Phloem transdifferentiation from immature xylem cells during bark regeneration after girdling in Eucommia ulmoides Oliv

Abstract

Eucommia ulmoides Oliv. (Eucommiaceae), a traditional Chinese medicinal plant, was used to study phloem cell differentiation during bark regeneration after girdling on a large scale. Here it is shown that new sieve elements (SEs) appeared in the regenerated tissues before the formation of wound cambium during bark regeneration after girdling, and they could originate from the transdifferentiation of immature/differentiating axial xylem cells left on the trunk. Assays of water-cultured twigs revealed that girdling blocked sucrose transport until the formation of new SEs, and the regeneration of the functional SEs was not dependent on the substance provided by the axis system outside the girdled areas, while exogenous indole acetic acid (IAA) applied on the wound surface accelerated SE differentiation. The experiments suggest that the immature xylem cells can transdifferentiate into phloem cells under certain conditions, which means xylem and phloem cells might share some identical features at the beginning of their differentiation pathway. This study also showed that the bark regeneration system could provide a novel method for studying xylem and phloem cell differentiation.

Vascular Cell Induction Culture System Using Arabidopsis Leaves (VISUAL) Reveals the Sequential Differentiation of Sieve Element-Like Cells

“…Calli culture sometimes induces ectopic formation of SE-like cells in several plant species (Wetmore and Rier, 1963;Aloni, 1980;reviewed in Sjolund, 1997). Regeneration of phloem tissues after bark girdling has also been used to study phloem differentiation (Pang et al, 2008). VISUAL has several advantages beyond these conventional methods.…”

VASCULAR-RELATED NAC-DOMAIN6 and VASCULAR-RELATED NAC-DOMAIN7 Effectively Induce Transdifferentiation into Xylem Vessel Elements under Control of an Induction System

“…In general, for further analysis of the molecular mechanisms underlying cell differentiation processes, in vitro inducible systems are fruitful because of its high-synchronous differentiation (Fukuda, 1997;Roberts and McCann, 2000;McCurdy et al, 2008;Pang et al, 2008). One well-investigated system for in vitro xylem vessel element differentiation is the induction system using isolated mesophyll cells from Zinnia elegans (Fukuda, 1997).…”

Structural and functional heterogeneity in phloem loading and transport

“…When APL is ectopically expressed throughout the vascular core, the protein represses xylem differentiation and induces phloem-like characteristics in the xylem tissue (Bonke et al, 2003; Carlsbecker and Helariutta, 2005). It has also been shown that immature xylem cells can transdifferentiate into phloem during bark regeneration in trees (Pang et al, 2008). Given the interplay between phloem and xylem differentiation (Carlsbecker and Helariutta, 2005; Miyashima et al, 2013), it is tempting to speculate that intermediates between both vascular identities could arise, leading to rapid diversity in both structure and physiology.…”