Page 88 - Algae Anatomy, Biochemistry, and Biotechnology

Anatomy 71

FIGURE 2.44 Transmission electron microscopy image of the transition zone of Ochromonas danica in
transverse section (a) (Bar: 0.20 mm); longitudinal section of the short flagellum of Ochromonas (b);
arrows point to the double rows of punctae representing the turn of the helix. (Bar: 0.40 mm.)

13 protofilaments and the incomplete tubules B and C have 10 protofilaments. The proximal part of
the basal body contains a fibrogranular structure termed the cartwheel, composed of a longitudinal
central tubule and nine series of spokes joined to the triplets. This structure seems to be present in
nearly all species of algae, with variations reported mainly for the length of the basal body. While
most green algae usually possess very short basal bodies (250–450 nm), those of the Prasino-
phyceae are often twice as long (560–690 nm). Some members of the Haptophyta, such as Chry-
sochromulina, also possess very long basal bodies (850–875 nm), but this length can reach a value
of 1300 nm in some Euglenophyta such as Entosiphon.
In some Chlorophyta two structures are present in association with the proximal ends of the
basal bodies: the terminal cap and the proximal sheaths. The terminal cap is a more or less promi-
nent electron-dense flap located on the anterior surface of the basal body, which folds over and
covers in part its proximal end. The proximal sheath is located posterior to the proximal end of
the basal body, and can have a half-cylindrical shape or be wedge-shaped, narrow proximally,
and broad distally.

FIGURE 2.45 Type 5 transition zone (Chlorophyta).