Table 1.

Nitrogenase activity in wild-type M. truncatula and in the nodulation mutants, sickle and domi. domi is a non-nodulating mutant of M. truncatula that is resistant to infection by Rhizobium (10). Nitrogenase activity was determined by the acetylene reduction assay (27), where nitrogenase enzyme reduces substrate acetylene to ethylene. Acetylene reduction was measured on nine roots for each genotype, 19 days after inoculation with Rhizobium.

GenotypeNitrogenase activity (pmol ethylene min−1 root−1 ± SE)
A17 (wild type)120 ± 70
sickle (hypernodulating)220 ± 70
domi (non-nodulating)0.3 ± 0.3