Localization of glutamine synthetase isoforms in hair cells of Azolla leaves

Immunoelectron microscopy and a quantitative analysis of immunogold labeling of a glutamine synthetase (GS; EC 63.1.2) revealed that, in mesophyll cells of mature leaves of Azolla filiculoides, almost all GS was present in chloroplasts. By contrast, in hair cells, abundant labeling of GS was observed both in chloroplasts and in the cytoplasm. In hair cells of cyanobiont-free plants, the labeling of GS of both chloroplasts and cytoplasm was very weak compared to that of cyanobiont-containing plants. The findings suggest that hair cells play an important role in the assimilation of ammonia released by the cyanobiont.