Tracer experiment using 42K+ and 137Cs+ revealed the different transport rates of potassium and caesium within rice roots

Abstract

The differences in the transport characteristics in planta between potassium (K+) and caesium (Cs+) was investigated using their radionuclides, 42K+ and 137Cs+. A tracer experiment using nutrient solutions supplemented with 42K and 137Cs revealed that the ratio of the root’s K+ uptake rate to its Cs+ uptake rate was 7–11 times higher than the K+ : Cs+ concentration ratio in the solution, and the number was varied depending on the K concentration in the solution and also on the growth condition. After entering through the root tissues, the 42K+ : 137Cs+ ratio in the shoots was 4.28 times higher than the value in the roots. However, the 42K+ : 137Cs+ ratio in each leaf did not differ significantly, indicating that the primary transport of K+ and Cs+ in the shoots are similarly regulated. In contrast, among the radionuclides stored in the roots over 4 h, 30% of the 42K+ was exported from the roots over the following hour, whereas only 8% of 137Cs+ was exported. In addition, within the xylem, K+ was shown to travel slowly, whereas Cs+ passed quickly through the roots into the shoots. In conclusion, our study demonstrated very different transport patterns for the two ions in the root tissues.

Physiological Verification of the Effect of Potassium Supply on the Reduction of Radiocesium Content in Rice Grain

“…However, their behavior is close but not the same. The ratio of K uptake rate to Cs uptake rate was found to be 7-11 times higher than the ratio of K concentration to Cs concentration in the culture medium, indicating that the root absorbs K selectively over Cs (Kobayashi et al 2015). In addition, K was shown to be selectively relocated to the rice grain over Cs .…”

“…Regarding the determination of the K condition in plants, analyzing the radiocesium distribution among tissues, as well as the K concentration in the soil, is thought to improve the accuracy. If radiocesium concentration is lower in younger tissues than older tissues, the plant is considered to have enough K and thus additional K fertilization would have only minor benefits through the absorption competition as previously reported (Kobayashi et al 2015). In these cases, some other factors influencing radiocesium behavior should be evaluated to reduce the radiocesium contamination.…”

“…The kinetics of K uptake was directly analyzed using 42 K, and simultaneously, the uptake rate of Cs was calculated using 137 Cs. As the K concentration in the uptake medium increased, the K uptake rate increased and the Cs uptake rate decreased (Kobayashi et al 2015). In Arabidopsis plants, the molecule mediating K and Cs uptake has been identified (Qi et al 2008).…”

“…The competition between K uptake and Cs uptake in rice roots is recently described (Kobayashi et al 2015). The kinetics of K uptake was directly analyzed using 42 K, and simultaneously, the uptake rate of Cs was calculated using 137 Cs.…”

Agricultural aspects of radiocontamination induced by the Fukushima nuclear accident — A survey of studies by the Univ. of Tokyo Agricultural Dept. (2011–2016)

“…After entering from the root, the concentration ratio of 42 K + to 137 Cs + in the aboveground parts of the plant, including leaves, was approximately 4 times higher than that in the roots, indicating that there are different transporters for both ions in different tissues. 26) …”