Abstract
Plants accumulate silicon in their tissues as amorphous silica. The form of silicon taken up by plants is silicic acid, a neutral molecule that passes through membrane channels with water. After seminal work on rice identified an aquaporin that appeared to mediate the passage of silicic acid, several papers followed and classified similar channels (referred to as “transporters”) in a number of plant species. These channels have been described as essential for silicon uptake and specific for the metalloid. Herein, we critically review the published data on the characterisation of one channel in particular, Lsi1, and identify possible caveats in results and limitations in methods used. Our analysis does not support the suggestion that the identified channels are specific for silicic acid. Computational analyses of the size of the Lsi1 pore additionally suggest that it may not play a significant role in mediating the movement of silicic acid in planta. We suggest that to avoid further confusion, channels currently implicated in the transport of silicic acid in planta are not referred to as silicon-specific transporters. Future research including the use of molecular dynamics simulations will enable the unequivocal identification of channels involved in silicon transport in plants.
Highlights
Silicon is biologically available in soil solution as neutral, monomeric silicic acid
The form of silicon taken up by plants is silicic acid, a neutral molecule that passes through membrane channels with water
After seminal work on rice identified an aquaporin that appeared to mediate the passage of silicic acid, several papers followed and classified similar channels in a number of plant species
Summary
Silicon is biologically available in soil solution as neutral, monomeric silicic acid. The vehicle for its uptake and distribution in plants is water. Silicic acid is a substantially larger molecule than water [1, 2] (Fig. 1). Like water, hydroxyl groups dominate its chemistry and while it has no known organic chemistry and extremely limited inorganic chemistry, it is capable of hydrogen bonding [3]. In following water via the symplastic route,
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