Stamens

Abstract

Stamens are the male reproductive organs of flowers. Typically, a stamen is made up of a pollen‐producing anther borne on a filament. Pollen arises in four sporogenous regions within the anther. The sporogenous cells are surrounded by nutritive support cells, the tapetum. Mature pollen is released from the anther by dehiscence of the anther wall. The developmental identity of the stamen is conferred by the combined action of MADS transcription factors. Subsequent cellular differentiation is under the control of a cascade of other transcription factor and signalling genes now being identified. Male sterility is useful in plant breeding, and may arise by loss‐of‐function of these genes, as well as by defects in mitochondria (cytoplasmic male sterility). Differences in the structure of stamens are associated with the types of pollinators involved. Stamens evolved from the microsporangia‐bearing organs of early seed plants.

Key Concepts:

  • Pollen is generated in stamens, the male reproductive organs of flowers.

  • Pollen arises from sporogenous cells within the anthers.

  • Sporogenous cells are surrounded by the tapetum, a nutritive layer of support cells.

  • Stamen identity is conferred by the action of MADS transcription factors controlling B, C and SEPALLATA function.

  • The transcription factor SPOROCYTELESS is required for generation of the sporogenous cells.

  • Other transcription factors and signalling kinases are required for the entire developmental cascade and are now being identified.

  • Mature pollen is released by dehiscence of the anther wall through slits called stomia.

  • The structure of stamens in a species is closely adapted to the specific pollinators involved for that species.

  • Pollen is also generated in nonflowering seed plants (gymnosperms and various extinct lineages), but it arises in leaf‐like organs (microsporophylls) rather than stamens.

Keywords: anther; cytoplasmic male sterility; dehiscence; pollen; pollination syndrome; tapetum

Figure 1.

Diagram of a typical stamen (e.g. the true lily, Lilium (Liliaceae)) at a stage when the pollen is maturing (after meiosis and before dehiscence). The stamen is made up of an anther (green) and a filament (white). The internal structure of the anther is shown in a transverse section. There are two thecae, each with two pollen sacs, separated by a connective (pale green). A vascular strand is present within the connective. Tissues within each pollen sac are, from the outside, the epidermis (dark yellow), a late‐forming endothecium with lignified thickening (orange), a middle layer (pale green), the nutritive tapetum (pink) and developing pollen grains (pale yellow). When pollen is mature, the two pollen sacs on each side will join and each theca will dehisce along a weakened region of the endothecium, the stomium.

Figure 2.

Developmental pathway leading to the generation of microspores and surrounding vegetative cells in a pollen sac of the anther. Archesporial cells arise between the outer epidermis and internal, undifferentiated cortical cells. The archesporial cells divide several times to generate outer primary parietal cells, and inner sporogenous cells that, in turn divide to generate secondary parietal cells and pollen mother cells, respectively. Meiosis occurs in the pollen mother cells (also known as microsporocytes), yielding microspores which separate and develop into pollen grains. The parietal cells differentiate into a layer of tapetal cells which envelops the spore cells providing nutrient and, later, components of the pollen wall. The parietal cells also generate an outer layer of endothecial cells which lie under the epidermis, and which are involved in anther dehiscence to release the mature pollen. An undifferentiated middle layer lies between the tapetum and endothecium. Several key Arabidopsis genes involved in controlling specific steps of cellular specialization are shown in red (see text). AG, AGAMOUS; BAM, BARELY ANY MERISTEM; DYT1, DYSFUNCTIONAL TAPETUM1; EMS1, EXCESS MICROSPOROCYTES1; SPL, SPOROCYTELESS and TPD1, TAPETAL DETERMINANT1.

Figure 3.

Flowers of Eucalyptus (Corymbia) ficifolia (Myrtaceae), each with many pigmented stamens that act to attract pollinators. Pigment is localized to the long filaments, each of which is capped by a tiny anther. The perianth (petals and sepals) occurs as a cap (buds on right) that falls off as the buds open.

close

References

Alves‐Ferreira M, Wellmer F, Banhara A et al. (2007) Global expression profiling applied to the analysis of Arabidopsis stamen development. Plant Physiology 145: 747–762.

Bowman JL, Smyth DR and Meyerowitz EM (1989) Genes directing flower development in Arabidopsis. Plant Cell 1: 37–52.

