Nature of the Excretion of Nitrogen Compounds from Legume Nodules

Abstract

FURTHER to our earlier communications concerning the excretion of nitrogen compounds from the nodules of leguminous species, I wish to add the following: a distinct excretion occurs only in media capable of absorbing the excreted amino acids. In water cultures, whether plain or filled with glass beads, the excretion is quite negligible. Addition of cellulose to the liquid medium results in a clearly detectable excretion. A much more powerful excretion occurs, however, in media consisting of kaolin, sand or soil. These materials absorb the excreted amino acids to such an extent that their extraction from the medium with water is very tedious and difficult. On the basis of these observations, it seems that the distribution of the nitrogen compounds between the nodule and the external medium is determined by an equilibrium. The presence of absorbing materials shifts this equilibrium to the side of the medium, and causes the excretion to occur. On the other hand, the host plant also takes up nitrogenous matter from the nodules. The equilibrium is therefore a very com-plicated one, and the rate of excretion depends largely on the ability of the host plant to utilize the nitrogen compounds fixed and synthesized in the nodules. Our observation that the rate of excretion is the higher, the greater the quantity of sand, is in accordance with this view. We have shown earlier¹ that the air content of the medium influences largely the function of the nodule, although it apparently has no specific effect on excretion, as we assumed earlier.