Page 127 - Algae Anatomy, Biochemistry, and Biotechnology

110 Algae: Anatomy, Biochemistry, and Biotechnology

FIGURE 2.73 Absorption spectra of the photoreceptor ground state (continuous gray line) and excited state
(continuous black line) and absorption spectrum of eyespot (dotted line) of Euglena gracilis. The photocycle of
the photoreceptor and shading effect of the eyespot are shown in the bottom part of the figure.

photocurrent could be propagated through paraxial rod filaments via charge transfer between rod
proteins, which in turn generates longitudinal waves of contraction along the paraxial rod. The con-
tractility of the rod should regulate the flagellum movement, turning the cell body towards the light
source. The ground state of the photoreceptor is restored when the photoreceptor again achieves the
alignment with the light.
The dynamics of the light alignment of a model Euglena gracilis that obeys the earlier men-
tioned constraints is shown in Figure 2.74. The initial orientation of the cell is perpendicular to
the light direction, but in few seconds, E. gracilis is completely aligned with the light. The CRC
Handbook on Organic Photochemistry and Photobiology (2004) is an excellent text that covers
all the aspects of algae photobiology.