Abstract
Silicon is taken up by rice in the form of a non-charged molecule, silicic acid (H4SiO4). However, the form of Si for translocation in the xylem is unknown. The loading process of Si into the xylem was characterized and the translocation form of Si was identified by using 29Si-NMR. When rice (cv. Oochikara) was exposed to a solution containing 0.5mM Si, the Si concentration in xylem reached as high as 6mM after only 30 min. Kinetic study showed that loading of Si into the xylem was mediated by a kind of transporter (Km 0.33mM). Only one signal at chemical shift of -72ppm was observed in the xylem sap, indicating that Si is translocated in the form of monosilicic acid. Si concentration in the xylem sap in vitro decreased with time to a certain level (2.6mM), suggesting that the existence of monosilicic acid at high concentration in the xylem is transient.
