Shoots and Buds in Arabidopsis

Abstract

The shoot is the above‐ground part of higher plants. To produce new shoot tissue, repetitive organ formation takes place at the tip of shoots and in floral buds by the activity of stem cell systems, called shoot and flower meristems. The shoot meristem is set up during embryogenesis and, after seedling germination, produces leaves, stems and eventually flowers. One of the key issues of the shoot meristem is to maintain a balance between cell proliferation and differentiation. A complex set of genetic and hormonal regulation ensures the maintenance of undifferentiated cells in the centre of the shoot meristem and the initiation of organ primordia at its flanks. While shoot meristems are indeterminate structures, in flower meristems stem cell maintenance ceases once the floral organs have been generated.

Key Concepts:

  • The shoot apical meristem produces the above‐ground organs of plants.

  • Stem cells located in the centre of the shoot meristem are maintained by a self‐regulatory gene expression network involving the WUSCHEL and CLAVATA genes.

  • Cytokinins play a role in meristem cell proliferation and in stem cell positioning.

  • Auxin is essential for organ primordia formation.

  • The shoot meristem is established during plant embryogenesis.

  • In floral meristems, stem cells are only maintained for a limited time.

Keywords: development; plant development; shoot meristem; stem cells; embryogenesis; flowering time

Figure 1.

Shoot meristem homeostasis. The stem cells (SC) are specified by yet unidentified signalling from the underlying WUS‐expressing organising centre (OC). Stem cells in turn negatively regulate the size of the OC. Cells that exit the stem cell region initiate differentiation and are recruited into organ primordia. RZ, rib zone; PZ, peripheral zone; CZ, central zone; L1, layer 1.

Figure 2.

Initiation of the shoot meristem. The shoot meristem is initiated early in embryo development as indicated by the onset of WUS expression. STM expression starts at globular stage, CLV3 expression when cotyledons (C) grow out. VP, vascular primordium.

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Further Reading

Besnard F, Vernoux T and Hamant O (2011) Organogenesis from stem cells in planta: multiple feedback loops integrating molecular and mechanical signals. Cellular and Molecular Life Sciences: CMLS 68(17): 2885–2906.

Dodsworth S (2009) A diverse and intricate signalling network regulates stem cell fate in the shoot apical meristem. Developmental Biology 336(1): 1–9.

Ha CM, Jun JH and Fletcher JC (2010) Shoot apical meristem form and function. Current Topics in Developmental Biology 91: 103–140.

Jenik PD, Gillmor CS and Lukowitz W (2007) Embryonic patterning in Arabidopsis thaliana. Annual Review of Cell and Developmental Biology 23: 207–236.

Rieu I and Laux T (2009) Signaling pathways maintaining stem cells at the plant shoot apex. Seminars in Cell & Developmental Biology 20(9): 1083–1088.

Sablowski R (2007) Flowering and determinacy in Arabidopsis. Journal of Experimental Botany 58(5): 899–907.

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Truernit, Elisabeth(May 2012) Shoots and Buds in Arabidopsis. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0002054.pub2]