Red, Brown and Green Pigments in Leguminous Root Nodules

Leghemoglobin green derivatives with nitrated hemes evidence production of highly reactive nitrogen species during aging of legume nodules

“…More than 60 y ago, Virtanen and Laine (17) reported the presence in legume nodules of a green pigment similar to animal choleglobin, and proposed that it was generated from Lb through the breaking of the tetrapyrrole ring without the release of Fe. Much more recently, a different type of green proteins was isolated from soybean nodules (22).…”

“…Considerable progress has been made on elucidating the regulatory pathways of Lb biosynthesis (13,14, and references therein), whereas the mechanisms implicated in its degradation are virtually unknown. In animals and plants, the conversion of heme to biliverdins is catalyzed by heme oxygenase (15,16), but can be carried out also nonenzymatically (coupled oxidation) at pH 7.5 in the presence of ascorbate and O 2 (17,18). In plants, biliverdin-like pigments perform important functions in photosynthesis and photomorphogenesis (15) and are also associated with a decrease of N 2 fixation activity and Lb content in senescent nodules (17,19).…”

“…In animals and plants, the conversion of heme to biliverdins is catalyzed by heme oxygenase (15,16), but can be carried out also nonenzymatically (coupled oxidation) at pH 7.5 in the presence of ascorbate and O 2 (17,18). In plants, biliverdin-like pigments perform important functions in photosynthesis and photomorphogenesis (15) and are also associated with a decrease of N 2 fixation activity and Lb content in senescent nodules (17,19). Legume nodule senescence, whether natural or stress-induced, is a complex and poorly studied process, with potential agricultural and ecological relevance as it limits the functional lifespan of nodules, and thereby N 2 fixation (19-21).…”

Consumption of Atmospheric Nitrogen

“…This was confirmed later by Virtanen (1945), who showed its presence to be associated with nitrogenase activity and who, together with Laine, suggested the name "leghemoglobin" (Virtanen and Laine, 1946). Kubo's original idea that leghemoglobin functions in respiratory activity still has so me validity.…”

Nitrogen Metabolism of Higher Plants

“…Later, however, they advanced the view (349) that if amide synthesis is regarded as an expression of the availability, respectively, of oxalacetic and aketoglutaric acids, these being supplied in the course of the respiration of the tissues, wide variations in the behavior of different tissues or of the same tissue under different circumstances become intelligible. This hypothesis has not been subjected to detailed investigation since it is only recently that methods of estimating individual keto acids in plant tissues has received attention (94, 189,196,366368,373,407) . Through the Krebs citric acid cycle, oxalacetic acid and a-ketoglutaric acid are interconvertible and therefore the postulated preferential accumulation of one of these acids implies that different reaction rates obtain for the successive steps in the cycle.…”