Short day length-induced decrease of cesium uptake without altering potassium uptake manner in poplar.

Short day length-induced alteration of potassium (K) localization in perennial trees is believed to be a mechanism for surviving and adapting to severe winters. To investigate the relationship between cesium (Cs) and K localizations, a model tree poplar, hybrid aspen T89, was employed. Under short day length conditions, the amount of Cs absorbed through the root and translocated to the root was drastically reduced, but K was not. Potassium uptake from the rhizosphere is mediated mainly by KUP/HAK/KT and CNGC transporters. In poplar, however, these genes were constantly expressed under short-day conditions except for a slight increase in the expression a KUP/HAK/KT gene six weeks after the onset of the short-day treatment. These results indicated that the suppression of Cs uptake was triggered by short day length but not regulated by competitive Cs and K transport. We hypothesize that there are separately regulated Cs and K transport systems in poplar.