Abstract
Silica is deposited extra- and intracellularly in plants in solid form, as phytoliths. Phytoliths have emerged as accepted taxonomic tools and proxies for reconstructing ancient flora, agricultural economies, environment, and climate. The discovery of silicon transporter genes has aided in the understanding of the mechanism of silicon transport and deposition within the plant body and reconstructing plant phylogeny that is based on the ability of plants to accumulate silica. However, a precise understanding of the process of silica deposition and the formation of phytoliths is still an enigma and the information regarding the proteins that are involved in plant biosilicification is still scarce. With the observation of various shapes and morphologies of phytoliths, it is essential to understand which factors control this mechanism. During the last two decades, significant research has been done in this regard and silicon research has expanded as an Earth-life science superdiscipline. We review and integrate the recent knowledge and concepts on the uptake and transport of silica and its deposition as phytoliths in plants. We also discuss how different factors define the shape, size, and chemistry of the phytoliths and how biosilicification evolved in plants. The role of channel-type and efflux silicon transporters, proline-rich proteins, and siliplant1 protein in transport and deposition of silica is presented. The role of phytoliths against biotic and abiotic stress, as mechanical barriers, and their use as taxonomic tools and proxies, is highlighted.
Highlights
Phytoliths are microscopic amorphous silica structures that are produced within and between plant cells by precipitation and polymerization of silica, and this process is called biosilicification [1].Biosilicification is widespread in the plant kingdom and it has attracted increasing attention in recent years [2]
Some of the plants produce nonsilicaceous phytoliths that are composed of calcium oxalate (CaOX), calcium carbonate, calcium sulphate, calcium phosphate, magnesium oxalate, stronium oxalate, and stronium and barium sulfate
It was previously suggested that xylem loading of Si in rice was mediated by a silicon transporter gene (Lsi6), but by passive diffusion in cucumber suggested that different species have evolved differently [40]
Summary
Phytoliths are microscopic amorphous silica structures that are produced within and between plant cells by precipitation and polymerization of silica, and this process is called biosilicification [1]. Some of the plants produce nonsilicaceous phytoliths that are composed of calcium oxalate (CaOX), calcium carbonate, calcium sulphate, calcium phosphate, magnesium oxalate, stronium oxalate, and stronium and barium sulfate This is not the aspect that we will focus on in this review, and is described elsewhere [3]. Phytoliths provide pieces of evidence for the distribution of taxa or vegetation and help in drawing more reliable inferences regarding palaeovegetation and in reconstructing the palaeoenvironments [5] They can further be used to study their effect on other organisms i.e., grazers, ecosystems, biogeochemical cycles, and changes in the geosphere. We talk about the functional uses of phytoliths in different yet related fields
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