Plant Colonization and in vitro endoglucanase activity of Wt and ∆ nifK mutants. (A) and (B): An optical section of root tissue infected of Wt R4-368 at 7 and 20 DAI respectively. (C) and (D): An optical section of root tissue infected of Wt R4-368 ΔnifH at 7 and 20 DAI respectively. (E) and (F) are the mock-inoculated control showing no GFP signal. Scale bars (bar, 20 μm) are shown in each image. Mc: microcolony; Rh: root hair; Ag: cell aggregates; IC: intercellular colonization. (G) and (H): Congo-red stained KM agar plate without and with glucose respectively.