Roots and Root Systems

Abstract

Roots, together with stems and leaves, constitute the major organs of vascular plants. The main functions of the root system are to anchor and support the plant; to seek out, absorb and transport water and ions from the soil; and to transport and store the products of photosynthesis from the shoot system. Each root can be arbitrarily subdivided into several zones each with different functions: the apical zone of cell division, the source of all cells in the root; zone of cell elongation; zone of cell differentiation; zone of cell maturation. A root system is achieved by branchng of the primary root to produce one or more orders of lateral roots. Root hairs are epidermal enations that are functional in water and ion uptake and are an entry site for nitrogen‐fixing bacteria.

Key Concepts:

  • Roots, stems and leaves are the major organs of vascular plants.

  • Total extent of the root system usually greatly exceeds that of the shoot system.

  • The root apical meristem contains self‐perpetuating cells, now called stem cells, whose mitotic products differentiate into the cell types of the root.

  • Root tissues are arranged in concentric cylinders from the exterior inward are epidermis, cortex, endodermis, pericycle and vascular tissue consisting of alternating of bands of phloem and xylem.

  • Lateral roots are initiated in acropetal sequence from the pericycle tissue.

  • Adventitious roots are initiated in response to wounding or other environmental stimuli and disrupt the sequence of lateral root initiation.

  • Tropistic responses of roots to environmental stimuli such as gravitropism, phototropism, thigmotropism and hydrotropism are regulated by internally produced hormones such as auxin, ethylene and abscisic acid.

  • Root–microbial interactions result in formation of nitrogen‐fixing root nodules or mycorrhizal associations that are important in phosphorous uptake.

Keywords: acropetal; apical meristem; apoplastic; lateral root; pericycle; root hairs; root nodules; root specialisations; stem cells; tropism

Figure 1.

(a) Tap root system. Image from http://en.wikipedia.org/wiki/File:Plant_taproots.jpg. (b) Fibrous root system. Photo by Michael P Gadomski. http://db2.photoresearchers.com/search/7k1717. Reproduced with permission from Photo Researchers Inc.

Figure 2.

Longitudinal section of a root tip showing the distribution of cell types and zones. Copyright © Pearson Education Inc.

Figure 3.

Maize root types.

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References

Callaway RM and Mahall BE (2007) Family roots. Nature 448: 145–147.

Dinneny JR and Benfey PN (2009) Studying root development using a genomic approach In: Beeckman T (ed.) Annual Plant Reviews, Root Development, vol. 37, chap. 12, pp. 325–351. Oxford, UK: Blackwell.

Horn R, Yi K, Menand B et al. (2009) Root epidermal development in Arabidopsis. In: Beekman T (ed.) Root Development, chap. 3. Wiley‐Blackwell.

Matsuzaki Y, Ogawa‐Ohnishi M, Mori A et al. (2010) Secreted peptide signals required for maintenance of root stem cell niche in Arabidopsis. Science 329: 1065–1067.

Moreno‐Risueno MA et al. (2010) Oscillating gene expression determines competence for periodic Arabidopsis root branching. Science 329: 1306–1311.

Selosse M‐A and Rousset F (2011) The plant–fungal marketplace. Science 333: 828–829.

Further Reading

Beeckman T (2009) Annual Plant Reviews. In: Beekman T (ed.) Root Development, vol. 37. Oxford, UK: Wiley‐Blackwell.

Evert RF (2007) Esau's Plant Anatomy, 3rd edn. New Jersey: Wiley‐Interscience.

Howell SH (1998) Molecular Genetics of Plant Development. Cambridge: Cambridge University Press.

Steeves TA and Sussex IM (1989) Patterns in Plant Development, 2nd edn. Cambridge: Cambridge University Press.

Waisel Y, Eshel A and Kafkafi U (2002) Plant Roots: The Hidden Half, 3rd edn. New York: Marcel Dekker.

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How to Cite close
Kerk, Nancy M, and Sussex, Ian M(Apr 2012) Roots and Root Systems. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0002058.pub2]