Logo of transbhomepageaboutsubmitalertseditorial board
Philos Trans R Soc Lond B Biol Sci. 2002 Jun 29; 357(1422): 737–747.
PMCID: PMC1692983

The shoot apical meristem: the dynamics of a stable structure.


The shoot apical meristem (SAM) is a group of proliferating, embryonic-type cells that generates the aerial parts of the plant. SAMs are highly organized and stable structures that can function for years or even centuries. This is in apparent contradiction to the behaviour of their constituent cells, which continuously proliferate and differentiate. To reconcile the dynamic nature of the cells with the stability of the overall system the existence of elaborate signalling networks has been proposed. This is supported by recent work suggesting that the exchange of signals between cells, rather than a rigidly predetermined genetic program, is required for the establishment and functioning of an organized meristem. Together these interactions form a stable network, set up during embryogenesis, that assures the coordination of cell behaviour throughout development. Besides meristem-specific signalling cascades such as the CLAVATA receptor kinase pathway, which controls meristem size, these interactions involve plant hormones. In particular, cytokinins and auxins are implicated in the maintenance of meristem identity and phyllotaxis, respectively.

Full Text

The Full Text of this article is available as a PDF (506K).

Selected References

These references are in PubMed. This may not be the complete list of references from this article.
  • Aida M, Ishida T, Fukaki H, Fujisawa H, Tasaka M. Genes involved in organ separation in Arabidopsis: an analysis of the cup-shaped cotyledon mutant. Plant Cell. 1997 Jun;9(6):841–857. [PMC free article] [PubMed]
  • Aida M, Ishida T, Tasaka M. Shoot apical meristem and cotyledon formation during Arabidopsis embryogenesis: interaction among the CUP-SHAPED COTYLEDON and SHOOT MERISTEMLESS genes. Development. 1999 Apr;126(8):1563–1570. [PubMed]
  • Bartel Bonnie. AUXIN BIOSYNTHESIS. Annu Rev Plant Physiol Plant Mol Biol. 1997 Jun;48(NaN):51–66. [PubMed]
  • Benjamins R, Quint A, Weijers D, Hooykaas P, Offringa R. The PINOID protein kinase regulates organ development in Arabidopsis by enhancing polar auxin transport. Development. 2001 Oct;128(20):4057–4067. [PubMed]
  • Brand U, Fletcher JC, Hobe M, Meyerowitz EM, Simon R. Dependence of stem cell fate in Arabidopsis on a feedback loop regulated by CLV3 activity. Science. 2000 Jul 28;289(5479):617–619. [PubMed]
  • Byrne ME, Barley R, Curtis M, Arroyo JM, Dunham M, Hudson A, Martienssen RA. Asymmetric leaves1 mediates leaf patterning and stem cell function in Arabidopsis. Nature. 2000 Dec 21;408(6815):967–971. [PubMed]
  • Christensen SK, Dagenais N, Chory J, Weigel D. Regulation of auxin response by the protein kinase PINOID. Cell. 2000 Feb 18;100(4):469–478. [PubMed]
  • Chuck G, Lincoln C, Hake S. KNAT1 induces lobed leaves with ectopic meristems when overexpressed in Arabidopsis. Plant Cell. 1996 Aug;8(8):1277–1289. [PMC free article] [PubMed]
  • Clark SE, Running MP, Meyerowitz EM. CLAVATA1, a regulator of meristem and flower development in Arabidopsis. Development. 1993 Oct;119(2):397–418. [PubMed]
  • Clark SE, Williams RW, Meyerowitz EM. The CLAVATA1 gene encodes a putative receptor kinase that controls shoot and floral meristem size in Arabidopsis. Cell. 1997 May 16;89(4):575–585. [PubMed]
  • Elliott RC, Betzner AS, Huttner E, Oakes MP, Tucker WQ, Gerentes D, Perez P, Smyth DR. AINTEGUMENTA, an APETALA2-like gene of Arabidopsis with pleiotropic roles in ovule development and floral organ growth. Plant Cell. 1996 Feb;8(2):155–168. [PMC free article] [PubMed]