Canales C, Bhatt AM, Scott R and Dickinson H (2002) EXS, a putative LRR receptor kinase, regulates male germline cell number and tapetal identity and promotes seed development in Arabidopsis. Current Biology 12: 1718–1727.

Chase CD (2006) Cytoplasmic male sterility: a window to the world of plant mitochondrial‐nuclear interactions. Trends in Genetics 23: 81–90.

Endress PK and Doyle JA (2009) Reconstructing the ancestral angiosperm flower and its initital specializations. American Journal of Botany 96: 22–66.

Feng X and Dickinson HG (2007) Packaging the male germline in plants. Trends in Genetics 23: 503–510.

Frohlich MW and Chase MW (2007) After a dozen years of progress the origin of angiosperms is still a great mystery. Nature 450: 1184–1189.

Furness CA, Rudall PJ and Sampson FB (2002) Evolution of microsporogenesis in angiosperms. International Journal of Plant Sciences 163: 235–260.

Galliot C, Stuurman J and Kuhlemeier C (2006) The genetic dissection of pollination syndromes. Current Opinion in Plant Biology 9: 78–82.

Hanson MR and Bentolila S (2004) Interactions of mitochondrial and nuclear genes that affect male gametophyte development. Plant Cell 16: S154–S169.

Heslop‐Harrison J (1966) Cytoplasmic connections between angiosperm meiocytes. Annals of Botany 30: 221–230.

Honma T and Goto K (2001) Complexes of MADS‐box proteins are sufficient to convert leaves into floral organs. Nature 409: 525–529.

Hord CLH, Chen C, DeYoung BJ, Clark SE and Ma H (2006) The BAM1/BAM2 receptor‐like kinases are important regulators of Arabidopsis early anther development. Plant Cell 18: 1667–1680.

Ito T, Wellmer F, Yu H et al. (2004) The homeotic protein AGAMOUS controls microsporogenesis by regulation of SPOROCYTELESS. Nature 430: 356–360.

Jia G, Liu X, Owen HA and Zhao D (2008) Signaling and cell fate determination by the TPD1 small protein and EMS1 receptor kinase. Proceedings of the National Academy of Sciences of the USA 105: 2220–2225.

Keijzer CJ (1987) The process of anther dehiscence and pollen dispersal I. Opening mechanism of longitudinally dehiscing anthers. New Phytologist 105: 487–498.

Koltunow AM, Truettner J, Cox KH, Wallroth A and Goldberg RB (1990) Different temporal and spatial gene expression patterns occur during anther development. Plant Cell 2: 1201–1224.

Lohmann JU and Weigel D (2002) Building beauty: The genetic control of floral patterning. Developmental Cell 2: 135–142.

Mandaokar A, Thines B, Shin B et al. (2006) Transcriptional regulators of stamen development in Arabidopsis identified by transcriptional profiling. Plant Journal 46: 984–1008.

Ogawa M, Kay P, Wilson S and Swain SM (2009) ARABIDOPSIS DEHISCENCE ZONE POLYGALACTURONASE1 (ADPG1), ADPG2 and QUARTET2 are polygalacturonases required for cell separation during reproductive development in Arabidopsis. Plant Cell 21: 216–233.

Pacini E, Franchi GG and Hesse M (1985) The tapetum: its form, function and possible phylogeny in Embryophyta. Plant Systematics and Evolution 149: 155–185.

Pelaz S, Ditta G, Baumann E, Wisman E and Yanofsky MF (2000) B and C floral organ identity functions require SEPALLATA MADS‐box genes. Nature 405: 200–203.

Proctor M, Yeo P and Lack A (1996) The Natural History of Pollination. London: Harper Collins.

Sanders PM, Bui AQ, Weterings K et al. (1999) Anther developmental defects in Arabidopsis thaliana male‐sterile mutants. Sexual Plant Reproduction 11: 297–322.

Schiefthaler U, Balasubramanian S, Sieber P et al. (1999) Molecular analysis of NOZZLE, a gene involved in pattern formation and early sporogenesis during sex organ development in Arabidopsis thaliana. Proceedings of the National Academy of Sciences of the USA 96: 11664–11669.

Schopfer CR, Nasrallah ME and Nasrallah JB (1999) The male determinant of self‐incompatibility in Brassica. Science 286: 1697–1700.

