Effects of nitrogen on cesium allocation in rice plants (Oryza sativa)

After the nuclear accident in Fukushima Prefecture, Japan in 2011, Cesium (Cs) contaminated nearby agricultural regions. Studies in these rice fields found that low potassium (K) and high nitrogen (N) fertilizer application enhanced Cs uptake in rice shoot organs. However, the influence of root and soil physics in these findings, as well as precise nutrient levels, remain to be clarified. We sought to analyze these relationships utilizing hydroponically grown rice plants. The rice plants were subjected to various concentrations of K and N nutrient solutions. We measured Cs allocation within the plants and performed transcript analyses using root tissues. Under low-K conditions, low-N plants accumulated less Cs in shoots and more in roots when compared to control-N conditions, even though overall Cs uptake remained unchanged. Expression analyses of root mRNAs showed that low-N plants accumulated reduced levels of OsAKT1 mRNA, encoding K transporter. We also found a negative relationship between shoot Cs and K status at control-N levels but not in low-N conditions. Our results suggest that the application of N shifts Cs from roots into the shoots and that OsAKT1 in root vascular tissues influence Cs allocation. As a practical matter, fine tuning N/K application and the targeted breeding of K transporters have the potential to mitigate Cs contamination in rice plants.