T. Laine

Investigations on the root nodule bacteria of leguminous plants: XX. Excretion of nitrogen in associated cultures of legumes and non-legumes

The associated growth of peas and different non-legumes (barley, oats, wheat, and potato) was investigated both under sterile conditions and in ordinary pot cultures. In the former case the medium consisted of quartz sand, and in the latter of clay or sandy loam soil, poor in soluble nitrogen. It is shown that nitrogen was transferred from the pea nodules to the non-legumes. In sterile cultures, where the excreted amino-acids cannot undergo decomposition, oats, wheat and barley utilized only a part of the excreted nitrogen, generally less than 50 per cent. In some instances, however, the barley took up considerably over 50 per cent of the excreted nitrogen. There was an apparent accumulation of aspartic acid in the medium of the associated cultures. In pot cultures, where the amino-acids may have been broken down by contaminating micro-organisms, the transfer of the excreted nitrogen to the potato exceeded 90 per cent. All experiments show that with increasing ratio of non-legumes to legumes the growth of the peas suffers, obviously from lack of nitrogen. Under these conditions, the excretion from the nodules increases to such an extent that the peas receive only a small fraction of the nitrogen fixed by the nodules. The major part of the carbohydrate material furnished by the pea for the amino-acid synthesis in the nodules is excreted into the medium. This naturally causes disturbances in the growth of the pea.

Biological Synthesis of Amino Acids from Atmospheric Nitrogen

SYMBIOTIC nitrogen fixation in leguminous root nodules proceeds, according to our conception, in the following manner:

Chemical Nature of the Amino Acids excreted by Leguminous Root Nodules

SOME years ago we showed conclusive evidence that considerable amounts of nitrogenous compounds appear in the medium in inoculated, but otherwise sterile, cultures of leguminous plants. Since then we have tried to isolate these nitrogenous compounds and to determine their chemical nature. The nitrogen compounds were extracted from the quartz sand with water and found to consist chiefly of amino acids. Amino nitrogen determinations according to van Slyke—the reaction mixture being shaken for 30 minutes—showed that 87–98 per cent of the total nitrogen was amino nitrogen. The amino nitrogen values varied to some extent in different extracts.

Investigations on the root nodule bacteria of leguminous plants: XIX. Influence of various factors on the excretion of nitrogenous compounds from the nodules

1. It has been shown experimentally that the excretion of nitrogen noted by us in cultures of inoculated legumes takes place from the nodule bacteria, probably from the intranodular ones, and not from the roots. No excretion of amino acids occurs in cultures of uninoculated legumes growing on nitrate nitrogen. 2. Our earlier hypothesis that the legumes receive their nitrogen nutrition from the nodules in the form of organic nitrogen compounds, particularly amino acids, is in perfect accord with our new observations concerning the process of excretion. All facts indicate that the amino acids concerned are primary products of the nitrogen fixation, and not breakdown products of proteins. Bonds valuable work along quite different lines produced results which support this conclusion. He, however, did not study the chemical nature of the nitrogen compounds in question. 3. The excretion of nitrogen occurs in media capable of absorbing the excreted nitrogen compounds (cellulose, kaolin, sand, soil). The demonstration of the excretion is not possible in water cultures except when very large quantities of water are used. On the basis of these facts a hypothesis is advanced to explain the nature of the excretion. 4. The term total fixed nitrogen has been used as an expression for the extent of nitrogen fixation, while the term extent of excretion is employed to indicate that percentage of the total fixed nitrogen which is excreted from the nodules. 5. The extent of excretion depends largely on the strain used for inoculation. With strains of apparently equal effectiveness in nitrogen fixation, the extent of excretion may vary considerably, so that actually such strains differ in their effectiveness.

Amino acid content of plants at different stages of growth.

INCREASING attention has lately been paid to the composition of the protein constituents of the green plants. Important work has been done in this field, particularly by Chibnall and Wright. In the present letter we wish to direct attention to an important but rather neglected question in the study of the plant proteins. One of us (A. I. V.) has already referred to this question in the discussion on the chemistry of grass crops at the recent Norwich meeting of the British Association1.

Excretion of Amino Acids from the Root Nodules of Leguminous Plants

AFTER having shown that amino acids appear in the medium in inoculated, but otherwise sterile, quartz sand cultures of leguminous plants, we assumed that these amino acids are excreted from the nodules. The experimental evidence then available did not, however, exclude the possibility that the excretion might be a function of the roots.