Fig. 6.
Symbiotic phenotype of cyo. (a) Nitrogenase activity of intact nodulated roots whose nodules harboured wild-type or cyo at 8 days p.i. Error bars indicate sd (n = 8; P<0.05). Acetylene reduction activity = [(ethylene peak/acetylene peak)/nodule weight]. (b) Gus-staining of nodules harbouring gus-tagged wild-type (CE426) and gus-tagged cyo mutants (CE607) at different days p.i. The gusA gene was constitutively expressed at equivalent levels (in TY culture) in both strains under low (0.1 % O2) and high (21 % O2) oxygen conditions. Therefore, staining reflects the relative density of bacterial cells. Bars in the lower right corner of each image represent 500 µm. Samples are from 6, 7, 8 and 10 days p.i.