Page 93 - Algae Anatomy, Biochemistry, and Biotechnology

76 Algae: Anatomy, Biochemistry, and Biotechnology

The ultrastructure of the flagellar root system has been described only in one species of Bacillar-
iophyceae, Biddulphia laevis. In the spindle-shaped spermatoids of this centric diatom a system of
microtubules radiates from the only basal body present into the cell, to form a cone on the anterior
part of the nucleus, and at least some of these microtubules extend throughout the length of the
cell. They appear to maintain the elongated shape of the nucleus, and thus probably of the cell.
An elaborate root system connects the basal bodies to the anterior surface of the nucleus in the
Raphidophyceae. In Chattonella two or three roots have been described, one multi-layered associ-
ated with the pleuronematic flagellum, and one with the smooth flagellum. The latter is a band of
9–10 microtubules which extends from the anterior part of the cell, passing between the basal
bodies, and joining with other microtubules before extending along the nucleus in a depression
of its surface. A large number of distinctly cross-banded fibrous roots are also present, extending
from the flagellar bases to ensheathe the anterior cone of the nucleus.
In the Phaeophyceae the structure of the flagellar root system appears remarkably uniform. The
main characteristic of the system is the root supporting the flat, elastic proboscis in spermatozoids
of brown algae. In Fucus this root is very broad, contains usually 7 microtubules (but there can be
up to 15 microtubules), which travel from the base of the anterior flagellum along the plasmalemma
to the anterior end of the cell, where the proboscis is located. Here, they bend back and run along the
cell membrane on the opposite side. A bypassing microtubular root, of about five microtubules,
originates in the anterior part of the cell, runs along the proboscis root, bypasses the basal
bodies, without contact, and continues towards the posterior part of the cell. Other two minor micro-
tubular roots, consisting of only one microtubule, are present, one extending anteriorly, the other
posteriorly. The basal bodies are interlinked by three cross-banded connectives, the deltoid, the
strap-shaped, and the button-shaped bands (Figure 2.50).

Haptophyta
In the Haptophyta there are different types of flagellar roots. Members of the order Pavlovales, such
as Pavlova and Diacronema, possess a fibrous root, non-striated, which extends from the base of the
anterior flagellum, and passes into the cell along the inner face of the nucleus, becoming progress-
ively wider. In some species, another fibrous root originates at the base of the haptonema. Two
microtubular roots extend from the base of the posterior flagellum: a seven-stranded root which
runs under the periplast, and a two-stranded root arising almost at right angles to the seven-stranded
root, running inside the cell opposite to the haptonema. Fibrous connecting bands are present
between the basal bodies (Figure 2.51). In the algae of the order Isochrysidales, such as Pleurochry-
sis, the structure of the flagellar root system is more complex. Three main microtubular roots are
associated with the two basal bodies, two broad roots, no. 1 and no. 2, arising near the left flagellum,
and a smaller root, no. 3, arising near the right flagellum. Root no. 1 extends from the basal body up
towards the cell apex and then curves backwards to run inside the cell. A fibrous root is associated
with root no. 1. Closely packed microtubules organized in a bundle branch off perpendicularly from
both root no. 1 and root no. 2. The basal bodies are connected to each other by distal, intermediate,
and proximal connecting bands. Accessory connecting bands link the haptonema to the basal bodies
and the left basal body to the broad microtubular root no. 1 (Figure 2.52).

Cryptophyta
The flagellar roots of these algae include two characteristic components, the rhizostyle and the com-
pound rootlet. The rhizostyle is a posteriorly directed microtubular structure. It originates alongside
the basal body of the dorsal flagellum, extends deep into the cell, parallel to the gullet, behind the
layer of trichocysts, and ends in the posterior part of the cell. On the way, it runs through a groove in
the nuclear surface. In many cryptomonads, such as Chilomonas, each of the rhizostyle microtubule
bears a wing-like lamellar projection. The compound rootlet consists of a cross-banded fibrous band
and microtubular roots. The fibrous band originates from the basal bodies of the dorsal flagellum,