Chapter 13

Heterokontophyta

PINGUIOPHYCEAE

The Pinguiophyceae is a class of marine planktonic algae that were previously classed as “chrysophytes.” Analysis of nuclear-encoded 18S rRNA and chloroplast-encoded rbcL gene sequences uncovered the close relationship of the organisms in this class (Kawachi et al., 2002). The class is characterized by unusually high concentrations of polyunsaturated acids, especially 20:5 (n-3) (EPAeicosapentaenoic acid) in the cells (Kawachi et al., 1996) (Fig. 13.1). These fatty acids are the basis for choosing the latin noun “Pingue” (meaning fat,

Fig. 13.1 The structure of eicosapentaenoic acid, a

polyunsaturated fatty acid found in high concentrations in

algae in the Pinguiophyceae.

grease) as the root of the class name. The high percentage of unsaturated fatty acids, and the lack of a cell wall, make these algae desirable as a source of unsaturated fatty acids and of animal feed.

The cells (Figs. 13.2, 13.3) (Honda and Inouye,

Fig. 13.2 Ultrastructural

characteristics of an alga in the

Pinguiophyceae.

358 CHLOROPLAST E.R.: EVOLUTION OF TWO MEMBRANES

Fig. 13.3 Algae classified in the Pinguiophyceae.

2002) are derived from a typical heterokont ancestor with an anterior tinsel flagellum with tripartite hairs and a posterior smooth whiplash flagellum (although many of the genera have lost one or both flagella through evolution). The chloroplasts have two membranes of chloroplast endoplasmic reticulum, the outer membrane continuous with the nuclear envelope. A girdle band of thylakoids occurs under the chloroplast envelope. Pyrenoids occur in the chloroplast and the mitochondria have tubular cristae. Chlorophyll a and chlorophyll c-related pigments as well as fucoxanthin, violaxanthin, zeaxanthin, and - carotene are present.

REFERENCES

Honda, D., and Inouye, I. (2002). Ultrastructure and taxonomy of a marine photosynthetic stramenopile Phaeomonas parva gen. et sp. nov. (Pinguiophyceae) with emphasis on the flagellar apparatus architecture. Phycol. Res. 50:75–89.

Kawachi, M., Kato, M., Ikemoto, H., and Miiyachi, S. (1996). Fatty acid composition of a new marine picoplankton species of the Chromophyta. J. Appl. Phycol. 8:397–401.

Kawachi, M., Inouye, I., Honda, D., et al. (2002). The Pinguiophyceae classis nova, a new class of photosynthetic stramenopiles whose members produce large amounts of omega-3 fatty acids. Phycol. Res. 50:31–47.