Paola Mariani,1 and
1Dipartimento di Biologia, Università di Padova, Via U. Bassi 58/B, 35131 Padova, Italy; 2Dipartimento di Biotecnologie Agrarie, Università di Padova, Viale dell'Università 16, 35020 Legnaro, Padova, Italy
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Accepted 8 July 2012.
Oligogalacturonides are pectic fragments of the plant cell wall, whose signaling role has been described thus far during plant development and plant-pathogen interactions. In the present work, we evaluated the potential involvement of oligogalacturonides in the molecular communications between legumes and rhizobia during the establishment of nitrogen-fixing symbiosis. Oligogalacturonides with a degree of polymerization of 10 to 15 were found to trigger a rapid intracellular production of reactive oxygen species in Rhizobium leguminosarum bv. viciae 3841. Accumulation of H2O2, detected by both 2′,7′-dichlorodihydrofluorescein diacetate–based fluorescence and electron-dense deposits of cerium perhydroxides, was transient and did not affect bacterial cell viability, due to the prompt activation of the katG gene encoding a catalase. Calcium measurements carried out in R. leguminosarum transformed with the bioluminescent Ca2+ reporter aequorin demonstrated the induction of a rapid and remarkable intracellular Ca2+ increase in response to oligogalacturonides. When applied jointly with naringenin, oligogalacturonides effectively inhibited flavonoid-induced nod gene expression, indicating an antagonistic interplay between oligogalacturonides and inducing flavonoids in the early stages of plant root colonization. The above data suggest a novel role for oligogalacturonides as signaling molecules released in the rhizosphere in the initial rhizobium–legume interaction.
© 2012 The American Phytopathological Society