Ref ID : 722
Harald Netzel; [Formation of the thecal wall by polyphase secretion in the testate amoeba Netzelia oviformis (Rhizopodea, Lobosia)]. Arch.Protistenk 127:351-381, 1983
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1. During the 60 to 90 min of its vegetative reproduction by binary fission it takes the thecamoeba Netzelia oviformis about 20 min to form the thecal wall. 2. The cytoplasmic anlage is covered by a thin layer of secretion that presumably prevents loss of building material to the surrounding medium. 3. Inorganic building blocks are siliceous idiosomes of various shapes and sizes, contained in vesicles. Being transported to the cortex of the anlage they are arranged in one layer-long axis parallel to the surface-and extruded almost simultaneously (first exocytosis). 4. The organic building material, two types of thecagenous granules with complex ultrastructure (sieve-plate granules, smaller droplet granules), are prefabricated in the Golgi apparatus. 5. The sieve-plate granules are transported within their Golgi-vesicles to the cortex of the anlage to form a single discontinuous stratum. At the base of cytoplasmic lamellae protruding into the space between the idiosomes the granules become orientated isopolarly (sieve-plate pointing towards the interior of the cell) and are extruded nearly simultaneously into the joints between the idiosomes (second exocytosis). The resulting mosaic pattern and network, respectively, can be explained by assuming that vesicular membrane fuses with plasmalemma, only. 6. The excentric lumen of the sieve-plate granules opens, the sieve-plate now facing the external medium; the lateral matrix of the granules loosens and adheres to the adjacent idiosomes which thus become attached to one another by the resulting cement ("granular cement" theory). 7. During this process of loosening and transformation the ground plate of the granules remains attached to the tip of cytoplasic villi. 8. Subsequently, the droplet granules are secreted predominantly into narrow joints between idiosomes and transformed into cement (third exocytosis); the bowl-shaped lumen of these granules is oriented towards the cell and enlarges to a roughly spherical lumen in the cement. (Marginal flocks and fringes, centripetally deposited within these spaces, presumably represent the ultrastructural substratum of the colouring of the theca, which intensifies with age.) 9. Hardening of the cement after the species-specific morphogenesis of the new theca is accompanied by a recondensation of the matrix. 10. Difflugia tuberculata is transferred to the genus Netzelia as N. tuberculata on the basis of far-reaching ultrastructural similarities. 11. Indications towards occurrence of granular cement or thecagenous granules, respectively, in other thecamoebae are compiled. The use of thecagenous granules appears to be a wide-spread phenomenon among the Lobosia.