Table I. Effect of stirring and buffering with complexes on uptake of Cd by four plant species, at a Cd²⁺ concentration of 1 nm.

The 4-h uptake (in nmol per g root fresh weight [RFW] per hour) was determined in solutions with 2 mm Ca(NO₃)₂, 2 mm MES (pH 6.0), 15 μm H₃BO₃ in absence or presence of complexes of different dissociation rate. The total ligand concentration, [L_tot], and the ratio of total Cd concentration to the free Cd²⁺ concentration (1 nm), [Cd_tot]/[Cd²⁺], in the solution is specified in the table. se of n replicates between brackets. y, Solution stirred; n, solution unstirred during the uptake period.

Liganda	[Ltot]	[Cdtot]/[Cd2+]	Stirred	Spinach		Rapeseed		T. caerulescens		Wheat
				n	Cd uptake	n	Cd uptake	n	Cd uptake	n	Cd uptake
	mm				nmol (g RFW)−1 h−1		nmol (g RFW)−1 h−1		nmol (g RFW)−1 h−1		nmol (g RFW)−1 h−1
–		1	n	6	0.070 (0.009)	12	0.051 (0.007)	2	0.170 (0.008)	2	0.078 (0.001)
–		1	y	13	0.239 (0.018)	17	0.114 (0.012)	3	1.17 (0.17)	2	0.093 (0.004)
NTA	0.10	100	n	3	4.55 (0.49)	3	2.08 (0.52)	2	6.24 (0.41)
NTA	0.30	310	n	3	11.2 (1.1)	3	5.91 (0.46)	2	14.5 (1.7)
NTA	1.0	1,260	n	3	26.2 (1.3)	3	12.1 (1.8)	2	28.2 (3.7)
NTA	3.0	5,700	n	2	39.3 (8.1)	3	32.5 (4.4)	2	72.6 (10.0)
NTA	4.9	10,000	n	2						2	7.22 (2.08)
HEDTA	0.029	10,000	n	3	8.25 (0.81)	2	16.5 (0.7)	2	24.8 (8.9)	2	2.37 (0.32)
CDTA	0.014	10,000	n	2	1.62 (0.23)	2	4.13 (0.03)	2	11.5 (1.5)	2	1.15 (0.45)

^aDissociation rate constant, k_d, of the Cd-ligand complex: >10⁻², 10^−2.8, and 10⁻⁵ s⁻¹ for NTA, HEDTA, and CDTA, respectively.