## 3 Results and Discussion  
### The Paddy Field Tests  
Activity concentrations of \({}^{134}\)Cs and \({}^{137}\)Cs in the soils of the test and reference paddies were corrected to the date of 15 March 2011. The corrected \({}^{134}\)Cs to \({}^{137}\)Cs activity ratios of the test and reference paddies were 1:1.01 and 1:1.04, respectively, and very similar to the activity ratio of 1:1 emitted from the Fukushima accident by reactor units 1, 2, and 3 [16]. Activity concentrations of \({}^{134}\)Cs, \({}^{137}\)Cs, and their sums in the soil attached to the root, straw, hull, bran, and polished rice harvested from the test and reference paddy fields are given in Table 1.  
The sums of activity concentrations of \({}^{134}\)Cs and \({}^{137}\)Cs in the straw, hull, bran, and polished rice of the reference paddy field are approximately 19, 31, 15, and 35 times higher than the corresponding parts from the test paddy field. The results suggest that the PSC was effective in preventing, though not completely, the transfer of \({}^{134}\)Cs and \({}^{137}\)Cs from the soil into various parts of the rice plant. It should be noted that the sum of activity concentrations of \({}^{134}\)Cs and \({}^{137}\)Cs in the polished rice from the test paddy field was 30 Bq-kg\({}^{-1}\), a level well below the Japanese governmental safeguard value of 100 Bq-kg\({}^{-1}\).  
According to [PERSON] and [PERSON] [17], the molecular mechanisms for the influx of K\({}^{+}\) and Cs\({}^{+}\) ions into roots are the same. There are many K\({}^{+}\)-transporting proteins (channels) in the plasma membrane of root cells in plants, aiding the permeation of Cs\({}^{+}\) across the root cells. These channels are as follows:  
1. KIRC (inward-rectifying K\({}^{+}\) channels), which is inhibited by Cs\({}^{+}\) and Ca\({}^{2+}\)[18].
2. KORC (outward-rectifying K\({}^{+}\) channels), which is uninhibited by extracellular Ca\({}^{2+}\), Cs\({}^{+}\), or quinine [19].
3. VICC (voltage-insensitive cation channels), which is inhibited by Ca\({}^{2+}\) in the soil solution [20].
4. KUP (high-affinity K\({}^{+}\)/H\({}^{+}\) transporter), which is highly permeable to K\({}^{+}\) and Rb\({}^{+}\) and possibly also permeable to Na\({}^{+}\) and Cs\({}^{+}\)[21].
5. HACC (hyperpolarization-activated Ca\({}^{2+}\) channels), which is selective for Ba\({}^{2+}\) \(>\) Ca\({}^{2+}\) = Mg\({}^{2+}\) \(>\) Mn\({}^{2+}\) but inhibited by submillimolar Al\({}^{3+}\)[22].
6. DACC (depolarization-activated Ca\({}^{2+}\) channels), which is permeable to Ca\({}^{2+}\), Ba\({}^{2+}\), Sr\({}^{2+}\) and Mg\({}^{2+}\)[23].  
Since PSC was mixed with the soil of the test paddy field and because calcium, magnesium, barium, and aluminum exist in the PSC (Table 2), it is expected that all the KIRC, KORC, VICC, and HACC would not be activated. Therefore, the KUP and DACC are the only possible channels responsible for radiocesium detected in various parts of the rice plant. On the other hand, because the reference paddy field is deficient in calcium, magnesium, barium, and aluminum from the PSC, the rice harvested from it would have a higher radiocesium content than those from the test paddy field (Table 1).  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \multirow{2}{*}{**Constituents**} & \multicolumn{2}{c}{**Test Paddy Field with PSC (Bq-kg\({}^{-1}\))**} & \multicolumn{2}{c}{**Reference Paddy Field (Bq-kg\({}^{-1}\))**} \\ \cline{2-7}  & \({}^{134}\)Cs & \({}^{137}\)Cs & \({}^{134}\)Cs + \({}^{137}\)Cs & \({}^{134}\)Cs & \({}^{137}\)Cs & \({}^{134}\)Cs + \({}^{137}\)Cs \\ \hline Soil (\({}^{1}\)) & 23,353 \(\pm\) 66 & 22,499 \(\pm\) 63 & 45,852 \(\pm\) 91 & 23,668 \(\pm\) 68 & 23,481 \(\pm\) 66 & 47,149 \(\pm\) 90 \\ Straw (\({}^{2}\)) & 96 \(\pm\) 2 & 135 \(\pm\) 3 & 231 \(\pm\) 4 & 1970 \(\pm\) 13 & 2370 \(\pm\) 15 & 4340 \(\pm\) 20 \\ Hull (\({}^{2}\)) & 53 \(\pm\) 1 & 78 \(\pm\) 2 & 131 \(\pm\) 3 & 1880 \(\pm\) 13 & 2260 \(\pm\) 14 & 4140 \(\pm\)