FIGURE 4.

An ultrastructural study of the extruded PT of Anncaliia algerae. (A) Light and transmission electron microscopy (TEM) showed the cross section of an extruded PT from spores. The lumen of the tube is filled with about eight alternating concentric thin ED and electron lucent (EL) rings of material. The outer wall of the PT is enclosed by a relatively thick ED wall which is in turn covered by additional rings of material. The outermost PT surface is a ring of medium dense fibrous material with tufts of fibers projecting outward (arrows). Bar is 100 nm. (B) CTEM of the distal end of PTs showed that end of the PT containing multiple tightly packed membranes (short arrows) that will give rise to the sporoplasm membrane “terminal sac.” Note the closed tip of the tube. Bar is 50 nm. (C) Tomogram of a portion of PT containing cargo and membranes, and its surface is covered with tufts of fibrillar material. The different PT structures are color coded to the various densities visible in the stacks of images and identified by color. (D) The tomogram was segmented and 3D models generated from it using Amira software. Reprinted with the permission of the publisher (Takvorian et al., 2019).