Signal enhancement of protein binding by electrodeposited gold nanostructures for applications in Kretschmann-type SPR sensors.

We propose a novel Kretschmann-type surface plasmon resonance (SPR) sensor chip having a surface covered with electrodeposited gold nanostructures to enhance the sensitivity of SPR biosensing. The nanostructure is three-dimensional and has a larger surface area than a conventional flat surface chip, which increases the amount of protein binding and also induces a large change in the effective dielectric constant of the sensing area. The gold nanostructures were formed by electrodeposition under galvanostatic conditions, so their size could be controlled by manipulating the deposition time and current. The sensing characteristics, including the concentration dependence and noise level, indicated that the performance of the resulting chip (called a Au-black chip) was equivalent to that of a conventional sensor chip. We also determined the optimal electrodeposition conditions to obtain a sharp SPR curve for protein detection assay; the optimal thickness of the gold layer was 50-60 nm. Enhanced protein sensing was demonstrated by using a binding assay of anti-BSA antibody and BSA molecules. The protein binding signal was several times higher than that of the conventional assay. The insights into electrodeposition for SPR sensing presented here will enable improved sensitivity for detecting low-concentration and small proteins.

Genotypic difference in silicon uptake and expression of silicon transporter genes in rice.

Rice (Oryza sativa) is a highly silicon (Si)-accumulating species that shows genotypic differences in Si accumulation. We investigated the physiological and molecular mechanisms involved in the genotypic difference in Si uptake between the japonica var. Nipponbare and the indica var. Kasalath. Both the Si concentration in the shoot and the Si uptake per root dry weight were higher in Nipponbare than in Kasalath grown in either soil or nutrient solution. The Si uptake by a single root was also higher in Nipponbare than in Kasalath. A kinetics study showed that Nipponbare and Kasalath had a similar K(m) value, whereas the V(max) was higher in Nipponbare. The expression of two Si transporter genes (Low silicon rice 1 [Lsi1] and Lsi2) investigated using real-time reverse transcription polymerase chain reaction revealed higher expression of both genes in Nipponbare than in Kasalath. Immunostaining with Lsi1 and Lsi2 antibodies revealed a similar pattern of subcellular localization of these two Si transporters in both varieties; Lsi1 and Lsi2 were localized at the distal and proximal sides, respectively, of both exodermis and endodermis of the roots. These results revealed that the genotypic difference in the Si accumulation results from the difference in abundance of Si transporters in rice roots.

An efflux transporter of silicon in rice.

Silicon is an important nutrient for the optimal growth and sustainable production of rice. Rice accumulates up to 10% silicon in the shoot, and this high accumulation is required to protect the plant from multiple abiotic and biotic stresses. A gene, Lsi1, that encodes a silicon influx transporter has been identified in rice. Here we describe a previously uncharacterized gene, low silicon rice 2 (Lsi2), which has no similarity to Lsi1. This gene is constitutively expressed in the roots. The protein encoded by this gene is localized, like Lsi1, on the plasma membrane of cells in both the exodermis and the endodermis, but in contrast to Lsi1, which is localized on the distal side, Lsi2 is localized on the proximal side of the same cells. Expression of Lsi2 in Xenopus oocytes did not result in influx transport activity for silicon, but preloading of the oocytes with silicon resulted in a release of silicon, indicating that Lsi2 is a silicon efflux transporter. The identification of this silicon transporter revealed a unique mechanism of nutrient transport in plants: having an influx transporter on one side and an efflux transporter on the other side of the cell to permit the effective transcellular transport of the nutrients.

A silicon transporter in rice.

Silicon is beneficial to plant growth and helps plants to overcome abiotic and biotic stresses by preventing lodging (falling over) and increasing resistance to pests and diseases, as well as other stresses. Silicon is essential for high and sustainable production of rice, but the molecular mechanism responsible for the uptake of silicon is unknown. Here we describe the Low silicon rice 1 (Lsi1) gene, which controls silicon accumulation in rice, a typical silicon-accumulating plant. 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 exodermis and endodermis cells, where casparian 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. The identification of a silicon transporter provides both an insight into the silicon uptake system in plants, and a new strategy for producing crops with high resistance to multiple stresses by genetic modification of the root's silicon uptake capacity.

