Plant Tracheary Elements

Abstract

The plant tracheary element is the constituent of vessels and tracheids. Tracheary elements are characterised by patterned secondary wall thickenings and programmed cell death (PCD) at maturity. Their differentiation is induced by plant hormones such as auxin, cytokinin and brassinosteroids, and suppressed by a small peptide, tracheary element differentiation inhibitory factor (TDIF), secreted from phloem cells. The final determination of tracheary element differentiation is initiated by master transcription factors, VAD6 and VND7 (vascular‐related NAC‐domain 7). The secondary wall pattern is formed by guiding the movement of cellulose synthase complex in the plasma membrane by the cortical microtubules. The PCD during tracheary element differentiation is initiated by the rupture of the central vacuole in which cell death‐related hydrolytic enzymes have been accumulated. Thus the process of tracheary element differentiation is well understood, so that tracheary element differentiation is an excellent model of cell differentiation in plants.

Key Concepts:

  • The xylem, which is tissue specific to the vascular plants, is composed of tracheary elements (TEs), parenchyma cells and fibres.

  • Procambial cells produce the primary xylem containing protoxylem and metaxylem TEs in planta.

  • Typical characteristics of TEs are patterned secondary wall thickenings and programmed cell death (PCD).

  • TE differentiation is regulated by plant hormones such as auxin, cytokinin and brassinosteroids.

  • A small peptide secreted from phloem cells prevents procambial cells from differentiating into TEs.

  • VND6 and VND7 are master transcription factors that initiate TE differentiation.

  • Microtubules determine the secondary wall pattern by guiding the movement of cellulose synthase complex in the plasma membrane.

  • During the formation of secondary walls, levels of cellulose and hemicellulose increase and the deposition of pectin ceases, and a little later lignin deposition starts.

  • The central vacuole plays a crucial role in TE PCD.

  • A Zinnia xylogenic culture is an excellent model system of TE differentiation.

Keywords: auxin; brassinosteroids; cell communication; cytokinin; master transcription factors; procambium; programmed cell death; secondary cell walls; xylem; Zinnia

Figure 1.

A single TE that is being differentiated from a single Zinnia mesophyll cell.

Figure 2.

TEs formed ectopically in epidermal tissue by over‐expression of VND7. This picture is taken by M Yamaguchi and T Demura.

Figure 3.

An illustration showing that cortical microtubules control the position and orientation of secondary wall thickenings. This is drawn by Y Oda.

Figure 4.

The process of TE differentiation in the Zinnia xylogenic culture. The initiation of differentiation occurs by a combination of auxin and cytokinin. The process of the in vitro TE differentiation is divided into three stages.

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How to Cite close
Fukuda, Hiroo(Sep 2010) Plant Tracheary Elements. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0001814.pub2]