Three types of hemoglobins exist in higher plants, symbiotic, non-symbiotic, and truncated hemoglobins. Symbiotic (class II) hemoglobins play a role in oxygen supply to intracellular nitrogen-fixing symbionts in legume root nodules, and in one case ( Parasponia Sp.), a non-symbiotic (class I) hemoglobin has been recruited for this function. Here we report the induction of a host gene, dgtrHB1, encoding a truncated hemoglobin in Frankia-induced nodules of the actinorhizal plant Datisca glomerata. Induction takes place specifically in cells infected by the microsymbiont, prior to the onset of bacterial nitrogen fixation. A bacterial gene (Frankia trHBO) encoding a truncated hemoglobin with O (2)-binding kinetics suitable for the facilitation of O (2) diffusion ( ) is also expressed in symbiosis. Nodule oximetry confirms the presence of a molecule that binds oxygen reversibly in D. glomerata nodules, but indicates a low overall hemoglobin concentration suggesting a local function. Frankia trHbO is likely to be responsible for this activity. The function of the D. glomerata truncated hemoglobin is unknown; a possible role in nitric oxide detoxification is suggested.
- soybean root-nodules
- nitrogenase activity
- oxygen diffusion
- symbiotic hemoglobin
Pawlowski, K., Jacobsen, K. R., Alloisio, N., Denison, R. F., Klein, M., Tjepkema, J. D., Winzer, T., Sirrenberg, A., Guan, C., & Berry, A. M. (2007). Truncated hemoglobins in actinorhizal nodules of Datisca glomerata. Plant Biology, 9(6), 776-785. https://doi.org/10.1055/s-2007-965258