. 2017 Apr 13;174(2):487–519. doi: 10.1104/pp.16.01949

Table V. Predominant pumps and carriers in the tonoplast of guard cells and their functional characteristics.

Genetic codes relate to Arabidopsis, functional data relate to V. faba unless noted otherwise; for I_sat current, saturation is at V > > 0 for ATPases or V < < 0 for coupled transport; I_V are typical currents within the physiological voltage range and E_rev range with typical gradients of the relevant ionic species; currents were converted where necessary assuming 1 μA cm⁻² = 1 pA pF⁻¹, tonoplast surface area of 2 × 10⁻⁵ cm², and volume of 3 pL. Shorthand identifiers in parentheses cross-reference to Box 1. n.d., not determined. References are as follows: A (Bentrup et al., 1986; Hedrich et al., 1989; Fricker and Willmer, 1990b, 1990a; Davies et al., 1991, 1992, 1994, 1996; Kasamo et al., 1991; Rea and Poole, 1993; Gambale et al., 1994; Ros et al., 1995; Willmer et al., 1995; Obermeyer et al., 1996; Darley et al., 1998; Facanha and de Meis, 1998; Gaxiola et al., 2007); B (Schumaker and Sze, 1986, 1990; Blackford et al., 1990; DuPont et al., 1990; Askerlund and Evans, 1992; Gavin et al., 1993; Askerlund, 1997; Harper et al., 1998; Hirschi, 1999; Palmgren and Harper, 1999; Geisler et al., 2000; Pardo et al., 2006; Pittman, 2011); C (Blumwald and Poole, 1985, 1987; Yamaguchi et al., 2003; Pardo et al., 2006; Rodríguez-Rosales et al., 2009; Chanroj et al., 2011; Barragán et al., 2012; Andrés et al., 2014; Han et al., 2015); D (Accardi and Miller, 2004; De Angeli et al., 2006, 2009a; von der Fecht-Bartenbach et al., 2010; Jossier et al., 2010); E (Burla et al., 2013).

Transporter	Name	Locus	Function	No.	Stoichiometry	I_sat	I_V	E_rev	Ion Selectivity	References
				×10⁶ cell⁻¹		µA cm⁻²	µA cm⁻²	mV
VH⁺-ATPase (VH-ATPase)	VHA-A	AT1G78900	H⁺ uptake, energization	3–8^*	2 H⁺:1 ATP	2^e	1–2^e	−94 to +23	Assumed high H⁺ selective	A
	VHA-B	AT1G76030					3–3.5^a
	VHA-C	AT1G12840					0.6–1^d
	VHA-d	AT3G58730
	VHA-E	AT4G11150
	VHA-F	AT4G02620
	VHA-G	AT3G01390
	VHA-H	AT3G42050
	VHA-a	AT2G28520
	VHA-c	AT4G34720
	VHA-c''	AT4G32530
	VHA-d	AT3G28710
	VHA-e	AT5G55290
VH⁺-PPase (VH-PPase)	AVP1	AT1G15690	H⁺ uptake, energization	6–20^**	1 H⁺:1 PP_i	n.d.	0.6–2.1	−60 to −20		A
	AVP2	AT1G78920
VCa²⁺-ATPase (VCa-ATPase)	ACA4	AT2G41560	Ca²⁺ uptake	0.3–1^***	1 Ca²⁺:1 ATP^****	See I_V	0.01–0.02^c^,^***	−100 to −80	n.d.	B
	ACA11	AT3G57330					0.1^b^,^***
H⁺/Ca²⁺ antiport (CAX)	CAX1	AT2G38170	Ca²⁺ exchange	0.1–0.3^***	3 H⁺:1 Ca²⁺	See I_V	−0.6¹^,^b^,^***	>+100	Assumed selective for Ca²⁺ and H⁺	B
	CAX2	AT3G13320
	CAX3	AT3G51860
	CAX5	AT1G55730
	CAX6	AT1G55720
	CAX7	AT5G17860
H⁺/cation antiport	NHX1	AT5G27150	Cation exchange, pH_i regulation	0.1–0.3^***	1 H⁺:1 K⁺					C
	NHX2	AT3G05030
H⁺/Cl⁻ (NO₃⁻) antiport (CLC)	CLC-B	AT3G27170	Anion exchange	0.3–1^***	1 H⁺:2 Cl⁻	See I_V	0.05–0.1²^,^b	−60 to 0	NO₃⁻>Cl⁻>>SO₄²⁻	D
	CLC-E	AT4G35440			1 H⁺:2 NO₃⁻			−48^b
	CLC-A	AT5G40890
	CLC-C	AT5G49890
ABA transport	ABCC1	AT1G30400	ABA glycosyl ester uptake	n.d.	n.d.	n.d.	n.d.	n.d.	n.d.	E
	ABCC2	AT2G34660	ABA glycosyl ester uptake

Chara corallina.

Arabidopsis.

Brassica oleracea.

Commelina communis.

Beta vulgaris.

> 50 µm [Ca²⁺]_i.

4 mm [NO₃⁻]_i.

Calculated assuming a transport rate of 50 H⁺ s⁻¹, a tonoplast surface area of 2 × 10⁻⁵ cm², and H⁺ flux from Commelina communis (Willmer et al., 1995).

^**

Calculated from current densities assuming a transport rate of 50 H⁺ s⁻¹ (Rea and Poole, 1993) and a tonoplast surface area of 2 × 10⁻⁵ cm².

^***

Calculated from I_sat or the typical transport current assuming a transport turnover rate of 50 s⁻¹ and a guard cell surface area of 3 × 10⁻⁵ cm²; estimates for the Ca²⁺-ATPase are based on assumption of a 10- to 30-fold lower density than the V-type H⁺-ATPase and H⁺-coupled transporters scaled accordingly.

^****

Stoichiometry determined as the minimum thermodynamic requirement to drive net accumulation.