A central feature of plant development is the continuous generation of organs throughout the lifespan of the plant. In the region designated the meristem, undifferentiated cells are maintained throughout the life cycle of the plant, providing a source of cells from which plant organs are derived. Cells that are differentiating as they are channelled toward a particular developmental fate also reside in the meristem, as do the resultant organ primordia. The meristem is a self‐renewing structure and its stem cell population is maintained at a near constant number despite the perpetual mobilisation of differentiating cells into organogenesis. The meristem's capacity to balance continuous differentiation of cells while replenishing the pool of undifferentiated, pluripotent cells is tightly controlled by a very complex and overlapping network of regulatory pathways.

Key Concepts:

  • Plants, unlike animals, have the capacity to generate new organs post‐embryonically, throughout the lifespan of the plant.

  • Shoot and root apical meristems have the capacity to balance perpetual differentiation of cells while maintaining a population of undifferentiated stem cells.

  • Because fates of meristematic cells are determined by their relative positions, they must be in continuous communication with their neighbouring cells.

  • Signals can be transmitted from more mature cells to initial cells to specify the pattern of meristem differentiation.

  • The number of stem cells in meristems is remarkably constant despite the continuous recruitment of differentiating cells into organs.

  • In Arabidopsis shoot meristems, a feedback loop between WUSCHEL and the CLAVATA signalling pathway is crucial for specifying and maintaining the stem cell niche in the shoot apex.

  • Within their niche boundaries, stem cells remain in an undifferentiated state in response to positional cues from neighbouring cells while cells displaced from the niche begin the process of differentiation.

Keywords: development; differentiation; primordium; shoot apex; stem cells; meristem

Figure 1.

The dynamics of shoot meristem development. (a) A single undifferentiated cell (box) in the (CZ). All the cells in (b) and (c) are derived from this cell. (b) The progeny cells (circles) in the (PZ) are channelled toward a particular developmental fate. (c) Cells are increasingly displaced from the centre of the meristem and incorporated into organ primordia (closed circles). RM, rib meristem.

Figure 2.

Apical meristems differ across the plant kingdom. (a) The meristem of red algae consisting of a single (AC). (b) The meristem of a gymnosperm, pine. The central dome‐like structure is the meristem and it is flanked by (OP), which in turn are flanked by organs in the outermost regions. (c) The meristem of maize. The dark tissue indicates the region of KNOTTED expression. KNOTTED in maize, and its counterpart, SHOOTMERISTEMLESS, in Arabidopsis, are essential for maintenance of a population of undifferentiated cells in the meristem. (d) The meristem of an angiosperm, Arabidopsis. The central dome‐like structure is the meristem, and it is flanked by organ primordia.



Aida M, Beis D and Hiedstra R (2004) The PLETHORA genes mediate patterning of the Arabidopsis root stem cell niche. Cell 119: 109–120.

Barton MK and Poethig RS (1993) Formation of the shoot apical meristem in Arabidopsis thaliana: an analysis of development in the wildtype and shoot meristemless mutant. Development 119: 823–831.

Benkova E, Michniewicz M, Sauer M et al. (2003) Local, efflux‐dependent auxin gradients as a common module for plant organ formation. Cell 115: 591–602.

van den Berg C, Willemsen V, Hage W, Weisbeek P and Scheres B (1995) Cell fate in the Arabidopsis root meristem determined by directional signalling. Nature 378: 62–65.

Berger F, Hasselhoff J, Scheifelbein J and Dolan L (1998) Positional information in root epidermis is defined during embryogenesis and acts in domains with strict boundaries. Current Biology 8: 421–430.

Bleckmann A, Weidtkamp‐Peters S, Seidel CAM and Simon R (2010) Stem cell signaling in Arabidopsis requires CRN to localize CLV2 to the plasma membrane. Plant Physiology 152: 166–176.

Brand U, Fletcher JC, Hobe M, Meyerowitz EM and Simon R (2000) Dependence of stem cell fate in Arabidopsis on a feedback loop regulated by CLV3 activity. Science 289: 617–619.

Clark SE, Jacobsen SE, Levin JZ and Meyerowitz EM (1996) The CLAVATA and SHOOT MERISTEMLESS loci competitively regulate meristem activity in Arabidopsis. Development 122: 1567–1575.

Clark SE, Running MP and Mayerowitz EM (1993) CLAVATA1, a regulator of meristem and flower development in Arabidopsis. Development 119: 397–418.

Clark SE, Running MP and Mayerowitz EM (1995) CLAVATA3 is a specific regulator of shoot and floral meristem development affecting the same process as CLAVATA1. Development 121: 2057–2067.

Clark SE, Williams RW and Meyerowitz EM (1997) The CLAVATA1 gene encodes a putative receptor kinase that controls shoot and floral meristem size in Arabidopsis. Cell 89: 575–585.

Dawe RK and Freeling M (1990) Clonal analysis of the cell lineages in the male flower of maize. Developmental Biology 142: 233–245.

