Segments (Phytomers)


The structure of higher plants can be interpreted as being derived from a repetition of morphogenetic units called phytomers consisting of a leaf, a section of the stem, a lateral bud and – in grasses – adventitious roots. Such repetitive units of growth occur along the plant axis in a variety of forms with the potential for various phytomer components to be reduced, suppressed or modified. Particular phytomer variants are required, for example, to form specialized reproductive structures. The occurrence of phytomer variants that are typical for one part of a plant in other parts is called homoeosis and the study of such perturbations to the body plan of mutant plants provides promise for attempts to use molecular tools to trace the phytomer.

Keywords: plant structure; metamers; homeotic mutants; units of growth

Figure 1.

Arabidopsis thaliana seedling (immersed in water) showing blue sectors. These sectors are indicative of expression of the bacterial uid A reporter gene visualized by β‐glucuronidase (GUS) staining. On the left, one sector occupies part of the stem and terminates in the leaf above. This indicates the clonal relationship between this leaf and its subtending part of the stem (compare the ‘phytonic’ model sensu stricto). For details on the induction of these sectors see Bossinger and Smyth .

Figure 2.

The metameric structure of the barley plant. A to F designate six developmentally distinct regions: A, tiller region plus mesocotyl and coleoptile; B, culm; C, rachis; D, first‐order branch; E, rachilla; F, floret; a, stamen; c, collar; co, coleoptile; l, lodicule; le, lemma; n, neck; o, pistil; p, palea; pr, prophyll; sg, sterile glumes. Black boxes represent ‘phytomers type 2’ present at points of ramification. Reproduced with permission from Bossinger et al. .



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Further Reading

Bossinger G, Lundqvist U, Rohde W and Salamini F (1992) Genetics of plant development in barley. In: Munck L (ed.) Barley Genetics VI, vol. II, pp. 989–1022. Proceedings of the Sixth International Barley Genetics Symposium, July 22–27, 1991, Helsingborg, Sweden. Copenhagen: Munksgaard International.

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How to Cite close
Bossinger, Gerd(Mar 2009) Segments (Phytomers). In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0002093.pub2]