Accumulation of Silicon in the Monocotyledons Deschampsia caespitosa, Festuca lemanii and Schoenus nigricans

Abstract

Conventional and analytical electron microscopy (EDX, ESI, EELS) were used to investigate the silicon accumulation, the chemical nature of the Si deposits and their formation in three species of monocotyledons. In Deschampsia, in particular parts of the outer epidermal cell wall silicon is accumulated as silicic acid. Electron dense, needle-shaped crystals in the vacuoles of epidermal cells and in the intercellular spaces were also identified as silicic acid. In xylem parenchyma cells, silicon is accumulated as SiO₂, which is formed from Sn silicate. In Festuca, crystal-like deposits of SiO₂ occur on the epidermal surface, in the epidermal and parenchyma cell walls, and in vacuoles of bundle sheath cells. Often the deposits disturb the cell walls and penetrate the envelope of plastids and mitochondria. The crystal-like SiO₂ deposits originate from Sn silicate. In the pericarp of ripe nuts of Schoenus, no stainable cell wall components are detected. The inner part of the pericarp consists of silicic acid, while in the outer regions small clusters of silicic acid are embedded in a matrix of SiO₂. The silicic acid deposits show an unusual, layered structure, typical for lepidoic silicic acids, which consist of two-dimensional crystals lying one above the other.

Key words

SiO₂ - silicic acid - monocotyledons - EDX - ESI - EELS