HETEROKONTOPHYTA, SYNUROPHYCEAE	353

and either oscillates in place or swims sluggishly for at least 4 to 8 hours. During this time, the four chloroplasts assume a symmetrical orientation around the flagellar bases as is typical of vegetative Synura cells, and the two large chrysolaminarin vesicles fuse to occupy the cell posterior. The flagella are lost, and the zygote becomes spherical as cyst wall deposition begins. After 6 to 8 hours, a morphologically mature zygote statospore is produced. Mature zygospores are observed as solitary objects if the female gametes are solitary. If the female gametes are in a colony, then the zygospores take the place of the female gametes in the female colonies. Female colonies can have as many as eight statospores, apparently as the result of numerous cells serving as female gametes. The cyst is an unornamented sphere, 13 to 16 m in diameter, and has a single, small recessed pore that lacks a surrounding collar. Presumably, statospores germinate meiotically to produce haploid cells. The number of statospores produced is in the range of 1% to 20% of the vegetative cell density. In addition, some statospores are produced asexually and can be seen in the clones before they are mixed.

REFERENCES

Andersen, R. A. (1985). The flagellar apparatus of the golden alga Synura uvella: Four absolute orientations.

Protoplasma 128:94–106.

Andersen, R. A. (1987). Synurophyceae classis nov., a new class of algae. Am. J. Bot. 74:337–53.

Andersen, R. A., and Mulkey, T. J. (1983). The occurrence of chlorophylls c1 and c2 in the Chrysophyceae. J. Phycol. 19:289–94.

Andersen, R. A., van de Peer, Y., Potter, D., Sexton, J. P., Kawachi, M., and LaJeunesse, T. (1999). Phylogenetic analysis of the SSU rRNA from members of the Chrysophyceae. Protist 150:71–84.

Beech, P. L., Wetherbee, R., and Pickett-Heaps, J. D. (1990). Secretion and development of bristles in

Mallomonas splendens (Synurophyceae). J. Phycol. 26:112–22.

Dixit, S. S., Dixit, A. S., and Smol, J. P. (1999). Lake sediment chrysophyte scales from the northeastern

U.S.A. and their relationship to environmental variables. J. Phycol . 35:903–18.

Dürrschmidt, M. (1984). Studies on scale-bearing Chrysophyceae from the Giessen area, Federal Republic of Germany. Nord. J. Bot. 4:123–43.

Fott, B. (1962). Taxonomy of Mallomonas based on electron micrographs of scales. Preslia 34:69–84.

Klaveness, D., and Guillard, R. R. L. (1975). The requirement for silicon in Synura petersenii (Chrysophyceae). J. Phycol. 11:349–55.

Lavau, S., and Wetherbee, R. (1994). Structure and development of the scale case of Mallomonas adamas (Synurophyceae). Protoplasma 181:259–68.

Lavau, S., Saunders, G. W., and Wetherbee, R. (1997). A phylogenetic analysis of the Synurophyceae using molecular data and scale case morphology. J. Phycol. 33:135–51.

Leadbeater, B. S. C. (1990). Ultrastructure and assembly of the scale case in Synura (Synurophyceae Andersen). Br. Phycol. J. 25:117–32.

Ludwig, M., Lind, J. L., Miller, E. A., and Wetherbee, R. (1996). High molecular mass glycoprotein associated with the siliceous cell scales and bristles of Mallomonas splendens (Synurophyceae) may be involved in cell surface development and maintenance. Planta 199:219–28.

Pipes, L. D., and Leedale, G. F. (1992). Scale formation in

Tessellaria volvocina (Synurophyceae). Br. Phycol. J.

27:11–19.

Sandgren, C. D., and Flanagin, J. (1986). Heterothallic sexuality and density dependent encystment in the chrysophycean alga Synura petersenii Korsch. J. Phycol.

22:206–16.

Saxby-Rouen, K. J., Leadbeater, B. S. C., and Reynolds, C. S. (1997). The growth response of Synura petersenii (Synurophyceae) to photon flux density, temperature, and pH. Phycologia 36:233–43.

Schultz, T. F., Egerton-Warburton, L., Crawford, S. A., and Wetherbee, R. (2001). Identification of a 41kDa protein embedded in the biosilica of scales and bristles isolated from Mallomonas splendens

(Synurophyceae, Ochrophyta). Protist 152:315–27. Smol, J. P., Charles, D. F., and Whitehead, D. R. (1984).

Mallomonadacean microfossils provide evidence of recent lake acidification. Nature 307:628–30.

Tyler, P. A., Pipes, L. D., Croome, R. L., and Leedale, G. F. (1989). Tessellaria volvocina rediscovered. Br. Phycol. J.

24:329–37.

Chapter 12

Heterokontophyta

EUSTIGMATOPHYCEAE

Eustimatophytes are yellow-green unicells that occur in freshwater, brackish water, and seawater as well as in the soil. The cells are similar to those in the Xanthophyceae, but differ in having an eyespot outside the chloroplast (Fig. 12.1) (the eyespot in the Xanthophyceae is in the chloroplast)

(Hibberd and Leedale, 1970). Other characteristics of the class include a basal swelling of the tinsel flagellum adjacent to the eyespot, only chlorophyll a, chloroplasts without girdle lamellae and no peripheral ring of DNA, and chloroplast endoplasmic reticulum not connected to the nuclear envelope (Schnepf et al., 1996).

