A Secreted Factor Inducs Cell Expansion and Formation of Metaxylem-Like Tracheary Elements in Xylogenic Suspension Cultures of Zinnia

Abstract

Conditioned medium from mesophyll cell-suspension cultures of Zinnia eregans 1. has striking effects on cell expansion and tracheary element differentiation when applied to cultures of freshly isolated mesophyll cells. These effects include (a) induction of early cell expansion, (b) delay in differentiation by 48 h or more, (c) reduction in the synchrony of differentiation, and (d) early formation of very large, metaxylem-like tracheary elements. Like reduced osmotic potential and buffering at pH 5.5, conditioned medium appears to have its primary effect on cell expansion. Partia1 characterization of the expansion-inducing factor indicates that it is heat stable, of low molecular mass, and is resistant to protease. It also binds reversibly to concanavalin A but is not adsorbed by charcoal. We suggest that the secreted factor may be an oligosaccharide involved in the coordination of cell expansion and differentiation and the regulation of the protoxylem-like to metaxylem-like transition in xylogenic suspension cultures.In apical meristems cell expansion and cell differentiation are coordinated to give rise to highly organized tissues. For example, protoxylem TEs, which develop while surrounding cortical cells are expanding, deposit secondary cell walls in annular or helical patterns that allow the TEs to expand longitudinally in spite of the inelasticity of the secondary wall. As cell expansion ceases, developing metaxylem TEs deposit reticulate or pitted secondary cell walls that resist stretching and are also better able to withstand the pressure differential that develops between TEs and surrounding tissues during transpiration.Correlations between patterns of cell expansion and cell and tissue differentiation have been noted in differentiating culture systems, including embryogenic carrot (Daucus carota L.) cell-suspension cultures (van Engelen and de Vries, 1992), tobacco (Nicotiana tabacum L.) thin-layer cultures (Tran Thanh Van and Mutaftschiev, 1990), and xylogenic suspension cultures (Roberts and Haigler, 1994). In developing xylem the abundance of TEs (Torrey et al., 1971) and pattern of secondary-cell-wall deposition

Biosynthetic origin and longevity in vivo of α- d -mannopyranosyl-(1 → 4)-α- d -glucuronopyranosyl-(1 → 2)- myo -inositol, an unusual extracellular oligosaccharide produced by cultured rose cells

“…As an alternative, the spent medium of plant cell-suspension cultures can be collected in large volumes, facilitating the analysis of extraprotoplasmic oligosaccharides present at low concentration. Plant cell cultures have been shown to accumulate in the culture medium biologically relevant concentrations of certain oligosaccharins, including those derived from xyloglucans (Fry 1986), pectins (Tani et al 1992), Nlinked glycoproteins (Priem et al 1990;Priem and Gross 1992) and unidenti®ed sources (SchroÈ der and Knoop 1995; Roberts et al 1997). We are investigating the secretion of oligosaccharins by cultured Rosa cells (GarcõÂ a-Romera and Fry 1995Fry , 1997, and recently discovered in this source a novel trisaccharide, a-Dmannopyranosyl-(1 ® 4)-a-D-glucuronopyranosyl-(1 ® 2)-myo-inositol (MGI) (Smith et al 1999).…”

Progress of Lignification Mediated by Intercellular Transportation of Monolignols During Tracheary Element Differentiation of Isolated Zinnia Mesophyll Cells

“…In addition to these hormones, several factors have been shown to be involved in intercellular interactions during TE differentiation. An oligosaccharide-like secreted factor in Zinnia conditioned medium appeared to play an important role in cell expansion and metaxylem-like TE differentiation (Roberts et al 1997). Phytosulfokine-a secreted into Zinnia conditioned medium was suggested to be a factor responsible for TE differentiation (Matsubayashi et al 1999).…”

Galactoglucomannans Increase Cell Population Density and Alter the Protoxylem/Metaxylem Tracheary Element Ratio in Xylogenic Cultures of Zinnia

“…Moreover, Figure 4C revealed that MX differentiation may occur without an increase in cell volume, whereas mesophyll cells that undergo cell expansion may differentiate into PX. Thus, cell expansion and MX differentiation are not always intimately linked as previously described (Roberts et al, 1997;Pesquet et al, 2005).…”

“…These results suggest that mannans may be naturally occurring signaling molecules involved in TE differentiation. Moreover, an expansion-inducing factor, originally described as a secreted oligosaccharide, has been partially characterized from conditioned culture medium from 6-d-old zinnia cultures (Roberts et al, 1997). When expansion-inducing factor was added to fresh cultures, early production of MX was observed, providing further evidence that oligosaccharide signaling occurs in xylogenic zinnia cultures.…”

“…The polypeptide backbone of the xylogen is a hybrid-type molecule with properties of both arabinogalactan proteins and nonspecific lipid transfer proteins (Motose et al, 2004). Second, a putative oligosaccharide secreted during TE differentiation in zinnia cultures was shown to regulate the PX-MX transition (Roberts et al, 1997).…”