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Effect of calcium, sodium and pH on uptake and accumulation of radiocesium by Riccia fluitans
Heredia, M.A.; Zapico, R.; García-Sánchez, M.J.; Fernández, J.A. (2002). Effect of calcium, sodium and pH on uptake and accumulation of radiocesium by Riccia fluitans. Aquat. Bot. 74(3): 245-256. dx.doi.org/10.1016/s0304-3770(02)00107-9
In: Aquatic Botany. Elsevier Science: Tokyo; Oxford; New York; London; Amsterdam. ISSN 0304-3770, more
Peer reviewed article  

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Keywords
    Accumulation; Caesium; Calcium; P effects; Radioactive contamination; Sodium; Uptake; Riccia fluitans; Fresh water

Authors  Top 
  • Heredia, M.A.
  • Zapico, R.
  • García-Sánchez, M.J.
  • Fernández, J.A., correspondent

Abstract
    The effect of external Ca2+, Na+ and H+ concentrations on radiocesium uptake and concentration factor (CF) was analysed in Riccia fluitans plants grown in K+-deficient and K+-sufficient conditions. The kinetics of the high-affinity K+/Cs+ transporter were also analysed in K+-deficient plants. The K+ regime determined Cs+ uptake rates and CF: both variables were higher in K+-deficient plants than in K+-sufficient plants irrespective of the Ca2+, Na+ or H+ concentrations. The effect of Ca2+ depended on the K+ regime. Cesium uptake rates and CF increased in K+-sufficient plants, 6- and 12-fold, respectively, at decreasing Ca2+ concentrations, whereas the Cs+ uptake rate decreased by 50% in K+-deficient plants and CF showed a maximum at intermediate Ca2+ concentrations (0.1mM). The observed effect of Cs+ uptake rates in K+-deficient plants can be explained by a decrease in the maximum velocity and the affinity of the transporter at low Ca2+ concentrations. Cesium uptake rates decreased by 75% at alkaline pH in K+-deficient plants, as did (by 40%) the maximum velocity of the transporter, while CF reached almost zero values. CF declined by 90% at acid pH but Cs+ uptake rates only decreased by 20% and the maximum velocity of the transporter was relatively constant. Both Cs+ uptake rates and CF showed a maximum at pH 7.5. No significant pH effect was found in K+-sufficient plants. Cesium uptake rates increased by almost three-fold at low Na+ concentrations in both K+ regimes. The increase in uptake rates in K+-deficient plants paralleled the increment in both the maximum velocity of the transporter and its affinity for K+ and Cs+. CF also increased with low Na+ concentrations at both K+ regimes but less so in K+-deficient (three-fold) than in K+-sufficient plants (30-fold). In conclusion, both Cs+ uptake and accumulation would show a maximum in K+-deficient R. fluitans plants in media with neutral pH, very low Na+ and intermediate (0.1mM) Ca2+ concentrations.

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