The Na + transporter AtHKT1;1 controls retrieval of Na + from the xylem in Arabidopsis

HKT‐type transporters appear to play key roles in Na + accumulation and salt sensitivity in plants. In Arabidopsis HKT1;1 has been proposed to influx Na + into roots, recirculate Na + in the phloem and control root : shoot allocation of Na + . We tested these hypotheses using 22 Na + flux measurements and ion accumulation assays in an hkt1;1 mutant and demonstrated that AtHKT1;1 contributes to the control of both root accumulation of Na + and retrieval of Na + from the xylem, but is not involved in root influx or recirculation in the phloem. Mathematical modelling indicated that the effects of the hkt1;1 mutation on root accumulation and xylem retrieval were independent. Although AtHKT1;1 has been implicated in regulation of K + transport and the hkt1;1 mutant showed altered net K + accumulation, 86 Rb + uptake was unaffected by the hkt1;1 mutation. The hkt1;1 mutation has been shown previously to rescue growth of the sos1 mutant on low K + ; however, HKT1;1 knockout did not alter K + or 86 Rb + accumulation in sos1 .