The eyespot (Figs. 12.1, 12.2) is a large orangered body at the anterior of the motile cell and

Fig. 12.1 (a) Diagrammatic representation of the basic morphology of a zoospore of the Eustigmatophyceae. (C) Chloroplast; (CER) chloroplast endoplasmic reticulum; (E) eyespot; (F) long flagellum; (FB) basal body of short flagellum; (FS) flagellar swelling;

(LV) lamellate vesicles; (N) nucleus. (b) Polyhedriella helvetica, zoospore and vegetative cells. (c) Chlorobotrys regularis. (d) Pleurochloris magna, vegetative cell and zoospore.

((a) after Hibberd and Leedale, 1972; (b) after Fritsch and John, 1942; (c) after Smith, 1950; (d) after Boye Petersen, 1932.)

HETEROKONTOPHYTA, EUSTIGMATOPHYCEAE	355

is completely independent of the chloroplast. It consists of an irregular group of droplets with no membrane around the whole complex of droplets. The flagellar sheath is extended to form a T- shaped flagellar swelling at the base of the tinsel flagellum (Figs. 12.1, 12.2). This swelling is always closely appressed to the plasmalemma in the region of the eyespot. In turn, in the eyespot there is a large droplet closely applied to the plasmalemma in the area of the flagellar swelling.

The chloroplasts of the Eustigmatophyceae have chlorophyll a and -carotene, with the two major xanthophylls being violaxanthin and vaucheriaxanthin (Whittle and Casselton, 1969; Antia and Cheng, 1982), the only difference in pigments compared to the Xanthophyceae being the presence of violaxanthin and the absence

of antheraxanthin. Violaxanthin is the major light-harvesting pigment in the Eustigmatophyceae (Owens et al., 1987).

The Eustigmatophyceae is a monophyletic group (Andersen et al., 1998). Most of the species produce zoospores with only a single emergent flagellum (Pleurochloris magna, Fig. 12.1(d);

Polyedriella helvetica, Fig. 12.1(b), Hibberd and Leedale, 1972), but there is a second basal body present, indicating that the cells had a biflagellate ancestor. The emergent flagellum is tinsel with microtubular hairs, and the flagellum is inserted subapically. Two of the algae in the class, Ellipsoidion acuminatum and Pseudocharaciopsis texensis (Fig. 12.2) (Lee and Bold, 1973), have zoospores with a long forward tinsel flagellum and a short posteriorly directed smooth

Fig. 12.2 Pseudocharaciopsis texensis: (a), (b) zoospores;

(c) vegetative cells. (CE) Chloroplast envelope; (CER) chloroplast endoplasmic reticulum; (E) eyespot; (F1) long flagellum; (F2) short flagellum; (G) Golgi; (LV) lamellate vacuoles; (Mt) microtubules;

(N) nucleus; (O) oil body. (After Lee and Bold, 1973.)

356 CHLOROPLAST E.R.: EVOLUTION OF TWO MEMBRANES

flagellum. One of the organisms, Chlorobotrys regularis (Fig. 12.1(c)), does not form zoospores (Hibberd, 1974).

REFERENCES

Andersen, R. A., Brett, R. W., Potter, D., and Sexton, J. P. (1998). Phylogeny of the Eustigmatophyceae based upon 18S rDNA, with emphasis on Nannochloropsis. Protist 149:61–74.

Antia, N. J., and Cheng, J. Y. (1982). The ketocarotenoids of two marine coccoid members of the Eustigmatophyceae. Br. Phycol. J. 17:39–50.

Boye Petersen, J. (1932). Einge neue Erdalgen. Arch. Protistenk. 76:395–408.

Fritsch, F. E., and John, R. P. (1942). An ecological and taxonomic study of the algae of British soils. II. Consideration of the species observed. I. Chlorophyceae. Ann. Bot. N.S. 6:371–95.

Hibberd, D. J. (1974). Observations on the cytology and ultrastructure of Chlorobotrys regularis (West) Bohlin with special reference to its taxonomic position in the Eustigmatophyceae. Br. Phycol. J. 9:37–46.

Hibberd, D. J., and Leedale, G. F. (1970). Eustigmatophyceae – a new algal class with unique organization of the motile cell. Nature 225:758–60.

Hibberd, D. J., and Leedale, G. F. (1972). Observations on the cytology and ultrastructure of the new algal class Eustigmatophyceae. Ann. Bot. N.S. 36:49–71.

Lee, K. W., and Bold, H. C. (1973). Pseudocharaciopsis texensis gen. et sp. nov., a new member of the Eustigmatophyceae. Br. Phycol. J. 8:31–7.

Owens, T. G., Gallagher, J. C., and Alberte, R. S. (1987). Photosynthetic light-harvesting function of violaxanthin in Nannochloropsis spp. (Eustigmatophyceae).

J. Phycol. 23:79–85.

Schnepf, E., Niemann, A., and Wilhelm, C. (1996).

Pseudostaurastrum limneticum, a Eustigmatophycean alga with astigmatic zoospores: morphogenesis, fine structure, pigment composition and taxonomy. Arch. Protistenk. 146:237–49.

Smith, G. M. (1950). The Freshwater Algae of the United States, 2nd edn. New York and London: McGraw-Hill.

Whittle, S. J., and Casselton, P. J. (1969). The chloroplast pigments of some green and yellow-green algae. Br. Phycol. J. 4:55–64.