The ultrastructure of Chlamydomonas pseudopertusa (Chlamydomonadaceae, Chlorophyta)

摘要

The structure of the unicellular volvocophycean alga Chlamydomonas pseudopertusa Ettl (strain 42.72 SAG) of the Amphichloris group was studied by light and transmission electron microscopies. As a rule, the cells are mostly ellipsoid-cylindrical or cylindrical in shape and in culture medium N 12 they are mostly swimmers, whereas in medium N 1 they remain inside the maternal cells for a long time. Two contractile vacuoles are located near the basal bodies of the two flagella which are equal to the cell length. The cell wall consists of two layers and bears a papilla formed by the outer part of the inner layer. The plasmalemma is usually invaginated and at the apical end it is involved in papilla formation. The chloroplast has thylakoids usually combined in two to three and stroma with numerous ribosomes, some osmiophilic globules and starch grains. The structure of pyrenoid also is more clearly defined in medium N 12. It is surrounded by a sheath of 8-12 starch grains and has an electron-dense stroma, traversed by paired thylakoids. The stigma is formed by two rows of pigment globules. The nucleus is of the simple chromocentric type. It forms characteristic long lobes in large cells. The fine structure of C.pseudopertusa is similar to that of C.desmidii, especially in the cell wall composition, pyrenoid sheath, thylakoid arrangement and nuclear form changes.