Endrizzi K, Moussain B, Haecker A, Levin JZ and Laux T (1996) The SHOOT MERISTEMLESS gene is required for maintenance of undifferentiated cells in Arabidopisis shoot and floral meristems and acts at a different regulatory level than the meristem genes WUSCHEL and ZWILLE. Plant Journal 10: 967–979.

Epel BL (1994) Plasmodesmata: composition, structure and trafficking. Plant Molecular Biology 26(5): 1343–1356.

Fleming AJ, McQueen‐Mason S, Mandel T and Kuhlemeier C (1997) Induction of leaf primordia by the cell wall protein expansin. Science 276: 1415–1418.

Fletcher JC, Brand U, Running MP, Simon R and Meyerowitz EM (1999) Signaling of cell fate decisions by CLAVATA3 in Arabidopsis shoot meristems. Science 283: 1911–1914.

Furner IJ and Pumfrey JE (1992) Cell fate in the shoot apical meristem of Arabidopsis thaliana. Development 115: 755–764.

Galinha C, Hofhuis H, Luijten M et al. (2007) PLETHORA proteins as dose‐dependent master regulators of Arabidopsis root development. Nature 449: 1053–1057.

Green PB (1999) Expression of pattern in plants: combining molecular and calculus‐based biophysical paradigms. American Journal of Botany 86: 1059–1076.

Hamant O, Heisler MG, Jonsson H et al. (2008) Developmental patterning by mechanical signals in Arabidopsis. Science 322: 1650–1655.

Heisler MG, Hamant O, Krupinski P et al. (2010) Alignment between PIN1 polarity and microtubule orientation in the shoot apical meristem reveals a tight coupling between morphogenesis and auxin transport. PLoS Biology 8(10).

Heisler MG, Ohno C, Das P et al. (2005) Patterns of auxin transport and gene expression during primordium development revealed by live imaging of the Arabidopsis inflorescence meristem. Current Biology 15: 1899–1911.

Hernandez LF and Green PB (1993) Transductions for the expression of structural pattern: analysis in sunflower. Plant Cell 5: 1725–1738.

Irish VF and Sussex JM (1992) A fate map of the Arabidopsis embryonic shoot apical meristem. Development 115: 745–753.

Jeong S, Trotochaud AE and Clark SE (1999) The Arabidopsis CLAVATA2 gene encodes a receptor‐like protein required for the stability of the CLAVATA1 receptor‐ like kinase. Plant Cell 11: 1925–1934.

Jonsson H, Heisler MG, Shapiro BE, Mjolsness E and Meyerowitz EM (2006) An auxin‐driven polarized transport model for phyllotaxis. Proceedings of the National Academy of Sciences of the USA 103: 1633–1638.

Kim JY, Rim Y, Wang J and Jackson D (2005) A novel cell‐to‐cell trafficking assay indicates that the KNOX homeodomain is necessary and sufficient for intercellular protein and mRNA trafficking. Genes & Development 19: 788–793.

Kim JY, Yuan Z, Cilia M, Khalfan‐Jagani Z and Jackson D (2002) Intercellular trafficking of a KNOTTED1 green fluorescent protein fusion in the leaf and shoot meristem of Arabidopsis. Proceedings of the National Academy of Sciences of the USA 99: 4103–4108.

Klar AJ (2002) Plant mathematics: Fibonacci's flowers. Nature 417: 595.

Kuhlemeier C (2007) Phyllotaxis. Trends in Plant Science 12: 143–150.

Laux T, Mayer KF, Berger J and Jurgens G (1996) The WUSCHEL gene is required for shoot and floral meristem integrity in Arabidopsis. Development 122: 87–96.

Leibfried A, To JP, Busch W et al. (2005) WUSCHEL controls meristem function by direct regulation of cytokinin‐inducible response regulators. Nature 438: 1172–1175.

Lenhard M, Jurgens G and Laux T (2002) The WUSCHEL and SHOOTMERISTEMLESS genes fulfill complementary roles in Arabidopsis shoot meristem regulation. Development 129: 3195–3206.

Lenhard M and Laux T (2003) Stem cell homeostasis in the Arabidopsis shoot meristem is regulated by intercellular movement of CLAVATA3 and its sequestration by CLAVATA1. Development 130: 3163–3173.

Leyser HMO and Furner IJ (1992) Characterisation of three shoot apical meristem mutants of Arabidopsis thaliana. Development 116: 397–403.

Long JA, Moan EI, Medford JI and Barton MK (1996) A member of the KNOTTED class of homeodomain proteins encoded by the STM gene of Arabidopsis. Nature 379: 66–69.

Lucas WJ, Bouche‐Pillon S, Jackson DP et al. (1995) Selective trafficking of KNOTTED1 homeodomain protein and its mRNA through plasmodesmata. Science 270: 1980–1983.

Lyndon RF (1998) The Shoot Apical Meristem: Its Growth and Development. New York: Cambridge University Press.

Mayer KF, Schoof H, Haecker A et al. (1998) Role of WUSCHEL in regulating stem cell fate in the Arabidopsis shoot meristem. Cell 95: 805–815.

