Silicon deposition in higher plants

Abstract

Silicification is reported in the Pteridophyta and the Spermatophyta, including gymnosperms and angiosperms. Dicotyledon families containing Si accumulators of considerable agricultural significance include the Fabaceae, Cucurbitaceae and Asteraceae. Among the monocotyledons, the Cyperaceae and Poaceae (Gramineae) are pre-eminent. Silica deposits, commonly called phytoliths, occur in cell walls, cell lumens or in extracellular locations. These deposits frequently possess a characteristic morphology revealing their tissue and taxonomic origin. Silicification occurs in roots and the shoot including leaves, culms and in grasses, most heavily in the inflorescence. Deposits occur in epidermal, strengthening, storage and vascular tissues. Biogenic silica structure is affected by ambient physico-chemical conditions mediated by tissue maturation, pH, ionic concentrations and cell wall structure, as illustrated by the results of a developmental study of silicification in wheat seedlings. Silicified tissues provide support and protection and may also sequester toxic metals, as illustrated by our recent work on the codeposition of aluminum with silicon in cereals and conifers. Some phytoliths have been implicated as carcinogens. Phytoliths are being increasingly used in archaeology as many retain their morphology in sediments. © 2001 Elsevier B.V. All rights reserved.