Advances in The Uptake and Translocation of Silicon in Plants

Silicon exerts beneficial effects on plant growth and development by alleviating biotic and abiotic stresses. The uptake and translocation of Si in plants is mediated by Si transporters, recently, several genes encoding Si transporters have been identified from rice, barley and maize. OsLsi shows polar localization in root tissues, OsLsi1 is localized at the plasma membrane of both exodermis and endodermis on the distal side in rice roots, where Casparian strips exist; OsLsi2 is localized on the proximal side of the same cells. Therefore, OsLsi1 is responsible for transport of Si from the external solution to the root cells, whereas OsLsi2 is an efflux transporter responsible for the transport of Si from the exodermal cells to the apoplast of aerenchyma; Si is transported into the stele by OsLsi 1 and OsLsi2 coordination and then translocated to the shoot by transpirational flow through the xylem. OsLsi6 was observed in the xylem parenchyma cells that were adjacent to vessels in both leaf sheaths and leaf blades besides roots, which is responsible for the export of Si from the xylem and for the subsequent distribution of Si. In maize and barley, Si is taken up from the external solution by the influx transporter (ZmLsi1/HvLsi1) localized on the distal side of cells in the epidermis and cortex layer, and then transferred to the endodermis through the symplastic pathway. At the endodermis, Si is released by an active Si efflux transporter (ZmLsi2/HvLsi2) to the stele. In addition, ZmLsi6 has the similar the localization and transport activity with OsLsi6 and might have similar functions, however, the Lsi6 in barley is not identified until now. More researches in the mechanism of Si transport in plant are needed further.