Table III.

Free-energy values (mV) for the uptake of K⁺ by H⁺ or Na⁺ symport mechanisms into expanding cells of seminal roots of barley plants growing in FNS containing 2 μm K⁺ for various times

		Na+:K+ (1:1)		Na+:K+ (1:2)
Plant Age	H+:K+ (1:1)	1 mm Na+	20 mm Na+	1 mm Na+	20 mm Na+
d
7	−102	−14	+61	+118	+194
9	−99	−17	+59	+112	+189
14	−84	−8	+68	+125	+201
16	−57	+7	+83	+144	+220
21	−59	+5	+81	+140	+216

The values were calculated using Equation 1 and assumed two different cytosolic Na⁺ concentrations of 1 and 20 mm. Negative values indicate that the mechanism could maintain the observed trans-plasma membrane K⁺ gradient.