Xylem: Differentiation, Water Transport and Ecology


The xylem carries water from the roots to the leaves; it is also the major supporting tissue in large plants. Three major areas of current research are concerned with additional mechanisms for the ascent of water; patterning at the plant, tissue and cell levels and its molecular basis; and the ecological significance of xylem diversity.

Keywords: cohesion of water; comparative structure; ecological adaptations; pattern formation; plant hormones; auxin

Figure 1.

The dependence of xylem formed in regenerating cuttings on organ development and on auxin. (a) New xylem is orientated so it connects growing buds with new roots. Removal of a growing bud (on the right) stops differentiation. (b) Xylem is formed along tissue polarity even in the absence of root formation. A local source of the hormone auxin induces and orients xylem differentiation, replacing the effects of a growing bud.

Figure 2.

Double wounds orient new xylem at right angles to the original polarity of the stem, creating a new polar system. (a) An early stage may be the diffusion of auxin (either from the shoot above or exogenous) across the horizontal bridge. (b) Cells through which auxin passed gradually become polar and efficient auxin transporters, draining the auxin towards themselves. (c) This leads to the canalization of differentiation of new xylem. Its precise course appears to depend on chance.



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Further Reading

Baas P (1986) Ecological patterns of xylem anatomy. In: Givnish TJ (ed.) On the Economy of Plant Form and Function, pp. 327–352. Cambridge: Cambridge University Press.

Canny MJ (1998) Transporting water in plants. American Scientist 86: 152–159.

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Sachs T (1991) Pattern Formation in Plant Tissues. Cambridge: Cambridge University Press.

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Zimmermann MH (1983) Xylem Structure and the Ascent of Sap. Berlin: Springer‐Verlag.

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Sachs, Tsvi(Apr 2001) Xylem: Differentiation, Water Transport and Ecology. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1038/npg.els.0002076]