Page 104 - Algae Anatomy, Biochemistry, and Biotechnology

Anatomy 87

Examples of main swimming patterns among algae will be described as follows.
In Ochromonas sp. (Heterokontophyta) only the flagellum bearing hairs seems to be active
during swimming. It is directed forward and executes simultaneous undulatory and helical
waves that travel from its base to the tip. The resulting flagellum movements cause the whole
body of the cell to rotate as it moves forwards. The shorter flagellum trails backward passively,
lying against the cell; it is capable of acting as a rudder to steer the cells. The two rows of stiff
hairs cause a reversal of the flagellum thrust. Water is propelled along the flagellum from the tip
to the base, so that the cell is towed forward in the direction of the flagellum (Figure 2.59).
In desmokont dinoflagellates such as Prorocentrum sp., the longitudinal flagellum, which extends
apically, beats with an anterior-to-posterior whipping action, generating a wave in a tip-to-base mode.
The second flagellum, perpendicular to the first, is coiled and attached to the cell body except for the
tip, which beats in a whiplash motion, while the attached part undulates (Figure 2.60). In dinokont
dinoflagellates, such as Peridinium sp. or Gymnodinium sp., the two flagella emerge at the intersection
of the cingulum (transverse furrow) and sulcus (longitudinal sulcus). The longitudinal flagellum
extends apically running in the sulcus and is the propelling and steering flagellum, while the
ribbon-shaped transverse flagellum is coiled, lies perpendicular to the first and runs around the cell
in the cingulum. It is thought to be responsible for driving the cell forward and it also brings about
rotation. The longitudinal flagellum beats with a planar waveform, which contributes to forward
movement. The longitudinal flagellum can also reverse the swimming direction: it stops beating,
points in a different direction by bending, and then resumes beating. This steering ability is related
to change in orientation of basal bodies and contraction of the structures associated to the
axoneme. In the transverse flagellum, a spiral wave generated in a base-to-tip mode is propagated
along the axoneme, bringing about backward thrust and rotation at the same time (Figure 2.61).
As described earlier, the emergent flagellum of Euglena sp. (Euglenophyta), bears simple hairs
3–4 mm long. These long hairs are arranged in tufts of three to four and form a single row that runs
along the flagellum spirally with a low pitch. The flagellar hairs increase the thrust of the flagellum
against the surrounding water. During swimming the long flagellum trails beside the cell body and
performs helical waves, generated in a base-to-tip mode (Figure 2.62).
A peculiar swimming pattern is present in the ovoid zoospores of Chlorarachnion reptans and
Bigelowiella natans (Chlorarachniophyta), which bear a single flagellum inserted a little below the
cell apex. This flagellum bears very delicate hairs markedly different from the tubular hairs of
Heterokontophyta. During swimming the flagellum wraps back around the cell in a downward
spiral, lying in a groove along the cell body. The cells rotate around the longitudinal axis during
swimming and the anterior or posterior end of the cell moves in either narrow or wide helical
path which appears as a side-to-side roking or wobbling (Figure 2.63).

FIGURE 2.59 Swimming pattern of Ochromonas danica.