The Effect of Darkness on the Leghemoglobin Content and Amino Acid Levels in the Root Nodules of Pea Plants

Abstract

The dependence of the nitrogen fixing system in the root nodules of pea plants (Pisum sativum) L. cv. Torsdag II) on light induced reactions was studied. The pots of the inoculated pea plants, after the nolules had fixed nitrogen for a fornight, were transferred to a dark room. The control plants were kept under normal lighting conditions. The decay of leghemoglobin was measured after photosynthesis had ceased. In the dark the red nodules turned green in three days, when about half of the haem had been broken down. The plants in normal lighting conditions had maintained the red nodules. The appearence of leghemoglobin and bacteroids was simultaneouos. In normal lighting conditions the number of bacteroids was about 1.6 × 108 per g fresh nodules. The appearance of leghemoglobin and bacteroids was simultaneous. In normal lighting conditons the number of bacteroids was bout 1.6 × 108 per g fresh nodules. At the same time as the nodules turned green in the dark most of the bacteroids disappeared and the number of rod‐shaped bacteria increased. After five days int the dark thenumber of bacteria of the green nodules was 2.2 × 108 per g fresh nodules. A large increase of of bacteria in the nodules is one of the results after the termination of effective symbiosis. Quantitative estimations were made with an automatic amino acid analysator of the amino acid composition in the root nodules of pea plants grown in the light and of pea plants grown in the dark. Altogether 27 amino acids and amides and 3 unknown ninhydrin positive compounds were found in the free amino acid fraction. In the red N‐fixing nodules asparagine, the amide of aspartic acid, was the most prominent (more than 50 per cent of the total amino acid fraction), indicating the energy charge of the nitrogen fixation. 5 days in the dark affected the proportions of the amino acids as follows. Asparagine, homoserine, γ‐aminobutyric acid and ethanolamine were decreased and the most of the others increased. In the hydrolysate of the non‐soluble protein fraction 25 amino acids could be detected. The proportions of the amino acids in the root nodules of light‐grown and dark‐grown pea plants were very similar. Hydroxyproline and α, γ‐diaminopimelic acid (DAP) were found in these fraction. Most of the DAP was contained in the peptide fraction. Also hydroxyproline was found to a small extent. It was assumed that the amino acids in this fraction were derived from the peptides of both plant cells and rhizobia.

Aging in Legume Symbiosis. A Molecular View on Nodule Senescence in Medicago truncatula

“…Senescence in nodules is visible by a color shift in the nitrogen-fixing zone from pink, associated with the functional leghemoglobin protein, to green, associated with the degradation of its heme group (Roponen, 1970). At the ultrastructural level, changes in the symbiosomes and cellular organelles are observed: The cytoplasm becomes less electron dense (Andreeva et al, 1998) and vesicles and ghost membranes appear as a result of host and symbiosome membrane disintegration (Timmers et al, 2000).…”

Bacteroids Are Stable during Dark-Induced Senescence of Soybean Root Nodules

“…Immunoblots of bacteroid extracts revealed the presence of nitrogenase component II in control, 4-day dark-stressed, and 8-day dark-stressed plants that were Studies of the effects of imposed stress on nodulated plants have provided much information on the changes taking place in whole nodules. There is rapid attenuation of nitrogenase activity (AR activity), with subsequent declines in total nodule protein and Lb levels (3,7,18,20,22,29). However, corresponding data on bacteroid status are incomplete.…”

“…There is rapid attenuation of nitrogenase activity (AR activity), with subsequent declines in total nodule protein and Lb levels (3,7,18,20,22,29). However, corresponding data on bacteroid status are incomplete.…”

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

“…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).…”