Dunaliella

1. Dunaliella primolecta Butcher (ref. ID; 3730)

Dunaliella primolecta Butcher (ref. ID; 3730)

Descriptions

• Light microscopy: Flagellates in logarithmic phase are pear-shaped or ovoid and measure 10x7 um. The 2 equally long acronematic flagella have an anterior insertion directly beneath which, in living specimens, are 2 refractile rods probably representing the Golgi apparatus. Small refractile granules are present in the anterior half of living flagellates. The stigma has an anterior peripheral location in a voluminous chloroplast which obscures the nucleus. The cup-shaped chloroplast with its pyrenoid, the nucleus and nucleolus, and the cytoplasm containing clear vacuoles are readily seen in sectioned flagellates. Living organisms from stationary phase are rounded (10 um diameter) and also possess refractile granules. Sectioned flagellates have refractile starch granules in the chloroplast and lipid vacuoles in the cytoplasm but lack the clear vacuoles of flagellates from the logarithmic phase. (ref. ID; 3730)
• Electron microscopy: Flagellar axonemes have the conventional 9+2 pattern of microtubules, and the basal bodies consist of 9 peripheral triplets of microtubules. The basal bodies are connected by a 50 nm thick banded plate. Up to 2 additional basal bodies may be seen near the flagellar basal bodies and on occasion an intracellular flagellar axoneme has been observed lying between the plasmalemma and the chloroplast. The junction of the banded plate with each basal body gives rise to 2 rootlets. Each of the 4 rootlets comprises a fibrous component, which in sections has an amorphous substructure, and a microtubular component. At its origin each rootlet has 4 microtubules in a 3-over-1 pattern, the single microtubule lying between 2 fibrous elements. After a short distance the rootlets occupy subplasmalemmar positions, the fibrous component branches and the number of microtubules associated with the fibrous components decreases. The commonest pattern of rootlet construction is 2 microtubules associated with a single fibrous element ~150 nm thick. The rootlet's fibrous component is always seen in association with microtubules, although the subplasmalemmar microtubules are frequently seen, especially in the posterior half of the flagellate, without the fibrous component. Another rootlet arising from near the basal bodies has the form of a cross-striated fibril, ~100 nm thick. It consists of fine longitudinally arranged filaments traversed by bars every 80-90 nm. Close to the basal bodies is a reniform body, 300x130 nm, of amorphous substructure. The flagellar membrane is continuous with the 8 nm plasmalemma of the organism's body. There is no cell wall. In some preparations the plasmalemma's external surface has a layer of amorphous material of variable thickness and distribution. Separated from the plasmalemma by a thin layer of cytoplasm is the chloroplast. It contains interconnected groups of thylakoids in a finely granular matrix in which 100 nm diameter lipid inclusions are sparsely distributed. The plate-like stigma, 1 or 2 layers of closed packed 100-200 nm diameter lipid globules, lies free in the matrix. The matrix contains also starch granules which in logarithmic-phase flagellates are small and few, except for those enveloping the homogeneously granular pyrenoid. The pyrenoid is penetrated by pairs of thylakoids that have terminal distensions containing electron-dense inclusions. The chloroplast of stationary-phase organisms contains larger and more numerous starch granules. The nucleus contains roughly centrally placed nucleolus and scattered areas of heterochromatin (some adhering to the nuclear envelope's inner surface) embedded in a lightly granular euchromatin. The outer surface of the envelope has attached ribosomes and extensions in the form of rough endoplasmic reticulum (ER). Rough ER is also seen without any apparent connection to the nucleus. Mitochondrial profiles are either small and discrete or branched. The rounded plate-like cristae are "bristly" on the surfaces facing the mitochondrial matrix. The cytoplasm contains small numbers of microbody-like organelles with a 6 nm thick membrane which encloses a finely granular matrix lacking a crystalloid inclusion. In logarithmic-phase flagellates, numerous vacuoles with an 8 nm thick membrane and electron-lucent contents are present in the cytoplasm. In stationary-phase cells, these vacuoles are not so apparent and seem to be replaced by slightly smaller single-membraned vacuoles containing variable amounts of amorphous or membranous material. The Golgi apparatus lies between the basal bodies and the nucleus and consists of 2 or 3 dictyosomes of cisternae surrounded by numerous vesicles. An element of ER (the subtending ER) with ribosomes attached to its distal surface is separated from the forming cisternae by a cluster of 60-80 nm diameter smooth vesicles. Coated vesicles of the same size may also occupy this zone but apparently not at the same time as the smooth vesicles. Both kinds of vesicle, described here as pre-cisternal, seem to bud off from the subtending ER. Each dictyosome has 10-15 cisternae from whose peripheral surfaces post-cisternal vesicles appear to develop. These are of 4 morphologic types: (a) 60-80 nm diameter, smooth spherical vesicles; (b) smooth vesicles, 100-200 nm diameter; (c) coated vesicles, ~100 nm diameter; and (d) multivesicular bodies (mvbs), ~200 nm diameter. Mvbs are also seen outside the Golgi zone. Golgi-associated mvbs and coated vesicles are usually less numerous than smooth vesicles, although on occasion dictyosomes have been noted where coated vesicles almost entirely excluded smooth vesicles. Vesicles similar to the larger post-cisternal smooth vesicles occupy subplasmalemmar positions and appear to make contact with the surface membrane. Electron-dense Gomori reaction product is localized in Golgi cisternae, especially in their peripheral dilations, and in post-cisternal smooth and coated vesicles in both logarithmic- and stationary-phase flagellate. The reaction product is absent from these structures in flagellates treated with NaF-containing and substrate-free control incubation media. The product was not unequivocally demonstrated in pre-cisternal vesicles or mvbs, but deposits were present in some single-membraned clear vacuoles; however, similar deposits were present also in such vacuoles in organisms incubated in control incubation mixtures. In stationary-phase flagellates the membranous organelles are closely packed together; the starch-distended chloroplast and the cytoplasmic lipid, in the form of spherical vacuoles without a membrane (absent from logarithmic-phase organisms), leave only a sparse supporting ribosome-containing groundplasm. These cells also contain small numbers of autophagosome-like bodies, i.e. 1- or 2-membraned vacuoles enclosing mitochondria or volumes of cytoplasm containing ribosomes and ER. Gomori reaction product has not been localized in these structures. (ref. ID; 3730)