Oxidized Oligogalacturonides Activate the Oxidation of Indoleacetic Acid by Peroxidase

Abstract

Partial hydrolysis of polygalacturonic acid with a purified a-1,4-endopolygalacturonase yielded oligogalacturonides and trace amounts of a series of modified oligogalacturonides. Three of the minor products were isolated and identified as oxidized oligogalacturonides possessing termini of galactaric acid. Oxidation of indole-3-acetic acid by peroxidases was activated by oxidized oligogalacturonides but not by normal analogs.Oligosaccharides composed of 1,4-linked a-D-galacturonic acid residues (oligogalacturonides) have been included in a possible new class of regulatory molecules consisting of plant cell wall fragments that have been named oligosaccharins (1).They act as elicitors for the accumulation ofproteinase inhibitors in tomato leaves (3) and of phytoalexins in several plants (6, 1 1). Evidence has been presented that oligogalacturonides of a specific Dp' regulate organ development in tobacco explants (14) and induce ethylene production in fruit tissues (5). There has not been an explanation of how these pectic fragments can induce such a variety of responses in plants. A clue to their mode of action may lie in a recent observation that certain anions are extraordinary activators of the oxidation of IAA by plant peroxidases (1 3). Mixtures of oligogalacturonides prepared by the controlled enzymic fragmentation of polygalacturonic acid also activate the oxidation of IAA, and this study deals with identification of the active components. MATERIALS AND METHODS Purification of PolygalacturonasesEndo-and exopolygalacturonases in Pectinase from Aspergillus niger (Sigma) were separated by chromatography on a column of Q-Sepharose (Pharmacia) and purified by fast protein liquid chromatography on a column of Mono Q (Pharmacia). Details of the purification and characterization of the enzymes will be published separately. A unit of exo-or endopolygalacturonase is defined as that amount liberating ,umol of reducing groups from polygalacturonic acid/min at 300C. ' Abbreviations: Dp, degree of polymerization; HPAE-PAD, high performance anion-exchange chromatography with pulsed amperometric detection; KnA, 1000 nanoamp. Preparation of Polygalacturonic Acid HydrolyzateTen grams of polygalacturonic acid (P3889, Sigma) was dissolved in 1 L water, adjusted to pH 4.5, and warmed to 30C. Endopolygalacturonase (280 units) was added to the solution and incubated at 30TC for 1 h. The enzyme was then inactivated by heating the solution at 1000C for 5 min and the small amount of precipitate was removed by centrifugation. The oligogalacturonides in the solution were precipitated by addition of 5 g CaCl2 and a volume of 95% ethanol at pH 6.0. The precipitate was collected by centrifugation, washed with 50% ethanol, and dried under vacuum. Analysis of Oligogalacturonides by High Performance Anion-Exchange ChromatographyOligogalacturonides were analyzed by HPAE-PAD on a CarboPac PAI column in a Dionex system. Elution was conducted with 0.19 M sodium acetate in 65 mm NaOH for 5 min and then with a linear gradient of 0.19 to...

Metabolic Responses to Heat Stress under Elevated Atmospheric CO2 Concentration in a Cool-season Grass Species

“…Threonic acid and glyceric acid have been reported to be sensitive to heat stress in many species, including arabidopsis (Kaplan et al, 2004), hybrid bermudagrass, and kentucky bluegrass (Du et al, 2011). Galactaric acid is derived from galacturonic acid by galacturonic acid oxidase, which has been found to stimulate the oxidation of indole acetic acid by peroxidase (Pressey, 1991) and acts as a substrate for galacturonic acid reductase leading to the synthesis of ascorbic acid. Sanchez et al (2008) reported that galactaric acid was decreased by salinity in arabidopsis.…”

Oligogalacturonide production upon Arabidopsis thaliana – Botrytis cinerea interaction

“…In B. cinerea-infected leaves, most PG products were converted into GalA 3 Me and GalA 2 ox. The production of the latter OGs presumably involved plant-produced OG oxidases (OGOX) (17,34,35) of the berberine bridge enzyme family. Oxidized OGs are more recalcitrant to the hydrolysis of fungal enzymes and, interestingly, plants overexpressing OGOX1 are more resistant to B. cinerea.…”

Oligosaccharins, brassinolides, and jasmonates: nontraditional regulators of plant growth, development, and gene expression.

“…TCLs will form roots, flowers, or vegetative shoots, depending on the auxin/cytokinin ratio (Mohnen et al, 1990). Oligogalacturonides can induce flower formation or inhibit root formation in tobacco TCLs or leaf explants (Eberhard et al, 1989;Mohnen et al, 1990;MarFa et al, 1991); they may act by interfering with auxin binding sites (LoSchiavo et al, 1991;Filippini et al, 1992) or by altering auxin metabolism (Pressey, 1991). However, little is known about the role of these pectic oligosaccharins in whole plant growth and development.…”