Table 1.

Transport parameters that determine the proton motive force (pmf) for H⁺-mediated symport from the barley leaf apoplast into the cytoplasm of adjacent cells

	Em (mV)	pHcyt	pHapo	[K+]apo (mm)	pmf (mV)
Before oxygen stress	−161 ± 2·73	7·32 ± 0·16	4·88 ± 0·15	2·6 ± 0·13	−305
Hypoxia (20 min)	−159 ± 4·33	6·73 ± 0·21	4·92 ± 0·13	2·8 ± 0·19	−266
Anoxia (20 min)	−81 ± 3·42	6·62 ± 0·15	5·34 ± 0·11	5·5 ± 0·22	−156
Anoxia (2 h)	−65 ± 3·85	6·42 ± 0·13	6·06 ± 0·11	9·9 ± 0·10	−86

E_m, membrane potential as measured in mesophyll cells; pH_cyt, cytoplasmic pH as measured with a pH-sensitive double-barrelled microelectrode; pH_apo, apoplastic pH as measured with a blunt pH-sensitive micro-electrode within the sub-stomatal cavity.

Values given denote average values ± s.e., calculated from five experiments each.

To calculate the pmf, pH gradients (pH_cyt−pH_apo) have been transformed into millivolts: (pH_cyt−pH_apo) × −59 mV.