Figure 3.

Cellular Dynamics Associated with AM Colonization of D. carota Root Tissues.

Identical fluorescent ER labeling and color coding as in Figure 1. Bars = 10 μm.

(A) A PPA (arrowheads) was assembled in an epidermal cell underneath the fungal hyphopodium (hp) contact point (white dot). The position of the nucleus (n) is indicated.

(B) Orthogonal section (x–z side view) perpendicular to the root axis through a fungal penetration site in the epidermis (white dot). The hypha produced by the hyphopodium (hp) penetrated into the epidermal (e) cell lumen, and the underlying outer cortical (oc) cell assembled a broad PPA (arrowheads) connected to the nucleus.

(C) and (D) Aligned PPAs in a file of inner cortical cells ahead of an intracellular hypha (h) growing from left to right. The area outlined in (C) is magnified in (D), where progressive stages in PPA development can be observed from right to left. These polarized PPAs were characterized by a large aggregation of ER (arrow) directed toward the incoming fungus, a central enlarged nucleus and a narrow ER bridge (arrowhead) directed toward the following cell in the file.

(E) Sixteen hours later, the inner cortical cells imaged in (D) were colonized by broad coiled hyphae. The nuclei maintained their central position, and the hyphae were surrounded by a thin layer of ER.

(F) An inner cortical cell colonized by a broad hypha with localized prebranching aggregations of ER (arrowheads). One of these aggregations was associated with a budding hyphal branch. The host cell nucleus was in a central position, partly hidden by the hypha.

(G) Mature intercalary arbuscules inside three adjacent inner cortical cells from a longitudinal root section. The large main hyphae (h) were surrounded by fine branches (br) covered by a dense network of ER.