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The effect of soil exchangeable potassium (K) and cesium (Cs) levels on Cs uptake and accumulation in different parts of rice (Oryza sativaL.) plants were examined using paddy soils with diverse exchangeable K and Cs in pot experiments. Aboveground Cs uptake decreased with higher exchangeable K and was linearly correlated with exchangeable Cs/K ratios, indicating competitive absorption of these elements by roots. Variation in Cs concentration in brown rice among soils was also related to the exchangeable Cs/K ratio. The exchangeable Cs/K ratio was positively reflected in the Cs/K concentration ratio in each plant part, with a specific slope, suggesting that Cs transport was coordinated with K transport and that there were regulated discriminations of Cs against K in the translocation process among parts. The Cs/K ratio was higher in brown rice and dead leaves than in active leaves, stems and husks. The distribution of Cs accumulation in brown rice was 14.5% on average, but it was variable and negatively related to K concentration in the stem. The Cs distribution in aboveground plant parts also decreased with higher K concentration in the root. These results imply the importance of the competitiveness with K in the root absorption and translocation of Cs within the plant. Based on the observed relationship between Cs and K, effective K management and other measures to control Cs accumulation in plant parts are discussed. [ABSTRACT FROM PUBLISHER]

Pot and field experiments were conducted to clarify the effect of soil exchangeable potassium (K) and cesium-137 (137Cs) on137Cs accumulation and to establish soil index in rice (Oryza sativaL.). Four paddy soils in Fukushima Prefecture, Japan, showing different transfer factors for radioactive Cs derived from the accident of Fukushima Daiichi Nuclear Power Station in the field were compared in terms of137Cs accumulation in rice in a pot experiment.137Cs accumulation in shoots and brown rice widely varied among soils with the transfer factor ranging from 0.018 to 0.068 for shoots and 0.004 to 0.065 for brown rice.137Cs concentration in brown rice and shoots tended to decrease with higher levels of soil exchangeable K, and they were more closely related to the exchangeable Cs/K ratio. Similar relationships between the Cs/K ratio and Cs accumulation in plants were obtained for the stable isotope cesium-133 (133Cs). The distributions of137Cs and133Cs in grains were also similar and variable among soils. The transfer factors obtained in pot experiments mostly agreed with field observations. The results imply that the exchangeable137Cs/K can be a potential soil index to estimate137Cs accumulation in rice. [ABSTRACT FROM PUBLISHER]

Potassium (K) is an important macronutrient together with nitrogen and phosphorous. Potassium mostly accumulates in the internodes of rice plants during ripening stage. Since internodes are responsible for translocation of carbohydrates to the grains during ripening, the involvement of internode K in grain yield has been suggested, however, the precise mechanism remains unclear. This study aims to examine the relationship between rice grain yield in different cultivars and the dynamics of K and non-structural carbohydrates (NSC) in the internodes during the ripening period. Field experiments were conducted to investigate the differences in the dynamics of K and NSCs in internodes from heading to maturation in 10 cultivars with different yields and three mutants with different grain numbers. To reveal the localization of K in internode tissues, we conducted laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analysis. During the early ripening period from heading to 14 days after heading (14 DAH), the decrease in NSC contents in lower internodes was higher in the high-yielding indica cultivars than in japonica cultivars. In the late ripening period from 14 DAH to maturing, re-accumulation of NSC in lower internodes was higher in the japonica than in the indica. In contrast, the increase in K contents in the internodes was larger in the indica than in the japonica throughout the ripening stage. In the internodes of low-yielding whole crop silage (WCS) cultivar, the NSC contents were maintained at high levels during ripening, while K contents were consistently low. Similar results were observed in the mutant with low grain numbers. The mutant had lower K contents and higher NSC contents than the wild type (WT). Correlation analysis of different cultivars indicated that the change in K content in whole internodes from heading to maturing was negatively correlated with the change in NSC content. LA-ICP-MS analysis of internode tissues of the indica cultivar revealed that K accumulated more in the parenchyma cells than in large vascular bundles. These results suggest that K accumulation in the internodes is positively correlated with NSC translocation from internodes to grains, which could be through indirect effect of K accumulation in parenchyma on enhancement of long distance transport of NSC from internodes to the grains. This study provides new insights into the mechanism underlying the role of K in grain filling, which would help improving usage of K fertilizer for optimum plant growth and yields. • High-yielding rice cultivars translocate large amount of NSC from internodes to grains. • Potassium is highly accumulated in internodes of the high-yielding cultivars during ripening. • Cultivar difference in potassium accumulation is positively correlated with NSC translocation. • Potassium accumulates mostly in the parenchyma cells of internodes. • Potassium accumulation in internodes may enhance transport of NSC from internodes to grains. [ABSTRACT FROM AUTHOR]