Spicule formation in the gorgonian coral Pseudoplexaura flagellosa. 1: Demonstration of intracellular and extracellular growth and the effect of ruthenium red during decalcification
Abstract:Spicule formation in the gorgonian Pseudoplexaura flagellosa (Houttuyn) is a complex event involving a transient intracellular step followed by a longer process of extracellular growth. The intracellular phase produces electron lucent vesicles 1–2 μm in diameter that are closely associated with mitochondria and the Golgi apparatus. The vesicles calcify and enlarge, forming one or more intracellular masses of polymorphic crystals that are released to the extracellular space or mesoglea. These calcified structures, the spicule primordia, serve as the focal points for continued growth through the agency of secondary sclerocytes in the mesoglea. Secondary sclerocytes do not form crystals within vesicles. Instead, several of these cells form a complex network of interdigitating, overlapping pseudopodia surrounding the primordia. Crystal formation appears to occur within the space between membrane and spicule although details of the process are not clear. The result of secondary growth is the integration of several primordia into a single immature spicule by formation of overlapping, concentric sheets of blade-like calcite crystals. As secondary growth continues, additional secondary sclerocytes settle on the spicular surface creating complex tubercles. The last step of spicule formation is characterized by a perispicular envelope created by the pseudopodia of separate but closely apposed secondary sclerocyte daughter cells. This stage produces the final layers of secondary growth over the entire spicule surface, sealing in the tubercular structures. Mature spicules are free of cellular material.
Additional experiments demonstrate that ruthenium red has a stabilizing influence on the spicule matrix, preventing its complete extraction during decalcification. Ruthenium red exerts its primary influence extracellularly and does not ordinarily prevent loss of matrix from the intracellular phase of primordium formation. These data support the morphological evidence that spicule formation in P. flagellosa is initially intracellular but is primarily an extracellular, multicellular event.
Document Type: Research Article
Publication date: 1987-03-01
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