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. 2013 Sep 13;4:359. doi: 10.3389/fpls.2013.00359

FIGURE 1.

FIGURE 1

Longitudinal cross section of the determinant soybean nodule (A), compared to a longitudinal cross section of the indeterminant M. truncatula nodule (B). The determinant soybean nodule consists of a central infected region (IR), composed of infected cells (ICs; dark) dispersed between uninfected cells (UCs; light); surrounding the IR is the inner cortex (IC), which includes the vascular bundles surrounded by parenchyma cells; the outer cortex (OC), encapsulates the nodule. The meristem of the indeterminant M. truncatula nodule remains active throughout nodule development, allowing continual growth. As a result the nodule is divided into sequential zones of development, including the meristem (M); invasion zone (IZ), where rhizobia infect divided cortical cells; a transition zone (TZ), composed of infected cells containing differentiating bacteria; a nitrogen fixation zone (NFZ) and a zone of senescence (SZ) close to the root. Images courtesy of Aleksandr Gavrin.