A possible mechanism of biological silicification in plants

Exley, Christopher

doi:10.3389/fpls.2015.00853

Cited by 142 publications

(107 citation statements)

References 40 publications

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“…Once the solubility of Si(OH) 4 is exceeded (i.e. > 2 mM), SiO 2 polymerization occurs and, for cells, this can be toxic (Iler, ; see also Montpetit et al ., ; Exley, ); thus, it stands to reason that Si(OH) 4 transported through healthy root cells (via Lsi1 and Lsi2) must maintain a cytosolic concentration of < 2 mM, although direct cytosolic measurements are currently lacking. The majority of Si is found polymerized in the apoplast (e.g.…”

Section: Silicon Transport In Plants: To Absorb or Not To Absorbmentioning

confidence: 99%

The controversies of silicon's role in plant biology

et al. 2018

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Contents Summary 67 I. Introduction 68 II. Silicon transport in plants: to absorb or not to absorb 69 III. The role of silicon in plants: not just a matter of semantics 71 IV. Silicon and biotic stress: beyond mechanical barriers and defense priming 76 V. Silicon and abiotic stress: a proliferation of proposed mechanisms 78 VI. The apoplastic obstruction hypothesis: a working model 79 VII. Perspectives and conclusions 80 Acknowledgements 81 References 81 SUMMARY: Silicon (Si) is not classified as an essential plant nutrient, and yet numerous reports have shown its beneficial effects in a variety of species and environmental circumstances. This has created much confusion in the scientific community with respect to its biological roles. Here, we link molecular and phenotypic data to better classify Si transport, and critically summarize the current state of understanding of the roles of Si in higher plants. We argue that much of the empirical evidence, in particular that derived from recent functional genomics, is at odds with many of the mechanistic assertions surrounding Si's role. In essence, these data do not support reports that Si affects a wide range of molecular-genetic, biochemical and physiological processes. A major reinterpretation of Si's role is therefore needed, which is critical to guide future studies and inform agricultural practice. We propose a working model, which we term the 'apoplastic obstruction hypothesis', which attempts to unify the various observations on Si's beneficial influences on plant growth and yield. This model argues for a fundamental role of Si as an extracellular prophylactic agent against biotic and abiotic stresses (as opposed to an active cellular agent), with important cascading effects on plant form and function.

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Section: Silicon Transport In Plants: To Absorb or Not To Absorbmentioning

confidence: 99%

The controversies of silicon's role in plant biology

et al. 2018

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“…In most cases, the deposition of silica in roots cannot rely on evaporation of water for concentrating silicic acid. A passive mode of silicification in roots thus assumes that Si condensation occurs as water is absorbed by the symplasm, leaving behind concentrated silicic acid solution in the apoplasm (Exley, 2015). Such separation may occur at the Casparian bands, where the passive diffusion of Si and water is blocked (Sakurai et al, 2015).…”

Section: Sites Of Silicification In Grassesmentioning

confidence: 99%

“…The first is based on a passive mode of silicification, relying on the spatial correlation between silica deposition and organ transpiration (Yoshida et al, 1962; Sangster and Parry, 1971; Rosen and Weiner, 1994; Euliss et al, 2005). In this case, specific cell wall components and cuticular structures may additionally affect the location of bio-silicification (reviewed by Exley, 2015; Guerriero et al, 2016). This hypothesis infers that silica deposition in plants is a spontaneous process resulting from auto-condensation of Si molecules as the sap undergoes dehydration (Yoshida et al, 1962).…”

Section: Introductionmentioning

confidence: 99%

Silicification in Grasses: Variation between Different Cell Types

2017

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Plants take up silicon as mono-silicic acid, which is released to soil by the weathering of silicate minerals. Silicic acid can be taken up by plant roots passively or actively, and later it is deposited in its polymerized form as amorphous hydrated silica. Major silica depositions in grasses occur in root endodermis, leaf epidermal cells, and outer epidermal cells of inflorescence bracts. Debates are rife about the mechanism of silica deposition, and two contrasting scenarios are often proposed to explain it. According to the passive mode of silicification, silica deposition is a result of silicic acid condensation due to dehydration, such as during transpirational loss of water from the aboveground organs. In general, silicification and transpiration are positively correlated, and continued silicification is sometimes observed after cell and tissue maturity. The other mode of silicification proposes the involvement of some biological factors, and is based on observations that silicification is not necessarily coupled with transpiration. Here, we review evidence for both mechanisms of silicification, and propose that the deposition mechanism is specific to the cell type. Considering all the cell types together, our conclusion is that grass silica deposition can be divided into three modes: spontaneous cell wall silicification, directed cell wall silicification, and directed paramural silicification in silica cells.

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“…All plants take up silicic acid (Si(OH) 4 ) via their roots and transport it throughout the tissues following water [1]. However, not all plants deposit Si(OH) 4 as biogenic silica to the same degree with some plants such as Equisetum (horsetails) being considered as silica accumulators with as much as 5% of their tissue dry weight being attributed to biological silicification [2].…”

Section: Introductionmentioning

confidence: 99%

Callose-associated silica deposition in Arabidopsis

Brugière

Exley

2017

Journal of Trace Elements in Medicine and Biology

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The mechanism of biological silicification in plants remains to be elucidated. There are strong arguments supporting a role for the plant extracellular matrix and the -1-3-glucan, callose, has been identified as a possible template for silica deposition in the common horsetail, Equisetum arvense. The model plant Arabidopsis thaliana, which is not known as a silica accumulator, can be engineered to produce mutants in which, following a pathogenassociated molecular pattern challenge, callose production in leaves is either induced

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A possible mechanism of biological silicification in plants

Cited by 142 publications

References 40 publications

The controversies of silicon's role in plant biology

The controversies of silicon's role in plant biology

Silicification in Grasses: Variation between Different Cell Types

Callose-associated silica deposition in Arabidopsis

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