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

Abstract

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. Bond's 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.

Excretion of nitrogen by leguminous plants

“…In Exp. I the evidence for excretion is clear-cut, especially with the Finnish culture HZ; culture PP had previously been found to excrete less than did HZ (Virtanen et al 1937). Although the total quantity of nitrogen fixed by the peas was rather small, the relative amount excreted compares quite favourably with that previously reported by Virtanen and associates (1937).…”

“…At his invitation one of us (P. W. W.) 1 visited his Institute in Helsinki and carried out experiments with a pea-barley mixture using both the "sterile"and non-sterile techniques (Virtanen, 1935;Virtanenet al 1937). The details of the methods employed have been recently summarized by Virtanen et al (1937). In the Wisconsin experiments only the non-sterile, i.e.…”

“…at Wisconsin, while wet sand was sterilized for only 4 hr. at Helsinki; sodium hypochlorite was employed for sterilization of seed at Wisconsin (Hopkins et al 1931); HgCl 2 was used at Helsinki (Virtanen et al 1937).…”

“…The aseptic transfer of the seedlings of barley and pea for the " sterile " technique (Virtanen et al 1937) was made in the transfer chamber previously described (Hopkins et al 1931). In general, these experiments included some which were exact duplicates of those made in Helsinki except that American types of sand were used and the general environment, e.g.…”

“…greenhouse and weather, were necessarily different. Virtanen et al (1937) have recently published accounts concerning the importance of the adsorptive properties of the substrate employed for securing excretion. It is of interest to compare the physical properties of the sands used with those of the Finnish sand.…”