transported from senescing leaves at lower positions to sink leaves at upper positions. Some of these metabolites could play a role in nutrient remobilization.
Highlights
Leaf senescence in plants is a coordinated process that involves remobilization of nutrients from senescing leaves to sink tissues
Metabolic pathways were analyzed via combining changes of related metabolites with the expression profiling of genes encoding for biosynthetic enzymes/transporters
We have identified a number of metabolic processes that showed changes in activities during leaf senescence
Summary
Leaf senescence in plants is a coordinated process that involves remobilization of nutrients from senescing leaves to sink tissues. Integrative analyses on metabolites accumulation and expression changes of enzyme-encoding genes in corresponding metabolic pathways indicated a significant up-regulation of the tricarboxylic acid cycle and related metabolism of sugars, amino acids and fatty acids, suggesting the importance of energy metabolism during leaf senescence. The results suggested that a number of compounds seemed to be transported from senescing leaves at lower positions to sink leaves at upper positions Some of these metabolites could play a role in nutrient remobilization. Leaf senescence in crop plants influences agricultural yield through two different processes: photosynthesis and nutrient remobilization. The execution processes of leaf senescence, including the degradation of macromolecules and remobilization of nutrients, are controlled by differential gene expression. Knockout of cytosolic GS genes reduced N remobilization as well as seed yield in Arabidopsis[19]
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