Study on the mechanism of Is uptake and translocation in rice

1)采用^<29>Si核磁共振（NMR）谱法鉴定了木质部汁液中Si的形态。水稻（cv.Oochikara）在含Si 0.5mM的单硅酸溶液中培养，木质部的Si浓度在30 min内达到6mM。在木质部汁液的^<29>Si-NMR光谱中，仅在-72.6 ppm的化学位移处观察到一个信号，这与单硅酸的化学位移一致。对野生型和突变型水稻的木质部液进行的核磁共振分析显示，野生型和突变型水稻对硅的吸收没有显著差异，且木质部液的成分不受硅供应的影响。随着时间的推移，木质部汁液中的Si浓度从初始的18 mM下降到2.6 mM。在含有8mm Si的溶液中加入木质部汁液并不能阻止硅酸的聚合。这些结果表明，硅以单硅酸的形式通过木质部转运，而单硅酸在木质部中的高浓度只是短暂的。2)克隆了水稻中控制硅积累的低硅水稻1号（Lsi1）基因。该基因属于水通道蛋白家族，在根中组成性表达。Lsi1定位于Casperian条带所在的外皮层和内皮层细胞远侧的质膜上。抑制Lsi1表达导致硅摄取减少。此外，Lsi1在爪蟾卵母细胞中的表达仅表现出对硅的转运活性。3)分离到一个新的硅吸收缺陷突变体。与野生型相比，该突变体对硅的吸收较低，但对氮、磷、钾等其他矿物质的吸收没有差异。定位结果表明，导致突变的基因位于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.