Page 147 - Algae Anatomy, Biochemistry, and Biotechnology

130 Algae: Anatomy, Biochemistry, and Biotechnology

FIGURE 2.88 Ejectile organelle of Bigelowiella natans before (left) and during discharge (right).

Chlorarachniophyta
Structures interpreted as ejectile organelles (extrusomes) are commonly seen in Bigelowiella
natans. Each organelle resides in a vesicle and consists of two parts. The anterior part is very
short, measuring ca. 0.15 mm in length, whereas the posterior part is ca. 0.55 mm long. The pos-
terior part has a very distinct substructure, comprising a core surrounded by a less opaque cylinder.
The cylinder is lined by a thin membrane-like structure, whereas the core comprises a thinner mem-
branous structure surrounded by a more opaque one. The structure of the anterior part of the ejectile
organelle is less well defined. Although it is clear that the membrane of the surrounding vesicle
forms an indentation ring that separates the two parts of the ejectile organelle, the path of the mem-
brane in this area is less clear. It appears that only the core of the organelle is discharged, the core
apparently turning inside out during discharge. The surrounding cylinder seems to remain in place.
The fate of the anterior part of the ejectile organelle after discharge has not been ascertained
(Figure 2.88).

Chlorophyta
Some Pyramimonas species (Prasinophyceae) contain ejectile structures similar to the ejectosomes
of Cryptophyta. In the undischarged state, they consist of a coiled ribbon, which upon discharge
forms a hollow tube tapered at both ends.

SUGGESTED READING
Albertano, P., Barsanti, L., Passarelli, V., and Gualtieri, P., A complex photoreceptive structure in the cyano-
bacterium Leptolyngbya sp., Micron, 31, 27, 2000.
Andersen, R. A., Biology and systematic of heterokont and haptophyte algae, American Journal of Botany, 91,
1508–1522, 2004.
Barlow, H. B., The physical limits of visual discrimination, in Photophysiology, Giese, A., Ed., Academic
Press, New York, 1964.
Barsanti, V., Passarelli, V., Walne, P.L., and Gualtieri, P. In vivo photocycle of the Euglena gracilis photo-
receptor, Biophysical Journal, 72, 545, 1997.