Ultrastructure of the green flagellate Dunaliella tertiolecta (Chlorophyceae, Volvocales) with comparative notes on three other species

Abstract

The ultrastructure of Dunaliella tertiolecta, a naked, halotolerant unicellular green alga, is described and compared with ultrastructural features reported previously for three other species: D. bioculata, D. primolecta and D. salina. Most internal cell features are chlamy domonad in structure and arrangement. Conspicuous changes occur in D. tertiolecta between logarithmic and stationary growth phases. Vacuoles are more abundant and vac uolar inclusions have a different appearance in stationary as opposed to logarithmic phase cells. Thylakoids of the chloroplast are densely stacked in eight to ten layers in stationary phase cells, but are in stacks of two to four in logarithmic phase. Cytoplasmic and chloroplastic lipids, including eyespot granules, appear to increase with age of the cell. During logarith mic phase the endoplasmic reticulum shows greater proliferation. In cells subjected to increasing osmotic stress, large masses of dense-staining, tubular material is seen protrud ing and sometimes separating from the plasmalemma. Thylakoid stacking is more pro nounced in cells introduced into high salt concentration than in normal cells.

Exposure of Dunaliella tertiolecta to Lead and Aluminum: Toxicity and Effects on Ultrastructure

“…Two types of starch grains are clearly distinguished in the chloroplast, firstly those situated between thylakoids (stromal starch grains) and secondly those connected with the pyrenoid. In short, the appearance of the control cells matches the ultrastructural description of this organism given by Hoshaw and Maluf [20]. Cell ultrastructure was visibly affected by exposure to 0.5 mg L −1 Pb (see Fig.…”

The taxonomy of the genus Dunaliella (Chlorophyta, Dunaliellales) with emphasis on the marine and halophilic species

“…1, 2), especially in young cells. The ultrastructure of the flagellar apparatus of Dunaliella has been studied extensively (Peterfi and Manton 1968;Hyams and Chasey 1974;Eyden 1975;Hoshaw and Malouf 1981;Melkonian and Preisig 1984;Marano et al 1985;Watanabe and Floyd 1989;Marano 1992) and is typical of the Chlorophyceae and Prasinophyceae.…”

“…2,3). The degree of thylakoid stacking varies somewhat with light intensity and salinity (Pfeifhofer and Belton 1975;Vladimirova 1978;Hoshaw and Malouf 1981). The pyrenoid is usually surrounded by an amylosphere made up of starch grains and smaller starch grains may also be found free in the chloroplast stroma, especially in older cultures (Figs.…”

Ultrastructural changes in Dunaliella minuta following acute and chronic exposure to copper and cadmium

“…D. minuta, however, is a non-carotenogenic species (Borowitzka and Borowitzka 1988). Lipid increases occur in Dunaliella cells during stationary growth (Hoshaw and Maluf 1981). In the present study, cells were kept in logarithmic growth.…”