Extracellular H2O2 induced by oligogalacturonides is not involved in the inhibition of the auxin-regulated rolB gene expression in tobacco leaf explants

a-1,4-Linked oligogalacturonides (OGs) inhibit auxin-regulated transcriptional activation of a rolB-b-glucuronidase (GUS) gene fusion in tobacco (Nicotiana tabacum) leaf explants (D. Bellincampi, M. Cardarelli, D. Zaghi, G. Serino, G. Salvi, C. Gatz, F. Cervone, M.M. Altamura, P. Costantino, G. De Lorenzo [1996] Plant Cell 8: 477–487). In this paper we show that inhibition by OGs is very rapid, with a short lag time, and takes place even after rolB promoter activation has initiated. OGs also induce a transient and catalase-sensitive accumulation of H2O2 in the leaf explant culture medium. OGs with a degree of polymerization from 12 to 15 are required for both the inhibition of the auxin-induced rolB-driven accumulation of GUS and the induction of H2O2 accumulation. However, OG concentration for half-maximal induction of H2O2 accumulation is approximately 3-fold higher than that for halfmaximal inhibition of rolB promoter activity. The inhibition of rolB promoter activity is not influenced by the addition of catalase or superoxide dismutase, suggesting that H2O2 and superoxide are not involved in this effect. A fungal oligo-b-glucan elicitor induces extracellular H2O2 accumulation at comparable or higher levels than those observed with OGs, but does not prevent the auxininduced accumulation of GUS. We conclude that H2O2 produced upon treatment with OGs is not involved in the inhibition of the auxin-induced expression of the rolB gene.