Pectic Cell Wall Fragments Regulate Tobacco Thin-Cell-Layer Explant Morphogenesis.

Abstract

Pectic fragments of cell wall polysaccharides, released from the walls of suspension-cultured sycamore cells by treatment with endopolygalacturonase, were tested for morphogenesis-regulating activity in a modified tobacco thin-cell-layer explant (TCL) bioassay (D. Mohnen, S. Eberhard, V. Marfa, N. Doubrava, P. Toubart, D. J. Gollin, T.A. Gruber, W. Nuri, P. Albersheim, and A. Darvill, manuscript submitted). The pectic fragments inhibited the formation of roots on TCLs grown on a root-inducing medium containing 15 micromolar indole-3-butyric acid and 0.5 micromolar kinetin. Addition of the pectic fragments to a root-inducing medium containing 7 micromolar indole-3-butyric acid and 0.15 micromolar kinetin caused roots to form on the basal end of TCLs. TCLs cultured on this medium in the absence of added pectic fragments formed roots along their entire length. The pectic fragments induced polar tissue enlargement and the formation of flowers on TCLs cultured on transition medium. The flower-inducing activity was stable to heat treatment and proteolytic digestion. Pectic fragments isolated from the walls of suspension-cultured tobacco cells were as effective as those from the walls of sycamore cells in inducing de novo flower formation in the TCLs. These results support the hypothesis that oligosaccharins from plant cell walls regulate morphogenesis.

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

“…To date, there is limited information regarding their eVect on vegetative shoot formation in cultured explants. As reported by Eberhard et al (1989), pectic fragments, applied at 10 g l ¡1 to a medium containing 4 M indolebutyric acid and 0.5 M kinetin, inhibited root formation in tobacco thin cell layers, but induced the formation of a few Xoral or vegetative shoots. However, under diVerent hormonal conditions (1.5 M indolebutyric acid plus 0.8 M kinetin), the same pectic fragments supplied at various concentrations, including 10 g l ¡1 , enhanced the formation of Xowers, while leaving vegetative shoot formation poor.…”

“…In addition, OGs exhibit growth regulatory eVects on cell elongation (Branca et al 1988), on de novo Xower (Eberhard et al 1989;Marfà et al 1991), root (Bellincampi et al 1993(Bellincampi et al , 1996, and on stomata formation (Altamura et al 1998b) in cultured tobacco explants. To date, there is limited information regarding their eVect on vegetative shoot formation in cultured explants.…”

Subcellular localization and topology of homogalacturonan methyltransferase in suspension-cultured Nicotiana tabacum cells

“…Suspension-cultured tobacco (Nicotiana tabacum L. cv. Samsun) cells, originally isolated from pith callus tissue (Eberhard et al 1989), were grown on Murashige and Skoog (1962) medium supplemented with 4.5 lM 2,4-dichlorophenoxyacetic acid and 90 mM sucrose, and subcultured every 13±14 d (Doong et al 1995).…”

Differential elicitation of defense responses by pectic fragments in bean seedlings

“…In-vitro bioassays have con®rmed that pectic oligomers function as biological signals that stimulate a wide array of defence responses, ranging from early events at the cell surface to the subsequent biosynthesis of defence molecules such as phytoalexins, pathogenesis-related (PR) proteins, proteinase inhibitors, lignin (Coà te and Hahn 1994), and hydroxyprolinerich glycoproteins (Boudart et al 1995). In addition, it has been shown that these oligomers also regulate development and growth (Eberhard et al 1989;MarfaÁ et al 1991). Although active fragments are generally oligogalacturonides with a degree of polymerization (DP) of galacturonic acid (GalA) of 9±15, more-complex galacturonides can also act as elicitors (Brecht and Huber 1988).…”