Fig. 3

Anatomy of L. japonicus nodules. a Mature nodules on a wild type plant, ecotype Gifu. Lenticels (Lc) allowing for air exchange are apparent as white stripes on the nodule surface. The rectangle indicates the plane of a cross section as shown in (b). b Cross section through a wild type nodule. Cells of the nodule centre [57] infected with M. loti bacteria appear pink due to Ruthenium Red staining and co-exist with non-infected cells. The rectangle indicates an excerpt as shown in c. c Close-up of a nodule vascular bundle and lenticel and associated inner and outer nodule cell types. The excerpt is a reproduction of Fig. 4l and shows a section of a GUS-stained nodule expressing pAtS13:GUS with activity in the vascular endodermis (En) and pericycle (Pe). DC Dividing cells, IC infected cell, Pa nodule parenchyma, Lc lenticel, NIC interstitial non-infected cell of the nodule centre, NoC nodule centre, VB vascular bundle, Co outer nodule cortex, Ph phloem cells, Sc sclereid cell layer surrounding the nodule, En vascular endodermis, Pe vascular pericycle, Xy xylem cells. Nomenclature follows Guinel [58], as well as the suggestion of van de Wiel et al. [59] to refer to the inner nodule cortex as nodule parenchyma. Cross sections are 7–8 µm microtome sections of resin (Kulzer Technovit 7100) embedded roots stained with 0.1 % Ruthenium Red. Scale bars a 1 mm; b 50 µm; c 20 µm