  • Estruch JJ, Chriqui D, Grossmann K, Schell J, Spena A. The plant oncogene rolC is responsible for the release of cytokinins from glucoside conjugates. EMBO J. 1991 Oct;10(10):2889–2895. [PMC free article] [PubMed]
  • Fisher RH, Barton MK, Cohen JD, Cooke TJ. Hormonal Studies of fass, an Arabidopsis Mutant That Is Altered in Organ Elongation. Plant Physiol. 1996 Apr;110(4):1109–1121. [PMC free article] [PubMed]
  • Fletcher JC, Brand U, Running MP, Simon R, Meyerowitz EM. Signaling of cell fate decisions by CLAVATA3 in Arabidopsis shoot meristems. Science. 1999 Mar 19;283(5409):1911–1914. [PubMed]
  • Gälweiler L, Guan C, Müller A, Wisman E, Mendgen K, Yephremov A, Palme K. Regulation of polar auxin transport by AtPIN1 in Arabidopsis vascular tissue. Science. 1998 Dec 18;282(5397):2226–2230. [PubMed]
  • Gutierrez-Cortines ME, Davies B. Beyond the ABCs: ternary complex formation in the control of floral organ identity. Trends Plant Sci. 2000 Nov;5(11):471–476. [PubMed]
  • Hake S. Transcription factors on the move. Trends Genet. 2001 Jan;17(1):2–3. [PubMed]
  • Hake S, Char BR, Chuck G, Foster T, Long J, Jackson D. Homeobox genes in the functioning of plant meristems. Philos Trans R Soc Lond B Biol Sci. 1995 Oct 30;350(1331):45–51. [PubMed]
  • Hernandez LF, Green PB. Transductions for the Expression of Structural Pattern: Analysis in Sunflower. Plant Cell. 1993 Dec;5(12):1725–1738. [PMC free article] [PubMed]
  • Irish VF. Patterning the flower. Dev Biol. 1999 May 15;209(2):211–220. [PubMed]
  • Ishida T, Aida M, Takada S, Tasaka M. Involvement of CUP-SHAPED COTYLEDON genes in gynoecium and ovule development in Arabidopsis thaliana. Plant Cell Physiol. 2000 Jan;41(1):60–67. [PubMed]
  • Kappen C. Analysis of a complete homeobox gene repertoire: implications for the evolution of diversity. Proc Natl Acad Sci U S A. 2000 Apr 25;97(9):4481–4486. [PMC free article] [PubMed]
  • Kayes JM, Clark SE. CLAVATA2, a regulator of meristem and organ development in Arabidopsis. Development. 1998 Oct;125(19):3843–3851. [PubMed]
  • Kerstetter RA, Laudencia-Chingcuanco D, Smith LG, Hake S. Loss-of-function mutations in the maize homeobox gene, knotted1, are defective in shoot meristem maintenance. Development. 1997 Aug;124(16):3045–3054. [PubMed]
  • Klucher KM, Chow H, Reiser L, Fischer RL. The AINTEGUMENTA gene of Arabidopsis required for ovule and female gametophyte development is related to the floral homeotic gene APETALA2. Plant Cell. 1996 Feb;8(2):137–153. [PMC free article] [PubMed]
  • Laux T, Mayer KF, Berger J, Jürgens G. The WUSCHEL gene is required for shoot and floral meristem integrity in Arabidopsis. Development. 1996 Jan;122(1):87–96. [PubMed]
  • Li Y, Hagen G, Guilfoyle TJ. Altered morphology in transgenic tobacco plants that overproduce cytokinins in specific tissues and organs. Dev Biol. 1992 Oct;153(2):386–395. [PubMed]
  • Lincoln C, Long J, Yamaguchi J, Serikawa K, Hake S. A knotted1-like homeobox gene in Arabidopsis is expressed in the vegetative meristem and dramatically alters leaf morphology when overexpressed in transgenic plants. Plant Cell. 1994 Dec;6(12):1859–1876. [PMC free article] [PubMed]
  • Long JA, Barton MK. The development of apical embryonic pattern in Arabidopsis. Development. 1998 Aug;125(16):3027–3035. [PubMed]
  • Long JA, Moan EI, Medford JI, Barton MK. A member of the KNOTTED class of homeodomain proteins encoded by the STM gene of Arabidopsis. Nature. 1996 Jan 4;379(6560):66–69. [PubMed]
  • Lucas WJ, Bouché-Pillon S, Jackson DP, Nguyen L, Baker L, Ding B, Hake S. Selective trafficking of KNOTTED1 homeodomain protein and its mRNA through plasmodesmata. Science. 1995 Dec 22;270(5244):1980–1983. [PubMed]
  • Mayer KF, Schoof H, Haecker A, Lenhard M, Jürgens G, Laux T. Role of WUSCHEL in regulating stem cell fate in the Arabidopsis shoot meristem. Cell. 1998 Dec 11;95(6):805–815. [PubMed]
