. 2013 Oct 14;14(10):20359–20385. doi: 10.3390/ijms141020359

Table 2.

List of all HKT2 transporters isolated and characterized.

Transporter	Expression in planta	Ref.	Function in planta	Ref.	Transport selectivity when heterologous expressed	Ref.
OsHKT2;1	In the roots: epidermis, exodermis, cortex differentiated into aerenchyma, stele (mainly in the phloem); In the leaves: bulliform cells, xylem, phloem, mesophyll cells	[22]	Nutritional Na⁺ uptake from the external medium	[11]	Na⁺ and K⁺ transport (Xenopus oocytes)	[22,30,31]
					Na⁺ transport (S. cerevisiae cells)	[18,30]
					K⁺ transport (S. cerevisiae cells)	[31]
OsHKT2;2	Expressed only in the roots	[32]	Na⁺/K⁺ symporter in BY2 tobacco cells	[33]	Na⁺, K⁺, (S. cerevisiae and Xenopus oocytes)	[30,34]
OsHKT2;2	Expressed only in the roots	[32]	Expected to co-transport both Na⁺ and K⁺ in conditions of K⁺ starvation	[32]	Na⁺, K⁺, (S. cerevisiae and Xenopus oocytes)	[30,34]
OsHKT2;2/1	Expressed only in the roots	[32]	Expected to co-transport both Na⁺ and K⁺ in the roots in conditions of low K⁺ and under salt stress	[32]	Na⁺ and K⁺ transport (S. cerevisiae cells and Xenopus oocytes)	[32]
OsHKT2;3	Marginally expressed in the roots in comparison to the shoots	[34]			No currents or uptake observed in Xenopus oocytes or S. cerevisiae cells	[34]
OsHKT2;4	Vasculature of primary/ lateral root cells, leaf sheaths, spikelets and the base of stems. Expressed also in mesophyll cells	[35]	Possible role in K⁺ homeostasis as a K⁺ transporter/channel	[34]	Permeable to NH4⁺, Li⁺, Na⁺, K⁺, Ca²⁺, Mg²⁺ Zn²⁺, Mn²⁺, Cu²⁺, Fe²⁺, Cd²⁺ (Xenopus oocytes)	[35]
			Possible redundant role in planta as oshkt2;4 mutants show no phenotype	[35]	Permeable to Na⁺, K⁺, Mg²⁺, Ca²⁺ (Xenopus oocytes)	[34]
				[35]	K⁺ transport (S. cerevisiae cells)	[34]
			Proposed to function as a K⁺ transporter involved in both nutritional K⁺ uptake and long-distance K⁺ transport	[36]	Na⁺ and K⁺ transport (Xenopus oocytes)	[36]
TaHKT2;1	Root cortical and stele cells Vascular tissue of mesophyll cells	[14]	Na⁺ uptake from the external medium	[37]	Permeable to Na⁺, K⁺, Cs⁺ and Rb⁺ (Xenopus oocytes)	[14]
					K⁺ transport (S. cerevisiae cells)	[14]
					Na⁺ and K⁺ transport (S. cerevisiae cells)	[38,39]
					Na⁺ and K⁺ transport (Xenopus oocytes)	[38,39]
					Permeable to Na⁺, K⁺ and Mg⁺ (Xenopus oocytes)	[34]
PutHKT2;1	Mainly in roots	[40]	Possible high affinity K⁺ transporter	[40]	Na⁺ and K⁺ transport (S. cerevisiae cells)	[40]
HvHKT2;1	Root cortex, leaf blades and leaf sheaths	[41,42]	Possible involvement in the root K⁺ (re)absorption at very low K⁺ concentrations	[41,42]	Na⁺ and K⁺ transporter (S. cerevisiae and Xenopus oocytes)	[41–43]
HvHKT2;1	Root cortex, leaf blades and leaf sheaths	[41,42]	Possible uptake of Na⁺ in the roots	[41,42]		[41–43]
PhaHKT2;1	Roots and shoots	[44]			Na⁺ and K⁺ transport (S. cerevisiae cells)	[40,44]
PpHKT1	-------	-------			Na⁺ and K⁺ uptake (S. cerevisiae cells)	[45]