A γ-TIP cross-reacting protein is abundant in the cortex of soybean N2-fixing nodules

The distribution and abundance of tonoplast intrinsic protein (gamma-TIP), a putative aquaporin which is abundant in the tonoplast of osmoregulated pulvinus motor cells, were determined in nodules of Glycine max (L.) Merr. using chemical fixation and immunolocalization. This protein was highly expressed in the tonoplast of the inner cortical cells of the nodules but poorly expressed in the vascular transfer cells and in infected cells. It is concluded that the differentiation of the inner cortical cells of the nodules like that of pulvinus motor cells, is accompanied by an increased expression of gamma-TIP. This result is consistent with our previous hypothesis that a reversible exchange of intercellular water by the inner cortical cells plays a role in the regulation of nodule conductance to O-2 diffusion, and hence in subsequent N-2-fixing activity.