Role of Silicon in Diatom Metabolism

The in vivo uptake of 31Si‐silicic acid and 68Ge‐germanic acid by cell organelles of Nitzschia alba Lewin and Lewin and Cylindrotheca fusiformis Reimann and Lewin was demonstrated. The organelles were isolated by fractionation of pre‐labeled cells by differential centrifugation in 0.4 M sucrose medium. Electron micrographs showed that the isolated organelles were intact, with the exception of the N. alba mitochondria which appeared swollen and the C. fusiformis chloroplasts which had ruptured outer membranes and lacked stroma material. The amount of 31Si or 68Ge per mg protein of the subcellular fractions decreased in the following general order for both organisms: cell wall, mitochondria, chloroplasts, vesicles, and microsomes. A portion of the 31Si or 68Ge in the organelle fractions could be extracted into a distilled water wash. The uptake of silicon by the organelles suggests that silicon may be involved in some processes of the compartmentalized systems of the cell.