Hydrogen peroxide accumulation in Medicago truncatula roots colonized by the arbuscular mycorrhiza-forming fungus Glomus intraradices

Abstract.

The diaminobenzidine (DAB) staining technique was used to examine the accumulation of H₂O₂ in parts of roots of Medicago truncatula Gaertn. colonized by the arbuscular mycorrhiza (AM)-forming fungus Glomus intraradices Schenk and Smith. At the cellular level, the combination of bright-field and fluorescence microscopy revealed that a brownish stain, indicative of H₂O₂ accumulation was present within cortical root cells in the space occupied by arbuscules. Accumulation of H₂O₂ was especially pronounced in cells containing arbuscules that were clumped and less branched. Moreover, H₂O₂ accumulated around hyphal tips attempting to penetrate a host cell. In contrast, no H₂O₂ accumulation was observed in hyphal tips growing along the middle lamella, or in appressoria or vesicles. On the basis of these findings we suggest that a locally restricted oxidative burst is involved in the temporal and spatial control of the intracellular colonization of M. truncatula cells by the AM-forming fungus G. intraradices.