Silicon and Siliceous Structures in Biological Systems

The publication of this book was undertaken with two purposes in view: to bring together informatian on the deposition by living organ­ isms of unique skeletal structures composed of amorphous silica, and to review recent data on the involvement of silicon in physiological and biochemical processes. Although widely varying viewpoints are represented, all the contributors are very interested in the events in­ volved in the formatian of siliceaus structures and their function. Data presented deal with these questions in a variety of plant and animal systems, and at levels ranging from the evolutionary to the biochemical and ultrastructural. Innovations in electron microscopy and, indeed, the advent of electron microscopy itself, have stimulated many ultra­ structural studies of silica deposition, work which has deepened and widened the interest in those organisms which routinely produce "glassy skeletons. " The question of how silicon participates in biological systems in­ volves a spectrum of fields that indudes the chemistry of silicon per se, its biogeochemistry, biochemistry, ecology, and so forth. In this book, however, attention is focused up on the biological aspects of silicon and siliceous structures, with emphasis on the evolutian, phylogeny, morphology, and distribution of siliceaus structures, on the cellular as­ peets of silica deposition, and on the physiological and biochemical roles of silicon. This volume represents the first compilatian of such data. Because such a variety of subjects and fields are covered, the reader will have to glean for himself some of the comparative aspects of the data.

Terminology.- Techniques Applied to Biological Studies of Silicon.- Brief Survey of Chapters.- Morphogenesis of Silica in Biological Systems.- Evolutionary Aspects—Silicon and Calcium.- Section I. Physiological Aspects of Silicon.- 2. Silicon in the Cellular Metabolism of Diatoms.- Procedures.- Transport.- Silicon-induced Metabolic Processes.- References.- 3. Germanium-Silicon Interactions in Biological Systems.- Distribution in Biological Systems.- Germanium-Silicon Interactions.- Use of 68Ge as a Probe for Si.- Discussion.- References.- 4. Silicon in Bone Formation.- Bone Calcification.- Essentiality of Silicon.- Bone Formation.- Perspective.- References.- Section II. Siliceous Structures: Distribution, Deposition, Ultrastructure, Morphogenesis.- Algal Groups.- 5. Morphology and Phyletic Relationships of the Silicified Algae and the Archetypal Diatom—Monophyly or Polyphyly.- Silicified Groups Surveyed.- Cysts.- Phylogeny.- Origin of the Phyla.- Polyphyly, Monophyly, and Archetypal Diatoms.- References.- 6. The Siliceous Components of the Diatom Cell Wall and Their Morphological Variation.- The Frustule.- Cell Division and Valve Formation.- Size Reduction.- The Classical Taxonomy.- Summary.- References.- 7. Cell Wall Formation in Diatoms: Morphogenesis and Biochemistry.- Structure of the Cell Wall.- Morphogenesis.- Biochemistry.- References.- 8. Ultrastructure and Deposition of Silica in the Chrysophyceae.- Occurrence of Siliceous Structures on Chrysophycean Cells.- Procedures.- Terminology.- Chemistry of Siliceous Structures.- Ultrastructure and Deposition.- Discussion.- References.- Protozoa.- 9. Distribution and Forms of Siliceous Structures Among Protozoa.- Ecology.- Distribution of Structures.- Morphology of Structures.- Formation and Arrangement of Structures.- References.- 10. Ultrastructure and Deposition of Silica in Rhizopod Amebae.- Procedures.- Cytology.- Test Formation.- Golgi Complex and Silicon.- References.- 11. Ultrastructure and Deposition of Silica in Loricate Choanoflagellates.- Historical Note and Terminology.- Taxonomy.- Ecology.- Procedures.- Chemistry of the Lorica.- Ultrastructure and Morphogenesis.- Some Unresolved Problems in Morphogenesis.- Phylogeny.- References.- 12. Evolution and Diversity of Form in Radiolaria.- The Quantification of Diversity.- An Appropriate Span of Time.- Diversity Through the Cenozoic.- Nature of the Evolutionary Changes.- Remaining Problems.- References.- 13. Radiolarian Fine Structure and Silica Deposition.- Cytoplasmic Organization.- Skeletal Association with Cytoplasmic Membranes.- Silica and Strontium Sulfate: Phylogenetic Considerations.- References.- Higher Plants.- 14. Ultrastructure of Silica Deposits in Higher Plants.- Procedures.- Silica in the Aerial Organs of Plants.- Silica in Subterranean Organs.- Ultrastructure of Silica Deposits.- Silicon Pathways.- Conclusions.- References.- 15. Silica in Shoots of Higher Plants.- Procedures.- Silica Deposition in Shoots of Equisetum spp.- Silica Deposition in Shoots of Selected Grasses (Poaceae).- Speculations on the Mechanisms of Silica Deposition in Plant Shoots.- References.- Sponges.- 16. Form and Distribution of Silica in Sponges.- Procedures.- Composition of Siliceous Spicules.- Deposition of Siliceous Spicules.- Environmental Influences on Spicules.- Occurrence of Siliceous Spicules in Sponges.- Function of Spicules.- Evolution of Kinds of Spicules in Sponges.- References.- 17. Ultrastructure and Deposition of Silica in Sponges.- Structure of Siliceous Spicules.- Chemistry of Siliceous Spicules.- Formation of Siliceous Spicules.- Developmental and Physiological Aspects of Silica Deposition.- Some Unresolved Questions.- References.- 18. Effects of Germanium on Silica Deposition in Sponges.- Procedures.- Germanium Effects on Sponge Spicules.- Comparison of Effects of Germanium and Silicon.- Interpretation of Germanium Effects.- Complexities of the Sponge Silica Deposition System.- Comparison of Germanium Effects in Sponges and Diatoms.- Specificity of Inhibitory Effects of Germanium.- References.