title: Theoretical model of the effect of potassium on the uptake of radiocesium by rice.
abstract: After the accident at the Fukushima Dai-ichi Nuclear Power Plant owned by Tokyo Electric Power Company on 11 March 2011, potassium was applied to fields in the Tohoku and Kanto areas of Japan to reduce radiocesium uptake by crops. Despite the intense studies relating to the effect of potassium application on availability of radiocesium in the soil, physiological changes of radiocesium uptake by crops in response to K(+) concentration around roots remains elusive. In the present study, we developed physiological models describing the effect of K(+) on the uptake of radiocesium by rice. Two Cs(+):K(+) competition models were evaluated using a wide range of data obtained from pot and field experiments: the model assuming a uniformity in the gene expression of K(+) transporter (Model I) and the model assuming the increase in the gene expression of K(+) transporter in response to K(+) concentration below threshold (Model II). The root-mean-square deviation between the measured and estimated values was larger in Model I than in Model II. Residuals were positively correlated with K(+) in Model I but showed no deflection in Model II. These results indicate that Model II explains the effect of K(+) on the uptake of radiocesium better than Model I. Model II may provide the appropriate countermeasures in inhibiting the transfer of radiocesium from soil to crop. The effect of changes in the variables in Model II on the relationship between available K(+) in soil and (137)Cs uptake by plant was simulated. An increase in available (137)Cs(+) in soil enhanced the response of (137)Cs uptake to K(+). The effects of Michaelis-Menten constant for Cs(+) were the inverse of the (137)Cs(+) effect. The effect of Michaelis-Menten constant for K(+) showed the same tendency as that of (137)Cs(+), but the effect was much less than that of (137)Cs(+). An increase in the threshold of K(+) below which the gene expression of K(+) transporter increases enhanced the response of (137)Cs uptake to K(+) in the high-K(+) range.
authors.affiliation: Fukushima Agricultural Technology Centre, 116 Shimonakamichi, Takakura-Aza, Hiwada-machi, Koriyama, Fukushima 963-0531, Japan. Electronic address: fujimu@affrc.go.jp.
authors.forename: Shigeto
authors.initials: S
authors.lastname: Fujimura
authors.affiliation: NARO Institute of Crop Science, Tsukuba, Ibaraki 305-8518, Japan. Electronic address: junkoi@affrc.go.jp.
authors.forename: Junko
authors.initials: J
authors.lastname: Ishikawa
authors.affiliation: Fukushima Agricultural Technology Centre, 116 Shimonakamichi, Takakura-Aza, Hiwada-machi, Koriyama, Fukushima 963-0531, Japan. Electronic address: sakuma_yuuki_01@pref.fukushima.lg.jp.
authors.forename: Yuuki
authors.initials: Y
authors.lastname: Sakuma
authors.affiliation: Fukushima Agricultural Technology Centre, 116 Shimonakamichi, Takakura-Aza, Hiwada-machi, Koriyama, Fukushima 963-0531, Japan. Electronic address: saito_takashi_01@pref.fukushima.lg.jp.
authors.forename: Takashi
authors.initials: T
authors.lastname: Saito
authors.affiliation: Fukushima Agricultural Technology Centre, 116 Shimonakamichi, Takakura-Aza, Hiwada-machi, Koriyama, Fukushima 963-0531, Japan. Electronic address: satou_mutsuto_01@pref.fukushima.lg.jp.
authors.forename: Mutsuto
authors.initials: M
authors.lastname: Sato
authors.affiliation: Fukushima Agricultural Technology Centre, 116 Shimonakamichi, Takakura-Aza, Hiwada-machi, Koriyama, Fukushima 963-0531, Japan. Electronic address: yoshioka_kunio_01@pref.fukushima.lg.jp.
authors.forename: Kunio
authors.initials: K
authors.lastname: Yoshioka
mesh_terms: D002586:Cesium / Q000378:metabolism*; D002588:Cesium Radioisotopes / Q000378:metabolism*; D008954:Models, Biological; D012275:Oryza / Q000378:metabolism*; D018517:Plant Roots / Q000378:metabolism; D011188:Potassium / Q000378:metabolism*; D011834:Radiation Monitoring; D012987:Soil / Q000737:chemistry; D012990:Soil Pollutants, Radioactive / Q000378:metabolism*
chemical_list: D002588:Cesium Radioisotopes; D012987:Soil; D012990:Soil Pollutants, Radioactive; D002586:Cesium; D011188:Potassium
keywords: Competition; Model; Potassium transporter; Radiocesium; Rice; Uptake