Structure and localization of silica in the leaf and internodal epidermal system of the marsh grass Phragmites australis

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Abstract
Silica deposition sites in the epidermal system of shoots of P. australis were analyzed by scanning electron microscopy and nondispersive X-ray microanalysis, as well as by acid digestion of leaf and stem tissue. In the lamina adaxial and abaxial epidermal layers, silica is concentrated in the stomatal guard cells, silica cells and outer tangential walls of long epidermal cells, but little silica occurs in the trichomes. In the sheath, both epidermal surfaces are highly silicified, in effect, providing a silicified jacket around the internode. Pulvini of both the sheath and internode possess less silica than nonpulvinar regions above them. The silica in Phragmites is viewed as providing support for the shoot system (particularly in the sheaths), protecting the plant against predators and water loss and, possibly, allowing more light to pass through the epidermal system via the silica cells to the photosynthetic mesophyll tissue that lies below the epidermal system in both lamina and sheath.