Scanning Electron Microscopy of Silica Deposition in the Leaves of Barley (Hordeum sativum L.)

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Abstract
Deposits of silicon in the leaves of Hordeum sativum L. (cv. Deba Abed) have been investigated by means of the scanning electron microscope. The opaline structures have been studied within epidermal and other cells as well as in isolation after a drastic nitric and perchloric acid treatment. The main types occur as costal rods and intercostal ‘hats’, but in addition, prickle hairs are occasionally silicified as well as certain sclerenchyma, mesophyll and xylem elements. Bulliform cells are rarely silicified in barley. Detailed descriptions are given of the various deposits viewed with the SEM. The shapes conform with what is revealed by a similar examination of the leaf surface. In some cases, the silica deposits are associated with the cell walls, but in vessels it can be deposited on the inner side of the wall and the lumen can become infilled. In such cases the pits are seen as raised ‘pads’ aligned with those of adjacent elements. It is suggested that two distinct processes may be involved according to whether the secondary wall becomes impregnated or whether the lumina became filled with silica. In the former, considerable proportions of silica may be deposited after the secondary wall is formed, whereas in the latter, it appears that the wall, which cannot resist a drastic treatment, is relatively free of silica.

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