Table II. Electrophysiological responses of barley and Arabidopsis root cells to sudden NH₄⁺ withdrawal with or without Ca(NO₃)₂.

One-week-old barley seedlings and 5-week-old Arabidopsis plants were grown on full nutrient medium supplemented with high NH₄⁺ (2 mm in Arabidopsis, 10 mm in barley) and 0.0225, 0.1125, or 5 mm K⁺. ΔΨ_m measurements were taken from root epidermal and cortical cells 2 to 3 cm from the root tip, and the AWE ± Ca(NO₃)₂ (5 mm in barley) was measured. Letters denote significantly different means (P < 0.05; one-way ANOVA with Bonferroni post hoc test), and asterisks denote different levels of significance between control and treatment pairs (**0.001 < P < 0.01; Student’s t test); ns, not significant. Error values indicate se of four replicates. n.d., Not determined.

Species	Genotype	[K+]ext	ΔΨm
			Control	AWE	AWE ± Ca(NO3)2
		mm	mV
Barley	Metcalfe (wild type)	0.0225	−143.6 ± 2.7a	−202.6 ± 21.7b	−251.4 ± 13.0c
		0.1125	−136.2 ± 3.0a	−189.3 ± 8.9b	−208.5 ± 10.0b
		5	−133.2 ± 2.2a	−164.6 ± 5.1b	−149.0 ± 8.0b
Arabidopsis	Col-0	0.0225	−165.0 ± 13.7	−231.0 ± 8.1**	n.d.
	WS		−137.6 ± 7.2	−172.9 ± 21.5ns	n.d.
	atakt1		−139.2 ± 3.5	−192.4 ± 8.3**	n.d.
	athak5		−106.1 ± 8.6	−156.6 ± 22.2ns	n.d.
	athak5 atakt1		−258.0 ± 22.9	−265.3 ± 20.8ns	n.d.