Senescence in Plants

Abstract

Plant senescence is the final stage of development during which the plant recycles the valuable cellular building blocks that have been deposited in the leaves and other parts of the plant during growth. These reusable nutrients are then stored in the plant until they can be used in new growth or sent to the seed to provide a nutrient store for the next generation. Maintaining an efficient senescence process is therefore essential for the fitness of the plant or its seed. Senescence is a complex, highly regulated process that requires new gene expression and involves the interactions of many signalling pathways. In crops inappropriately timed senescence can reduce final crop yield, and in many vegetable crops significant postharvest loss is due to senescence. Unravelling the regulatory mechanisms that underlie senescence may have significant impact on increasing future food production.

Key Concepts

  • Plant senescence is a recycling process.
  • Senescence confers an adaptive advantage to a plant increasing its fitness or reproductive success.
  • Initiating senescence triggers a regulated series of events that dismantle, degrade and then mobilise valuable cellular processes.
  • The majority of a leaf protein and lipid component is in the chloroplast and it undergoes dramatic structural changes during senescence.
  • Chlorophyll needs to be rapidly degraded during senescence to ensure cells do not die due to phototoxicity.
  • Proteins degraded during senescence release valuable nitrogen and other minerals for mobilisation.
  • Thousands of genes are involved in the regulation of senescence.
  • Most of the major plant hormones have roles in the regulation of senescence.

Keywords: plant senescence; nitrogen; chloroplast; development; signalling pathways; stress responses; protein degradation

Figure 1. Illustrations of plant senescence: (a) Autumnal senescence in a beech wood, Derbyshire. (b) Total senescence in the entire wheat plant results in all mobilisable nutrients being stored in the grain. (c) Leaf senescence showing differential progression of senescence in the leaf. Areas close to the veins senesce last.
Figure 2. Changes in the leaf during development. (a) Change in chlorophyll levels as senescence progresses. (b) Change in visual appearance of leaf 7 harvested from Col0 plants at different time points during development. (c) Gene expression changes during leaf development. GeneSpring (Silicon Genetics) analysis shows two clusters of genes; each line shows the changes in expression of a single gene, those in red show increased expression during development while those in blue show a decrease. SAG12 is one of the genes in the red cluster; several chlorophyll binding proteins and other photosynthetic proteins are in the blue cluster.
Figure 3. Potential functions of genes up or downregulated during senescence. Gene ontology (GO) annotations were applied to the groups of genes that were either upregulated or downregulated during senescence. Senescence‐enhanced genes (sen) are in pale green, while genes downregulated in senescence (MG) are shown in dark green. Functional classifications are shown under each pair of cones and the numbers of genes in each group are shown in the table.
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Further Reading

Avila‐Ospina L, Moison M, Yoshimoto K and Masclaux‐Daubresse C (2014) Autophagy, plant senescence, and nutrient recycling. Journal of Experimental Botany 65: 3799–3811.

Breeze E, Harrison E, McHattie S, et al. (2011) High‐resolution temporal profiling of transcripts during Arabidopsis leaf senescence reveals a distinct chronology of processes and regulation. The Plant Cell 23: 873–894.

Buchanan‐Wollaston V, Page T, Harrison E, et al. (2005) Comparative transcriptome analysis reveals significant differences in gene expression and signalling pathways between developmental and dark/starvation induced senescence in Arabidopsis. Plant Journal 42: 567–585.

Gan S (2007) Senescence Processes in Plants. Annual Plant Reviews, vol. 26. Blackwell Publishing: Ames, IA.

Hörtensteiner S (2006) Chlorophyll degradation during senescence. Annual Review of Plant Biology 57: 55–77.

Hörtensteiner S and Kräutler B (2011) Chlorophyll breakdown in higher plants. Biochimica et Biophysica Acta 1807: 977–988.

Khan M, Rozhon W and Poppenberger B (2014) The role of hormones in the aging of plants – a mini‐review. Gerontology 60: 49–55.

Lim PO, Kim HJ and Nam HG (2007) Leaf senescence. Annual Review of Plant Biology 58: 115–136.

Thomas H, Ougham H, Wagstaff C and Stead A (2003) Defining senescence and cell death. Journal of Experimental Botany 54: 1127–1132.

Woo HR, Koo HJ, Kim J, et al. (2016) Programming of plant leaf senescence with temporal and inter‐organellar coordination of transcriptome in Arabidopsis. Plant Physiology 171: 452–467.

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How to Cite close
McCabe, Paul(Mar 2017) Senescence in Plants. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0020133.pub2]