Characterization of Markers to Determine the Extent and Variability of Leaf Senescence in Arabidopsis. A Metabolic Profiling Approach

Abstract

Comparison of the extent of leaf senescence depending on the genetic background of different recombinant inbred lines (RILs) of Arabidopsis (Arabidopsis thaliana) is described. Five RILs of the Bay-0 3 Shahdara population showing differential leaf senescence phenotypes (from early senescing to late senescing) were selected to determine metabolic markers to discriminate Arabidopsis lines on the basis of senescence-dependent changes in metabolism. The proportion of g-aminobutyric acid, leucine, isoleucine, aspartate, and glutamate correlated with (1) the age and (2) the senescence phenotype of the RILs. Differences were observed in the glycine/serine ratio even before any senescence symptoms could be detected in the rosettes. This could be used as predictive indicator for plant senescence behavior. Surprisingly, late-senescing lines appeared to mobilize glutamine, asparagine, and sulfate more efficiently than early-senescing lines. The physiological basis of the relationship between leaf senescence and flowering time was analyzed.Leaf senescence is a key developmental step in the life of annual plants. During growth, green leaves accumulate nutrients. The main purpose of senescence is the mobilization and recycling of these nutrients to the developing seeds to prepare the next generation. Developmental signals, aging, or stress can induce leaf senescence. The final stage of this process is death, but cell death is actively delayed until nutrients have been removed (Buchanan-Wollaston et al., 2003).During senescence, cell constituents are dismantled in an ordered progression. Chlorophyll degradation is the first visible symptom of senescence, but by the time yellowing can be seen, some senescence has already occurred. Chlorophyll, protein, and lipid degradation processes have been largely investigated (Hö rtensteiner and Feller, 2002). Protein and mRNA degradation parallels the loss in photosynthetic activity and participates in nutrient mobilization. Nucleic acids, especially RNA, form a valuable source of phosphorus in mature leaves. Total RNA levels fall rapidly during senescence, whereas nuclear DNA is maintained to allow gene expression to continue, until late in the process. Nutrients such as sulfur, phosphorus, metal ions, and minerals are also transferred out of the leaves (Himelblau and Amasino, 2001). Accelerated metabolism of membrane lipids results in a decline in the structural and functional integrity of cellular membranes. Thylakoid membranes provide an abundant source of carbon that can be mobilized for use as an energy source during senescence. Rubisco is one of the major sources of nitrogen for mobilization. A major question in leaf senescence is how leaf proteins, up to 75% of which are located within the chloroplast, are degraded and mobilized (Mae, 2004).The molecular events that induce and contribute to the senescence process have recently been extensively investigated. The genomic resources that are now available for Arabidopsis (Arabidopsis thaliana) have allowed the rapid identification of ...

The Response of Diatom Central Carbon Metabolism to Nitrogen Starvation Is Different from That of Green Algae and Higher Plants

“…In higher plants and green algae, photosynthetic carbon fixation is also reduced in response to nitrogen deprivation, and excess carbon is generally stored in molecular pools that contain little or no nitrogen. In higher plants, this is usually in the form of starch (Diaz et al, 2005;Wingler et al, 2006), and Peng et al (2007) described increased transcript levels of two genes involved in starch biosynthesis in Arabidopsis (Arabidopsis thaliana) under nitrogen starvation. In the fresh water green alga Chlamydomonas reinhardtii, on the other hand, excess carbon is reportedly directed to fatty acid biosynthesis (Wang et al, 2009;Moellering and Benning, 2010), and Miller et al (2010) found increased expression of genes involved in lipid biosynthesis in C. reinhardtii when nitrogen was not available.…”

Comprehensive Dissection of Spatiotemporal Metabolic Shifts in Primary, Secondary, and Lipid Metabolism during Developmental Senescence in Arabidopsis

“…Therefore, in order to consider the evidence of specific roles for metabolites in senescence, a more precise analysis of metabolite levels in different tissues and cell types during the process of senescence is required. Although, to date, a number of targeted metabolite profiles, particularly those focused on lipids as seed storage compounds (Yang and Ohlrogge, 2009;Seltmann et al, 2010) and sugars, amino acids, and nutrient ions (Masclaux et al, 2000;Quirino et al, 2001;Stessman et al, 2002;Diaz et al, 2005;Masclaux-Daubresse et al, 2005, 2007Pourtau et al, 2006;Wingler et al, 2006Wingler et al, , 2012, have been generated from maturing and senescing tissues, a broad overview of metabolic changes during senescence, including the interactions between various metabolic pathways, is still lacking. Therefore, we performed a metabolomics study to obtain comprehensive metabolite profiles, including primary and secondary metabolites and lipids, over the course of developmental senescence in rosette leaves before and after bolting and siliques of Arabidopsis in order to investigate the metabolic response and spatiotemporal distribution of metabolites during senescence at the whole-plant level and within single leaves.…”

“…This allowed us to capture metabolite changes during the sink-source transition within a single leaf and to identify differences in metabolic patterns between presenescent and senescent tissues. This provides a spatiotemporal standard catalog of metabolites with which experiments affecting developmental processes, such as nutrient deficiency-induced senescence (Diaz et al, 2005;Watanabe et al, 2010;Obata and Fernie, 2012) or others, can be compared as well as marker metabolites for distinct senescence stages. The results are discussed in the context of current models of the metabolic shifts underlying developmental senescence.…”

Cold tolerance in cypress (Cupressus sempervirens L.): a physiological and molecular study

“…Another trait which has been found to interact with cold acclimation is leaf senescence (Masclaux-Daubresse et al 2007). During low-temperature exposure plants accumulate sugars (Cook et al 2004), an event that has been found to coincide with the onset of senescence in Arabidopsis and tobacco (Masclaux et al 2000;Diaz et al 2005). Cold acclimation in many woody plants is initially induced by short photoperiod and low, non-freezing temperatures.…”