Table 2. Nitrogenase activities of nodule infected by S. meliloti CCNWSX0020 or dmeF mutant under Co²⁺ or Ni²⁺ stress.

Bacterial strain	Nodule fresh weight (mg plant−1)			Nitrogenase activity (nmol h−1 plant−1)			Nitrogenase activity (nmol h−1 [mg nodule mass]−1)
	0 mg/kg NiCl2	50 mg/kg NiCl2	100 mg/kg NiCl2	0mg/kg NiCl2	50 mg/kg NiCl2	100 mg/kg NiCl2	0 mg/kg NiCl2	50 mg/kg NiCl2	100 mg/kg NiCl2
Wild-type strain dmeF mutant	5.32 ± 0.5a 4.84 ± 0.8a	4.30 ± 0.4a 2.72 ± 0.5a	3.99 ± 0.5a 2.28 ± 0.3b	54.31 ± 4.1a 48.78 ± 4.7a	42.24 ± 3.9a 30.50 ± 3.2b	41.88 ± 4.5a 23.64 ± 3b	9.96 ± 1.7a 9.91 ± 1.1a	9.53 ± 1.5a 11.03 ± 1.4a	10.28 ± 1.6a 10.09 ± 1.4a
	0 mg/kg CoCl2	50 mg/kg CoCl2	100 mg/kg CoCl2	0 mg/kg CoCl2	50 mg/kg CoCl2	100 mg/kg CoCl2	0 mg/kg CoCl2	50 mg/kg CoCl2	100 mg/kg CoCl2
Wild-type strain dmeF mutant	5.14 ± 0.5a 4.91 ± 0.8a	3.82 ± 0.4a 2.50 ± 0.5a	2.60 ± 0.5a 1.88 ± 0.3b	52.22 ± 5a 50.08 ± 4.9a	38.06 ± 3.6a 28.99 ± 3.2b	30.41 ± 3.5a 18.32 ± 3.1b	10.11 ± 1.6a 10.18 ± 1.4a	9.95 ± 1.3a 11.2 ± 1.4a	11.53 ± 1.2a 9.57 ± 1.3a

Notes.

The values indicate the means ± standard error of triplicate samples.

The letters a/b are significant difference (p < 0.05) from plants inoculated with S. meliloti CCNWSX0020 or dmeF mutant under nickel or cobalt stress conditions.