Medford JI, Behringer FJ, Callos JD and Feldman KA (1992) Normal and abnormal development in the Arabidopsis vegetative shoot apex. Plant Cell 4: 631–643.

Mitchison GJ (1977) Phyllotaxis and Fibonacci series. Science 196: 270–275.

Mueller R, Bleckmann A and Simon R (2008) The Receptor Kinase CORYNE of Arabidopsis Transmits the Stem Cell–Limiting Signal CLAVATA3 Independently of CLAVATA1. The Plant Cell 20: 934–946.

Muller R, Borghi L, Kwiatkowska D, Laufs P and Simon R (2006) Dynamic and compensatory responses of Arabidopsis shoot and floral meristems to CLV3 signaling. Plant Cell 18: 1188–1198.

Ogawa M, Shinohara H, Sakagami Y and Matsubayashi Y (2008) Arabidopsis CLV3 peptide directly binds CLV1 ectodomain. Science 319: 294.

Ohyama K, Shinohara H, Ogawa‐Ohnishi M and Matsubayashi Y (2009) A glycopeptide regulating stem cell fate in Arabidopsis thaliana. Nature Chemical Biology 5: 578–580.

Petrasek J, Mravec J, Bouchard R et al. (2006) PIN proteins perform a rate‐limiting function in cellular auxin efflux. Science 312: 914–918.

Poethig RS (1987) Clonal analysis of cell lineage patterns in plant development. American Journal of Botany 74: 581–594.

Reddy GV and Meyerowitz EM (2005) Stem‐cell homeostasis and growth dynamics can be uncoupled in the Arabidopsis shoot apex. Science 310: 663–667.

Reinhardt D, Frenz M, Mandel T and Kuhlemeier C (2003a) Microsurgical and laser ablation analysis of interactions between the zones and layers of the tomato shoot apical meristem. Development 130: 4073–4083.

Reinhardt D, Mandel T and Kuhlemeier C (2000) Auxin regulates the initiation and radial position of plant lateral organs. Plant Cell 12: 507–518.

Reinhardt D, Pesce ER, Stieger P et al. (2003b) Regulation of phyllotaxis by polar auxin transport. Nature 426: 255–260.

Satina S, Blakeslee AF and Avery AG (1940) Demonstration of the three germ layers in the shoot apex of Datura by means of induced polyploidy in periclinal chimeras. American Journal of Botany 27: 895–905.

Schoof H, Lenhard M, Haecker A et al. (2000) The stem cell population of Arabidopsis shoot meristems is maintained by a regulatory loop between the CLAVATA and WUSCHEL genes. Cell 100: 635–644.

Selker JM and Green PB (1984) Organogenesis in Graptopetalum paraguayense E. Walther: shifts in orientation of cortical microtubule arrays are associated with periclinal divisions. Plant 160(4): 289–297.

Selker JM, Steucek GL and Green PB (1992) Biophysical mechanisms for morphogenetic progressions at the shoot apex. Developmental Biology 153(1): 29–43.

Stahl Y, Wink RH, Ingram GC and Simon R (2009) A signaling module controlling the stem cell niche in Arabidopsis root meristems. Current Biology 19(11): 909–914.

Steeves T and Sussex I (1989) Patterns in Plant Development. Cambridge, UK: Cambridge University Press.

Stewart RN and Dermen H (1975) Flexibility in ontogeny as shown by contribution of shoot apical layers to leaves of periclinal chimeras. American Journal of Botany 62: 935–947.

Stone JM, Trotochaud AE, Walker JC and Clark SE (1998) Control of meristem development by CLAVATA1 receptor kinase and kinase‐associated protein phosphatase interactions. Plant Physiology 117: 1217–1225.

Tilney‐Bassett RAE (1986) Plant Chimeras. Baltimore: Edward Arnold.

Veit B (2009) Hormone mediated regulation of the shoot apical meristem. Plant Molecular Biology 69: 397–408.

Wildwater M, Campilho A, Perez‐Perez JM et al. (2005) The RETINOBLASTOMA‐related gene regulates stem cell maintenance in Arabidopsis roots. Cell 123(7): 1337–1349.

Further Reading

Bennett T and Scheres B (2010) Root development‐two meristems for the price of one? Current Topics in Developmental Biology 91: 67–102.

Barton MK (2010) Twenty years on: the inner workings of the shoot apical meristem, a deveopmental dynamo. Developmental Biology 341(1): 95–113.

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

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

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

Stahl Y and Simon R (2010) Plant primary meristems: shared functions and regulatory mechanisms. Current Opinion in Plant Biology 13: 53–58.

Tucker MR and Laux T (2007) Connecting the paths in plant stem cell regulation. Trends in Cell Biology 17(8): 403–410.

Contact Editor close
Submit a note to the editor about this article by filling in the form below.

* Required Field

How to Cite close
Green, Kirsten A(Jun 2012) Meristems. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0002049.pub2]