The high affinity K⁺transporter AtHAK5 plays a physiological rolein plantaat very low K⁺concentrations and provides a caesium uptake pathway inArabidopsis

Abstract

Caesium (Cs(+)) is a potentially toxic mineral element that is released into the environment and taken up by plants. Although Cs(+) is chemically similar to potassium (K(+)), and much is known about K(+) transport mechanisms, it is not clear through which K(+) transport mechanisms Cs(+) is taken up by plant roots. In this study, the role of AtHAK5 in high affinity K(+) and Cs(+) uptake was characterized. It is demonstrated that AtHAK5 is localized to the plasma membrane under conditions of K(+) deprivation, when it is expressed. Growth analysis showed that AtHAK5 plays a role during severe K(+) deprivation. Under K(+)-deficient conditions in the presence of Cs(+), Arabidopsis seedlings lacking AtHAK5 had increased inhibition of root growth and lower Cs(+) accumulation, and significantly higher leaf chlorophyll concentrations than wild type. These data indicate that, in addition to transporting K(+) in planta, AtHAK5 also transports Cs(+). Further experiments showed that AtHAK5 mediated Cs(+) uptake into yeast cells and that, although the K(+) deficiency-induced expression of AtHAK5 was inhibited by low concentrations of NH(4)(+) in planta, Cs(+) uptake by yeast was stimulated by low concentrations of NH(4)(+). Interestingly, the growth of the Arabidopsis atakt1-1 mutant was more sensitive to Cs(+) than the wild type. This may be explained, in part, by increased expression of AtHAK5 in the atakt1-1 mutant. It is concluded that AtHAK5 is a root plasma membrane uptake mechanism for K(+) and Cs(+) under conditions of low K(+) availability.

The Effect of a Genetically Reduced Plasma Membrane Protonmotive Force on Vegetative Growth of Arabidopsis

“…Our observation that aha2 mutants with a reduced PMF are more tolerant to cesium toxicity compared with the wild type agrees with previous reports that cesium enters into cells in part through a potassium transporter (Qi et al, 2008;Kanter et al, 2010). The cesium-resistant phenotype of aha2 mutants was observed at a narrow concentration range, 5 to 10 mM, where cesium concentration becomes comparable to potassium concentration in growth medium (one-half-strength MS medium contains approximately 10 mM K + ).…”

Effects of Applying Potassium, Zeolite and Vermiculite on the Radiocesium Uptake by Rice Plants Grown in Paddy FieldSoils Collected from Fukushima Prefecture

“…Since Cs is a group-I alkali metal with chemical properties similar to K, plant roots uptake Cs through the K pathways (Qi et al, 2008). Therefore, the presence of potassium affects the uptake of cesium through the competitive effect in metabolic processes (Zhu and Smolders, 2000).…”

Cesium Accumulation in Paddy Field Rice Grown in Fukushima from 2011 to 2013: Cultivars and Fertilization

“…It is believed that both Cs uptake and transport are mediated by K transporters. In Arabidopsis, one of the KUP/HAK/KT type transporters, AtHAK5, plays a role in non-radioactive cesium ( 133 Cs) absorption under low K conditions (Qi et al 2008). In addition, AtCNGC1 is a candidate gene for determining the natural variation of Cs concentrations (Kanter et al 2010).…”

“…Both K and Cs are alkali metals, and Cs transportation is known to be mediated by several K transporters (Qi et al 2008;Jabnoune et al 2009). Thus, Cs uptake and transportation by K transporters compete with K uptake and transportation in plants.…”