  • Mizukami Y, Fischer RL. Plant organ size control: AINTEGUMENTA regulates growth and cell numbers during organogenesis. Proc Natl Acad Sci U S A. 2000 Jan 18;97(2):942–947. [PMC free article] [PubMed]
  • Mok David WS, Mok Machteld C. CYTOKININ METABOLISM AND ACTION. Annu Rev Plant Physiol Plant Mol Biol. 2001 Jun;52(NaN):89–118. [PubMed]
  • Ng M, Yanofsky MF. Three ways to learn the ABCs. Curr Opin Plant Biol. 2000 Feb;3(1):47–52. [PubMed]
  • Okada K, Ueda J, Komaki MK, Bell CJ, Shimura Y. Requirement of the Auxin Polar Transport System in Early Stages of Arabidopsis Floral Bud Formation. Plant Cell. 1991 Jul;3(7):677–684. [PMC free article] [PubMed]
  • Ori N, Juarez MT, Jackson D, Yamaguchi J, Banowetz GM, Hake S. Leaf senescence is delayed in tobacco plants expressing the maize homeobox gene knotted1 under the control of a senescence-activated promoter. Plant Cell. 1999 Jun;11(6):1073–1080. [PMC free article] [PubMed]
  • Ori N, Eshed Y, Chuck G, Bowman JL, Hake S. Mechanisms that control knox gene expression in the Arabidopsis shoot. Development. 2000 Dec;127(24):5523–5532. [PubMed]
  • Pautot V, Dockx J, Hamant O, Kronenberger J, Grandjean O, Jublot D, Traas J. KNAT2: evidence for a link between knotted-like genes and carpel development. Plant Cell. 2001 Aug;13(8):1719–1734. [PMC free article] [PubMed]
  • Perbal MC, Haughn G, Saedler H, Schwarz-Sommer Z. Non-cell-autonomous function of the Antirrhinum floral homeotic proteins DEFICIENS and GLOBOSA is exerted by their polar cell-to-cell trafficking. Development. 1996 Nov;122(11):3433–3441. [PubMed]
  • Reinhardt D, Mandel T, Kuhlemeier C. Auxin regulates the initiation and radial position of plant lateral organs. Plant Cell. 2000 Apr;12(4):507–518. [PMC free article] [PubMed]
  • Rinne PL, van der Schoot C. Symplasmic fields in the tunica of the shoot apical meristem coordinate morphogenetic events. Development. 1998 Apr;125(8):1477–1485. [PubMed]
  • Riou-Khamlichi C, Huntley R, Jacqmard A, Murray JA. Cytokinin activation of Arabidopsis cell division through a D-type cyclin. Science. 1999 Mar 5;283(5407):1541–1544. [PubMed]
  • Rupp HM, Frank M, Werner T, Strnad M, Schmülling T. Increased steady state mRNA levels of the STM and KNAT1 homeobox genes in cytokinin overproducing Arabidopsis thaliana indicate a role for cytokinins in the shoot apical meristem. Plant J. 1999 Jun;18(5):557–563. [PubMed]
  • Sakamoto T, Kamiya N, Ueguchi-Tanaka M, Iwahori S, Matsuoka M. KNOX homeodomain protein directly suppresses the expression of a gibberellin biosynthetic gene in the tobacco shoot apical meristem. Genes Dev. 2001 Mar 1;15(5):581–590. [PMC free article] [PubMed]
  • Schneeberger R, Tsiantis M, Freeling M, Langdale JA. The rough sheath2 gene negatively regulates homeobox gene expression during maize leaf development. Development. 1998 Aug;125(15):2857–2865. [PubMed]
  • Schoof H, Lenhard M, Haecker A, Mayer KF, Jürgens G, Laux T. The stem cell population of Arabidopsis shoot meristems in maintained by a regulatory loop between the CLAVATA and WUSCHEL genes. Cell. 2000 Mar 17;100(6):635–644. [PubMed]
  • Semiarti E, Ueno Y, Tsukaya H, Iwakawa H, Machida C, Machida Y. The ASYMMETRIC LEAVES2 gene of Arabidopsis thaliana regulates formation of a symmetric lamina, establishment of venation and repression of meristem-related homeobox genes in leaves. Development. 2001 May;128(10):1771–1783. [PubMed]
  • Sessions A, Yanofsky MF, Weigel D. Cell-cell signaling and movement by the floral transcription factors LEAFY and APETALA1. Science. 2000 Aug 4;289(5480):779–782. [PubMed]
  • Sinha Neelima. LEAF DEVELOPMENT IN ANGIOSPERMS. Annu Rev Plant Physiol Plant Mol Biol. 1999 Jun;50(NaN):419–446. [PubMed]
