Microscopic analysis of nodules and infection threads formed by
R. etli wild-type (A, C, and
E) and casA mutant FAJ1805 (B, D,
F, and G) strains. (A and
B) Toluidine blue stainings of 3-μm-thick sections of
P. vulgaris nodules. (C–F) Transmission
electron micrographs of 3-week-old nodules. (G) GusA
staining of FAJ1806 bacteria expressing a casA–gusA
fusion inside the infection threads. Black arrowhead, plant plasma
membrane; white arrowhead, symbiosome membrane; black arrow, infection
thread (IT); b, bacteroid; SS, symbiosome space; v, vesicle.