Oligogalacturonides enhance cytokinin-induced vegetative shoot formation in tobacco explants, inhibit polyamine biosynthetic gene expression, and promote long-term remobilisation of cell calcium

Abstract

Long-sized oligogalacturonides (OGs) are cell wall fragments that induce defence and developmental responses. The Ca(2+)-dependent "egg-box" conformation is required for their activity, and polyamines may prevent them from adopting this conformation. Although OGs are known to inhibit auxin-induced growth processes, their effect on cytokinin-induced ones requires investigation. In the present work OGs were shown to promote cytokinin (benzyladenine, BA)-induced vegetative shoot formation from tobacco leaf explants, independent of the presence of CaCl(2) in the medium and of auxin (indoleacetic acid, IAA) supply. The effect of polyamines, putrescine (PU) and spermidine (SD) supplied with/without their biosynthetic inhibitors (DFMO, CHA) was also investigated, and showed that spermidine enhanced adventitious vegetative shoot formation, but only on medium containing Ca(2+) and IAA. Treatments with inhibitors blocked this promotive effect. OGs did not alter free polyamine concentrations, but caused a moderate increase of conjugated ones, and exhibited an early inhibitory effect on polyamine biosynthetic gene expression. OGs, but not SD, caused long-term changes in calcium-associated epifluorescent signals in the cell walls, and, later, inside the cells of specific tissues. Electron microscopy analysis (ESI system) demonstrated that calcium accumulated in the cell walls and vacuoles of OG-cultured explants. The relationship between OGs, cytokinin, calcium, and polyamines in adventitious vegetative shoot formation is discussed.

The structure, function, and biosynthesis of plant cell wall pectic polysaccharides

“…For example, calcium-dependent induction of flowering shoot growth occurred in tobacco thin-cell layer explants when sycamore-derived OGAs of 12-14 residues in length were applied. 158,159 In addition, specific Arabidopsis apoplastic resident proteins were identified that may be affectors of the biological responses elicited by OGAs. 160 These proteins included a polygalacturonase-inhibiting protein, two lectins, an alpha-glucosidase, an alpha-xylosidase, and a leucine-rich repeat protein.…”

Pathogenicity of and plant immunity to soft rot pectobacteria

“…Thus, when focusing on the role of OGs in plant–pathogen interactions it is not possible, nor even desirable, to ignore the developmental role of OGs. As an example, the first observed development-related effect of exogenously applied OGs was an inhibition of auxin-induced stem elongation in peas (Branca et al, 1988), and since then further studies have solidified the role of OGs as having an antagonistic effect on auxin signaling and enhancing cytokinin-induced vegetative shoot formation (Falasca et al, 2008). Clarifying the mechanistics behind this antagonistic role to auxin could provide a fruitful approach in elucidating the detailed role of OGs in plant–pathogen interactions (Savatin et al, 2011; Qi et al, 2012).…”

Plant Cell Wall Polymers: Function, Structure and Biological Activity of Their Derivatives

“…Calcium may also directly interact with long-sized OGAs promoting the formation of structures with an "egg-box" conformation, which may potentiate their biological activity [56]. Nevertheless the promotion of vegetative shoot formation in Nicotiana tabacum explants has been observed to be independent of exogenous Ca 2+ [57].…”