Abstract
Nod-26-like major intrinsic proteins (NIP) in gramineous plants can be divided into three subgroups based on their similarity. Lsi1, which belongs to NIP2 subgroup, has been demonstrating to transport silicon in rice. Here, we compared the permeability of other NIPs to silicic acid by using Xenopus oocytes. Both OsNIP1:1 and OsNIP3:1 did not show transport activity of Si, whereas rice Lsi1 homolog, Lsi6, maize Lsi1 homologs ZmNIP2-1 and 2-2 showed Si transport activity. The substrate specificity of Lsi1 was further characterized by comparing transport activity with three non-charged molecules. Lsi1 showed transport activity for urea and boric acid, but not for glycerol. However the Si transport activity was not or less affected by the presence of equimolar urea or boric acid. The transport activity was inhibited by HgCl2, but not by low temperature treatment. Immunostaining showed that ZmNIP2-1 was localized at the plasma membrane of epidermal cells.
