[74] Leghemoglobins

Abstract

This chapter discusses leghemogloblins. The O2-binding hemoproteins of legume root nodules are variously described as leghemoglobins or legoglobins. They occur in the infected cells of legume root nodules with an overall concentration of 1–3 mg leghemoglobin (Lb) per gram fresh weight, depending on the plant species. Their distribution within the infected cell is still controversial; evidence from autoradiography and diaminobenzidine staining suggests that they are restricted to the membrane envelope around the bacteroids. Ferritin-labeled antibody techniques suggest their location in the plant cytoplasm. Genetically, leghemoglobins are coded for by the plant DNA, as shown by the production of dissimilar leghemoglobins by dissimilar plants infected with the same Rhizobium. Leghemoglobin synthesis begins very shortly after nodule initiation, usually before nitrogenase synthesis can be demonstrated. It is restricted to the infected cells of the nodule. In legumes with meristematic nodules, leghemoglobin synthesis continues in proportion to nodule growth; in nodules lacking meristems, leghemoglobin synthesis occurs only over a brief period of nodule formation, and the concentration remains more or less constant until nodule senescence. In this chapter, plant growth, isolation, storage, cell-free synthesis, and properties of leghemogloblins are also discussed in detail. © 1980, Academic Press, Inc.