Silicon uptake and translocation in plants
- Author(s): Ma, Jian Feng
- et al.
Silicon (Si) is the second most abundant element after oxygen in the earth’s crust and shows beneficial effects on plant growth and production by alleviating both biotic and abiotic stresses including diseases, pests, lodging, drought, and nutrient imbalance. Transporters involved in uptake and translocation of Si have been identified in Si-accumulating species including rice, barley and maize. Two kinds of transporters (influx and efflux) are involved in the Si uptake by the roots. The influx transporters (low silicon 1, lsi1) belongs to a Nod26-like major intrinsic protein (NIP) subfamily in aquaporin, while the efflux transporter (Lsi2) belongs to putative anion transporters. They are mainly expressed in the roots. Knockout of either Lsi1 or Lsi2 in rice results in defect of Si uptake, indicating that coupling of Lsi1 with Lsi2 is required for efficient uptake of Si in rice. Although the function of Lsi1 and Lsi2 is similar in rice, barley and maize, they show different expression pattern and cell-type specificity of localization. These differences may explain the differential Si uptake capacity among these species. On the other hand, Lsi6 is localized at the adaxial side of the xylem parenchyma cells in the leaf sheath and leaf blades of rice and maize. Knockout of rice Lsi6 does not affect the uptake of Si by the roots, but results in disordered deposition of silica in the shoots and increased excretion of Si in the guttation fluid, indicating that Lsi6 is a transporter responsible for the unloading of Si from the xylem.