Fig. 4.

Wild‐type‐like pink nodules formed on Medicago nin knockout mutant (nin‐1) roots transformed with truncated NIN_ΔPB1. Pink nodules formed on nin‐1 roots transformed with ProNIN_3C‐5kb:NIN_ΔPB1 at 4 wk post inoculation (wpi) (a). Semithin sections of the nodules stained with toluidine blue display normal zonation (b). Confocal image of nodules formed on the ProNIN_3C‐5kb:NIN_ΔPB1 transgenic nin‐1 roots at 4 wpi with a rhizobial strain carrying nifH:GFP showed that nifH is highly expressed in the fixation zone (c). Close‐up of nodule cells in fixation zone, showing well developed symbiosomes (d). M, meristem; IF, infection zone; FX, fixation zone; S, symbiosome. Bars: (a) 2 mm; (b) 300 µm; (c) 250 µm; (d) 30 µm.