  • Soni R, Carmichael JP, Shah ZH, Murray JA. A family of cyclin D homologs from plants differentially controlled by growth regulators and containing the conserved retinoblastoma protein interaction motif. Plant Cell. 1995 Jan;7(1):85–103. [PMC free article] [PubMed]
  • Souer E, van Houwelingen A, Kloos D, Mol J, Koes R. The no apical meristem gene of Petunia is required for pattern formation in embryos and flowers and is expressed at meristem and primordia boundaries. Cell. 1996 Apr 19;85(2):159–170. [PubMed]
  • Steinmann T, Geldner N, Grebe M, Mangold S, Jackson CL, Paris S, Gälweiler L, Palme K, Jürgens G. Coordinated polar localization of auxin efflux carrier PIN1 by GNOM ARF GEF. Science. 1999 Oct 8;286(5438):316–318. [PubMed]
  • Stone JM, Trotochaud AE, Walker JC, Clark SE. Control of meristem development by CLAVATA1 receptor kinase and kinase-associated protein phosphatase interactions . Plant Physiol. 1998 Aug;117(4):1217–1225. [PMC free article] [PubMed]
  • Szymkowiak Eugene J, Sussex Ian M. WHAT CHIMERAS CAN TELL US ABOUT PLANT DEVELOPMENT. Annu Rev Plant Physiol Plant Mol Biol. 1996 Jun;47(NaN):351–376. [PubMed]
  • Takada S, Hibara K, Ishida T, Tasaka M. The CUP-SHAPED COTYLEDON1 gene of Arabidopsis regulates shoot apical meristem formation. Development. 2001 Apr;128(7):1127–1135. [PubMed]
  • Tamaoki M, Kusaba S, Kano-Murakami Y, Matsuoka M. Ectopic expression of a tobacco homeobox gene, NTH15, dramatically alters leaf morphology and hormone levels in transgenic tobacco. Plant Cell Physiol. 1997 Aug;38(8):917–927. [PubMed]
  • Taylor CB. knox-on Effects on Leaf Development. Plant Cell. 1997 Dec;9(12):2101–2105. [PMC free article]
  • Timmermans MC, Hudson A, Becraft PW, Nelson T. ROUGH SHEATH2: a Myb protein that represses knox homeobox genes in maize lateral organ primordia. Science. 1999 Apr 2;284(5411):151–153. [PubMed]
  • Torres-Ruiz RA, Jürgens G. Mutations in the FASS gene uncouple pattern formation and morphogenesis in Arabidopsis development. Development. 1994 Oct;120(10):2967–2978. [PubMed]
  • Trotochaud AE, Hao T, Wu G, Yang Z, Clark SE. The CLAVATA1 receptor-like kinase requires CLAVATA3 for its assembly into a signaling complex that includes KAPP and a Rho-related protein. Plant Cell. 1999 Mar;11(3):393–406. [PMC free article] [PubMed]
  • Trotochaud AE, Jeong S, Clark SE. CLAVATA3, a multimeric ligand for the CLAVATA1 receptor-kinase. Science. 2000 Jul 28;289(5479):613–617. [PubMed]
  • van der Schoot C, Rinne P. Networks for shoot design. Trends Plant Sci. 1999 Jan;4(1):31–37. [PubMed]
  • Vernoux T, Kronenberger J, Grandjean O, Laufs P, Traas J. PIN-FORMED 1 regulates cell fate at the periphery of the shoot apical meristem. Development. 2000 Dec;127(23):5157–5165. [PubMed]
  • Vollbrecht E, Veit B, Sinha N, Hake S. The developmental gene Knotted-1 is a member of a maize homeobox gene family. Nature. 1991 Mar 21;350(6315):241–243. [PubMed]
  • Waites R, Selvadurai HR, Oliver IR, Hudson A. The PHANTASTICA gene encodes a MYB transcription factor involved in growth and dorsoventrality of lateral organs in Antirrhinum. Cell. 1998 May 29;93(5):779–789. [PubMed]
  • Weigel D. From floral induction to floral shape. Curr Opin Plant Biol. 1998 Feb;1(1):55–59. [PubMed]
  • Williams-Carrier RE, Lie YS, Hake S, Lemaux PG. Ectopic expression of the maize kn1 gene phenocopies the Hooded mutant of barley. Development. 1997 Oct;124(19):3737–3745. [PubMed]

Articles from Philosophical Transactions of the Royal Society B: Biological Sciences are provided here courtesy of The Royal Society


Save items

Related citations in PubMed

See reviews...See all...

Cited by other articles in PMC

See all...


  • MedGen
    Related information in MedGen
  • PubMed
    PubMed citations for these articles

Recent Activity

Your browsing activity is empty.

Activity recording is turned off.

Turn recording back on

See more...