Fig. 1

Increase in cell divisions and nuclear areas throughout AM colonization compared to uncolonized roots. The figure presents a collection of representative z-stack projections of uncolonized and mycorrhized wild-type M. truncatula ROCs. Panel (a) shows small sized nuclei in epidermal (epid), cortical (cort) and stele cells of an uncolonized root section. A colonized root section is shown in (b), where an Intraradical hypha (hy) of G. margarita (white dashed lines) penetrating from epidermal to cortical cells is visible, alongside several arbusculated cortical cells (ar). The latter display enlarged nuclei (white arrows), surrounded by small fungal nuclei (asterisks). Panels (c) and (d) show the appearance of ectopic cell divisions in the root cortex during progressive steps of AM colonization: couples of split cells (yellow dashed lines) are localized in proximity of arbuscules (c) and intraradical hyphae growing between cortical cells (d). The large nuclear size (arrows) in arbusculated and neighbouring cells (nc) is evident when compared to non-colonized cortical cells from the same root (panel e), as well as cortical cells from an uninoculated root (panel f). Scale bars = 50 μm