Characterization of the silicon uptake system and molecular mapping of the silicon transporter gene in rice.

Rice (Oryza sativa L. cv Oochikara) is a typical silicon-accumulating plant, but the mechanism responsible for the high silicon uptake by the roots is poorly understood. We characterized the silicon uptake system in rice roots by using a low-silicon rice mutant (lsi1) and wild-type rice. A kinetic study showed that the concentration of silicon in the root symplastic solution increased with increasing silicon concentrations in the external solution but saturated at a higher concentration in both lines. There were no differences in the silicon concentration of the symplastic solution between the wild-type rice and the mutant. The form of soluble silicon in the root, xylem, and leaf identified by (29)Si-NMR was also the same in the two lines. However, the concentration of silicon in the xylem sap was much higher in the wild type than in the mutant. These results indicate that at least two transporters are involved in silicon transport from the external solution to the xylem and that the low-silicon rice mutant is defective in loading silicon into xylem rather than silicon uptake from external solution to cortical cells. To map the responsible gene, we performed a bulked segregant analysis by using both microsatellite and expressed sequence tag-based PCR markers. As a result, the gene was mapped to chromosome 2, flanked by microsatellite marker RM5303 and expressed sequence tag-based PCR marker E60168.

Characterization of silicon uptake by rice roots.

• Rice (Oryza sativa) is a typical Si-accumulating plant and it has been suggested that it has a specific uptake system for silicic acid in the roots. • Here, we characterized this specific system in rice roots. The ability of rice roots to take up Si was much higher than that of other gramineous species. • A kinetic study indicated that Si uptake was mediated by a type of proteinaceous transporter; the Km value was estimated to be 0.32 mm, suggesting that the transporter had a low affinity for silicic acid. Si uptake increased linearly with time, but pretreatment with Si did not affect the uptake of Si, suggesting that the system for Si uptake was not inducible. Mercuric chloride and phloretin, significantly inhibited Si uptake, but 4,4'-diisothiocyanato-stilbene-2,2'-disulfonic acid (DIDS) did not. Mercuric chloride and phloretin also inhibited water uptake, but to a lesser extent. Si uptake was unaffected by the presence of boric acid. • Taken together, the data indicate that the uptake of Si by rice roots is a transporter-mediated process and this transporter contains Cys residues but not Lys residues.

A rice mutant defective in Si uptake.

Rice (Oryza sativa) accumulates silicon (Si) in the tops to levels up to 10.0% of shoot dry weight, but the mechanism responsible for high Si uptake by rice roots is not understood. We isolated a rice mutant (GR1) that is defective in active Si uptake by screening M(2) seeds (64,000) of rice cv Oochikara that were treated with 10(-3) M sodium azide for 6 h at 25 degrees C. There were no phenotypic differences between wild type (WT) and GR1 except that the leaf blade of GR1 remained droopy when Si was supplied. Uptake experiments showed that Si uptake by GR1 was significantly lower than that by WT at both low and high Si concentrations. However, there was no difference in the uptake of other nutrients such as phosphorus and potassium. Si concentration in the xylem sap of WT was 33-fold that of the external solution, but that of GR1 was 3-fold higher than the external solution at 0.15 mM Si. Si uptake by WT was inhibited by metabolic inhibitors including NaCN and 2,4-dinitrophenol and by low temperature, whereas Si uptake by GR1 was not inhibited by these agents. These results suggest that an active transport system for Si uptake is disrupted in GR1. Analysis of F(2) populations between GR1 and WT showed that roots with high Si uptake and roots with low Si uptake segregated at a 3:1 ratio, suggesting that GR1 is a recessive mutant of Si uptake.