Root Nodules Of Pea Plants Research Articles

Effects of Pea Aphids (Homoptera: Aphididae) on the Nitrogen Fixing Activity of Bacteria in the Root Nodules of Pea Plants

Different numbers of pea aphids, Acyrthosiphon pisum (Harris), were kept on pea plants, Pisum sativum (L.), bearing root nodules containing the symbiotic bacteria Rhizobium leguminosarum (Frank). Aphid feeding decreased acetylene-reducing activity of the bacteria by as much as 86%, whole plant dry weight up to 74%, nodule weight and number by 77 and 78%, respectively, and nitrogen content of plant tissue by a maximum of 84%. These effects were significant in both young plants 11 days after germination and in more mature plants after pod formation and were proportional to the number of aphids infesting the plants.

Nodule-specific host proteins in effective and ineffective root nodules of Pisum sativum

Nodule-specific root proteins - so called nodulins - were identified in root nodules of pea plants by an immunological assay. Nodulin patterns were examined at different stages of nodule development. About 30 nodulins were detectable during development. Some were preferentially synthesized before nitrogen fixation started, whereas the majority were synthesized concomitantly with leghaemoglobin. Some of the nodulins were located within the peribacteroid membrane. Ineffective Rhizobium strains (a natural nodfix and a pop fix) appeared to be useful in studying the expression of nodulin genes. Synthesis of some nodulins was repressed in ineffective root nodules, indicating that nodulins are essential for the establishment of nitrogen fixation. In both types of ineffective root nodules, leghaemoglobin synthesis was not completely repressed. Low amounts of leghaemoglobin were always detected in young ineffective root nodules whereas in old nodules no leghaemoglobin was present.

Turnover of nitrogenase and leghemoglobin in root nodules of Pisum sativum

Turnover rates of the two nitrogenase components and leghemoglobin in root nodules of pea plants nodulated with Rhizobium leguminosarum were determined with three different methods: 1, Kinetics of 35S incorporation into protein; 2, pulse-chase experiments; 3, chloramphenicol inhibition of bacteroid protein synthesis. Methods 1 and 3 revealed that the turnover rates of the two nitrogenase components and leghemoglobin are identical to the average rate of bacteroid and plant nodule protein turnover. The t 1 2 times of component I and II and leghemoglobin were about 2 days. Pulse-chase experiments with 35SO 2− 4 appeared to be rather unsuitable for determination of turnover rates in pea root nodules.

The Sequence of Appearance of Leghaemoglobin and Nitrogenase Components I and II in Root Nodules of Pisum sativum

The sequence of appearance of nitrogenase components I and II and leghaemoglobin in root nodules of pea plants inoculated with Rhizobium leguminosarum (strain PRE) was studied using radioimmunoassays. Leghaemoglobin was detected before nitrogenase activity. The MoFe component (I) of nitrogenase was detected at the same time as leghaemoglobin, while the Fe component (II) of nitrogenase and nitrogenase activity appeared 1 and 2d later, respectively. The same order of appearance of nitrogenase activity and leghaemoglobin was found in root nodules of cowpea plants inoculated with Rhizobium sp. 32H1.

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

AbstractThe 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.