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. 2010 Mar 4;5(3):e9519. doi: 10.1371/journal.pone.0009519

Figure 1. Nodule structure and infection in wild type and Fix− mutants.

Figure 1

Semi-thin longitudinal nodule sections were stained with toluidine blue and observed by light microscopy. (A) J5-Sm1021 Wild type; (B) TRV43-Sm1021; (C) J5-Sm1021bacA; (D) TR3-Sm1021; (E) V1-Sm1021. (Left panels) Tissue organisation of nodules including a corresponding schematic illustration. Tissues distinguishable in the nodule are I, meristem; I* in (E), primordium-like structure with dividing cells; II, infection and differentiation zone; II* in (D), zone of infection without cellular differentiation; III, nitrogen fixation zone; III* in (B), zone with fully differentiated cells that, however, do not fix nitrogen; III** in (C), zone with differentiated plant cells in which bacteroids are not differentiated; IV, zone of symbiotic cell senescence; root and nodule cortical tissues are in grey. Bars equal 200 µm. (Middle panels) Enlargement of the central area of the nodules showing the presence or absence of differentiated symbiotic cells. Bars equal 50 µm. (Right panels) Images of symbiotic cells showing the structure of the intracellular bacteria (A–C) or the absence of differentiation and bacteria in the cells in the central area of the nodule (D,E). Bars equal 50 µm.