The cytology of the testaceous rhizopod Lesquereusia spiralis (Ehrenberg) Penard. I. Ultrastructure and shell formation

Abstract

Ultrastructure and shell formation in the testaceous ameba, Lesquereusia spiralis, were investigated with both scanning and transmission electron microscopy and X-ray microanalysis. The nucleus, surrounded by a fibrous lamina, contains multiple nucleoli. The cytoplasm, containing a well developed granular endoplasmic reticulum, also contains remnants of starch granules in stages of digestion. Spherical aggregates of ribosome-like particles may be seen. Golgi complexes seem to produce both a nonordered fibrous material and an electron dense vesicle.Only the latter appears to bleb off from the Golgi complex. X-ray microanalysis demonstration of silicon in Golgi vesicles and in some dense vesicles suggests that the fibrous component of the cisternae may take up and concentrate silica to form the electron-dense component of the vesicles. Membrane-bound siliceous crystals are often seen adjacent to the Golgi, suggesting either a Golgi origin or platelet formation in vesicles after release from the Golgi complex. Both electron-dense bodies and siliceous platelets are released from the cell by a process similar to apocrine secretion and may be seen outside the cell in route to the shell during shell morphogenesis. Shell development involves fusion of electron-dense bodies to form a matrix, positioning of siliceous platelets in this matrix parallel to the shell surface, and development of a system of matrix chambers. A particulate glycoconjugate is released to the shell surface upon rupture of the matrix chamber.Although the basic morphology of the testaceous ameba has been known for quite some time (see Penard, '02; Hall, '53; Kudo, '66 for general reviews), modern cytological methodology has been used only rarely (Stump, '59, '71; Moraczewski, '691 in studies of this group. The ameba Lesquereusia spiralis is of some cytological interest in that it possesses a shell composed of siliceous platelets positioned in an organic matrix. Previous light microscopical studies (Stump, '59, '71; Harrison et al., '75) reported the presence of shell platelets in the cytoplasm of L. spiralis, suggesting that the platelets were a secretory product.Silica deposition as opal is recognized in a variety of tissues of many plants (Lewin and Reiman, '69; Kaufmann et al., '73). In at least some cases (Sangster, '70, '71) opaline phytolith formation is a passive process involving nonmetabolic mechanisms. In freshwater sponges, silica is deposited through secretory activities of the membraneous silicalemma upon an intracellular organic skeleton to form spicules with species-specific characteristics (Drum, '68; Simpson and Vaccaro, '74). Although the development of the organic filamentous skeleton in the silicoblast is obviously under genetic control and involves cytochemically demonstrable synthetic activities (Harrison, '741, the exact process of spicule formation in the spongillids is not ). The present investigation employs scanning and transmission electron microscopy and X-ray microanalysis to describe both the morphology of L. s...

An Atlas of Sphagnum-Dwelling Testate Amoebae in Bulgaria

“…Most of the species with agglutinate shells, composed of quartz grains (xenosomes), have poorly studied cell morphology because their shells are opaque and robust, with thick walls, which prevent the study of the cytoplasm by light and transmission electron microscopy. us, much of our knowledge on the cell structure of testate amoebae is mainly due to the studies of species with proteinaceous, siliceous or calcareous shells (Charret 1964, Hedley and Ogden 1973, 1974, 1977, Netzel 1975, Harrison et al 1976, Bonnet et al 1981, Golemansky et al 1987, Ogden and Coûteaux 1987, Anderson 1990, Ogden 1991.…”

Some Enzyme Activities in the Testate Amoeba Netzelia tuberculata1

“…The respiration and growth rates of some species have been determined in laboratory studies (7, 11). Previous fine structural data for a variety of species ( 3 , 9, 10, 13) and cytochemical data for Lesquereusia (8) indicate that they possess mitochondria and exhibit cytoplasmic organization as found in many eukaryotic cells. For example, Netzelia tuberculata (Ogden, 1979) has a typical eukaryotic nucleus surrounded by mitochondria with tubular cristae and digestive vacuoles of varying size and degree of food digestion ( 3 ) .…”

Extra-, Inter-, and Intracellular Mineralization in Invertebrates and Algae

“…Examples are calcite spicules in the scleroblasts of the octocorals Leptogorgia (Kingsley & W atabe, 1982b) and Renilla (Dunkelberger & Watabe, 1974); calcareous spicules in epidermal spicule-forming cells of the acochilidacean molluscs (Rieger & Sterrer, 1975b); larval spines (see Okazaki et al, 1980), ossicles (Stricker, 1985), teeth (Kniprath, 1974), regenerated spines and tests (Shimizu & Yamada, 1980) in sclerocytes of echinoderms; aragonite spicules in scleroblasts of the didemnids (compound ascidians) (Kniprath & Lafargue, 1980); calcium phosphate stylets in styletocytes of nemertean worms (Stricker, 1984), and calcite coccoliths of unicellular algae (Wilbur & Watabe, 1963; see also Blackwelder et al, 1979). Silica structures are formed within vesicles of rhizopod amebae (Harrison et al, 1976), siliceous sponges (see Garrone et al, 1981), diatoms (see Volcani, 1981), radiolarians (Riedel & Sanfilippo., 1981), chrysophytes (McGrory & Leadbeater, 1981) and choanoflagellatcs (Leadbeater, 1981).…”