. 2016 Jul 5;7:992. doi: 10.3389/fpls.2016.00992

Table 1.

Summary for K⁺ and Na⁺ uptake features observed in Arabidopsis and rice roots.

Species	Cation	Type of uptake^†	K_m (μM)	Sensitivity	Transport systems involved	Reference
Arabidopsis	K⁺	High-affinity	24^∗	(-) NH₄⁺, Ba⁺², Cs⁺ (=) Ca⁺²	AtHAK5, AKT1	Spalding et al., 1999; Gierth et al., 2005; Rubio et al., 2008; Coskun et al., 2013
		Low-affinity	3,991^∗	(-) Ba⁺², Cs⁺, TEA, La⁺³, Na⁺ (=) NH₄⁺, Ca⁺²	AKT1	Spalding et al., 1999; Gierth et al., 2005; Caballero et al., 2012

	Na⁺	High-affinity	n.d.	n.d.	–	–
		Low-affinity	Linear response	(-) Ca⁺², Ba⁺², cyclic-nucleotides (+) La⁺³, GABA (=) TEA, Cs⁺	–	Maathuis and Sanders, 2001; Essah et al., 2003

Rice	K⁺	High-affinity	11–18	(-) NH₄⁺	OsHAK1, OsHAK5, OsAKT1	Bañuelos et al., 2002; Li et al., 2014; Yang et al., 2014; Chen et al., 2015
		Low-affinity	n.d.	n.d.	OsHAK1, OsAKT1	Li et al., 2014; Chen et al., 2015

	Na⁺	High-affinity	60 or 477–655^¶	(-) K⁺, Ba⁺²	OsHKT2;1	Garciadeblas et al., 2003; Horie et al., 2007; Haro et al., 2010
		Low-affinity	n.d.	(=) K⁺, Ca²⁺	OsHKT2;1	Horie et al., 2007; Malagoli et al., 2008

^†High-affinity uptake takes into account cation uptake observed at external concentrations <0.5 mM while the low-affinity one does so at >0.5 mM. ^∗Obtained with Rb⁺ as an analog for K⁺. (+), (-), and (=) stand for activation, inhibition, or no effect on cation uptake, respectively. n.d., not determined. ^¶ Only one component was identified in Horie et al. (2007) for external Na⁺ concentrations up to 5 mM.