Study on the mechanism of Is uptake and translocation in rice

1)木质部汁液中Si的形式通过~ 13 <29>Si-核磁共振（NMR）光谱鉴定。在含0.5mM硅的单油酸溶液中培养的水稻（cv.Oochikara），木质部中的硅浓度在30分钟内达到6 mM。在<29>木质部汁液的~ 13 Si-NMR谱中，仅在化学位移为-72.6ppm处观察到一个信号，这与单油酸的化学位移一致。木质部汁液的^1H-NMR研究表明，硅吸收缺陷的野生型水稻和突变体水稻之间没有任何显著差异，木质部汁液的成分不受硅供应的影响。体外木质部汁液中的Si浓度随时间从初始的18 mM降低到2.6 mM。将木质部汁液添加到含有8 mM Si的溶液中并不能阻止柠檬酸的聚合。这些结果表明，硅在木质部中以单油酸的形式转运，并且单油酸浓度在木质部中只是短暂的高浓度。2）克隆了一个控制硅在水稻中积累的基因--低硅水稻1号（Lsi 1）。该基因属于水通道蛋白家族，在根中组成型表达。Lsi 1定位于外皮层和内皮层细胞远端侧的质膜上，Casperian带位于此处。抑制Lsi 1表达导致硅摄取减少。此外，在爪蟾卵母细胞中表达的Lsi 1仅表现出对硅的转运活性。3）分离到一个新的硅摄取缺陷突变体。与野生型相比，该突变体表现出较低的Si吸收，但在其他矿物质如N、P和K的吸收方面没有任何差异。定位结果表明，该突变基因位于3号染色体上。

1)The form of Si in xylem sap was identified by ^<29>Si-nuclear magnetic resonance (NMR) spectroscopy. In rice (cv.Oochikara) cultured in a monosilicic acid solution containing 0.5mM Si, the Si concentration in the xylem reached 6mM within 30 min. In the ^<29>Si-NMR spectra of the xylem sap, only one signal was observed at a chemical shift of -72.6 ppm, which is consistent with that of monosilicic acid. An ^1H-NMR study of xylem sap did not show any significant difference between the wild-type rice and mutant rice defective in Si uptake, and the ingredient of the xylem sap was not affected by the Si supply. The Si concentration in the xylem sap in vitro decreased from an initial 18 mM to 2.6 mM with time. Addition of xylem sap to a solution containing 8 mM Si did not prevent the polymerization of silicic acid. All these results indicate that Si is translocated in the form of monosilicic acid through the xylem and that the concentration of monosilicic acid is high in the xylem only transiently.2)A gene, Low silicon rice 1 (Lsi1), controlling silicon accumulation in rice, a typical silicon-accumulating plant, was cloned. This gene belongs to the aquaporin family and is constitutively expressed in the roots. Lsi1 is localized on the plasma membrane of the distal side of both the exodermis and endodermis cells, where Casperian strips are located. Suppression of Lsi1 expression resulted in reduced silicon uptake. Furthermore, expression of Lsi1 in Xenopus oocytes showed transport activity for silicon only.3)A novel mutant defective in Si uptake was isolated. This mutant showed lower Si uptake compared to the wild type, but there is no any difference in the uptake of other minerals such as N,P, and K. Mapping result showed that the gene responsible for the mutation is located on the chromosome 3.