Schwarz‐Sommer Z, Huijser P, Nacken W, Saedler H and Sommer H (1990) Genetic control of flower development by homeotic genes in Antirrhinum majus. Science 250: 931–936.

Scott RJ, Spielman M and Dickinson HG (2004) Stamen structure and function. Plant Cell 16: S46–S60.

Scott RJ, Spielman M and Dickinson HG (2006) Stamen development: Primordium to pollen. In: Jordan BR (ed.) The Molecular Biology and Biotechnology of Flowering, 2nd edn, pp. 298–330. Wallingford: CABI.

Sunström J and Egström P (2002) Conifer reproductive development involves B‐type MADS‐box genes with distinct and different activities in male organ primordia. Plant Journal 31: 161–169.

Theissen G and Becker A (2004) Gymnosperm orthologues of class B floral homeotic genes and their impact on understanding flower origin. Critical Reviews in Plant Science 23: 129–148.

Walker‐Larsen J and Harder LD (2000) The evolution of staminodes in angiosperms: patterns of stamen reduction, loss and functional re‐invention. American Journal of Botany 87: 1367–1384.

Wijeratne AJ, Zhang W, Sun Y et al. (2007) Differential gene expression in Arabidopsis wild‐type and mutant anthers: insights into anther cell differentiation and regulatory networks. Plant Journal 52: 14–29.

Wilson Z and Zhang D‐B (2009) From Arabidopsis to rice: pathways in pollen development. Journal of Experimental Botany 60: 1479–1492.

Yang SL, Xie LF, Mao HZ et al. (2003) TAPETUM DETERMINANT1 is required for cell specialization in the Arabidopsis anther. Plant Cell 15: 2792–2804.

Yang WC, Ye D, Xu J and Sundaresan V (1999) The SPOROCYTELESS gene of Arabidopsis is required for initiation of sporogenesis and encodes a nuclear protein. Genes & Development 13: 2108–2117.

Yanofsky MF, Ma H, Bowman JL et al. (1990) The protein encoded by the Arabidopsis homeotic gene agamous resembles transcription factors. Nature 346: 35–39.

Zhang P, Tan HTW, Pwee K‐H and Prakash PP (2004) Conservation of class C function of floral organ development during 300 million years of evolution from gymnosperms to angiosperms. Plant Journal 37: 566–577.

Zhang W, Sun Y, Timofejeva L et al. (2006) Regulation of Arabidopsis tapetum development and function by DYSFUNCTIONAL TAPETUM1 (DYT1) encoding a putative bHLH transcription factor. Development 133: 3083–3095.

Zhao D‐Z, Wang G‐F, Speal B and Ma H (2002) The EXCESS MICROSPOROCYTES1 gene encodes a putative leucine‐rich repeat receptor protein kinase that controls somatic and reproductive cell fates in the Arabidopsis anther. Genes & Development 16: 2021–2031.

Further Reading

Cresti M, Blackmore S and van Went JL (1992) Atlas of Sexual Reproduction in Flowering Plants. Berlin: Springer.

D'Arcy WG and Keating RC (eds) (1996) The Anther: Form, Function and Phylogeny. Cambridge: Cambridge University Press.

Endress PK (1994) Diversity and Evolutionary Biology of Tropical Flowers. Cambridge: Cambridge University Press.

Esau K (1977) Anatomy of Seed Plants, 2nd edn. New York: Wiley.

Faegri K and van der Pijl L (1979) The Principles of Pollination Ecology, 3rd edn. Oxford: Pergamon Press.

Glover BJ (2007) Understanding Flowers and Flowering an Integrated Approach. Oxford: Oxford University Press.

Goldberg RB, Beals TP and Sanders PM (1993) Anther development: basic principles and practical applications. Plant Cell 5: 1217–1229.

Ma H (2005) Molecular genetic analysis of microsporogenesis and microgametogenesis in flowering plants. Annual Review of Plant Biology 56: 393–434.

Smyth DR (2005) Morphogenesis of flowers: our evolving view. Plant Cell 17: 330–341.

Weberling F (1989) Morphology of Flowers and Inflorescences. Cambridge: Cambridge University Press.

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

* Required Field

How to Cite close
Smyth, David R(Jan 2010) Stamens. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0002066.pub2]