Abstract
alpha-1,4-Linked oligogalacturonides (OGs) inhibit auxin-regulated transcriptional activation of a rolB-beta-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 H(2)O(2) 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 H(2)O(2) accumulation(.) However, OG concentration for half-maximal induction of H(2)O(2) accumulation is approximately 3-fold higher than that for half-maximal inhibition of rolB promoter activity. The inhibition of rolB promoter activity is not influenced by the addition of catalase or superoxide dismutase, suggesting that H(2)O(2) and superoxide are not involved in this effect. A fungal oligo-beta-glucan elicitor induces extracellular H(2)O(2) accumulation at comparable or higher levels than those observed with OGs, but does not prevent the auxin-induced accumulation of GUS. We conclude that H(2)O(2) produced upon treatment with OGs is not involved in the inhibition of the auxin-induced expression of the rolB gene.