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.

Formation of plant tracheary elements in vitro – a review

“…It is a cost-effective and renewable resource for industry and energy demands. The understanding of the underlying processes of wood formation (xylogenesis) is imperative for improving the quantity and quality of wood produced considering the important roles of wood currently and in the future (Bollhöner et al 2012;Oda and Fukuda 2012;Fukuda 2010;Turner et al 2007). …”

“…Trachearyelement differentiation is characterised by a series of cytological changes. Initial cell expansion is followed by deposition of lignified secondary cell wall and ultimately programmed cell death (PCD) (Fukuda 1996(Fukuda , 1997b(Fukuda , 2010McCann 1997), the latter including autolysis of the cellular contents (Denton et al 2012;Kuriyama and …”