Haemoglobin and the oxygen uptake of leguminous root nodules

Abstract

It is shown that O2 enters the nodules of leguminous roots by diffusion in soln. across the wet cell walls. Values of the QO0 of whole nodules decrease with increasing size of nodule and are greater in O2 than in air. The Q02 of thin slices of nodules, of a thickness such that diffusion does not determine the rate of O2 uptake, is about 7-8 nl. kg. dry wt./ hr., while that for whole nodules is about 1-2 jul./mg. dry wt./hr. The Q02 values of whole and sliced ineffective nodules differed very little from those of whole and sliced effective nodules. Carbon monoxide in a concn. sufficient to convert practically all the nodule hemoglobin to carboxyhemoglobin had no effect on O2 uptake by detached effective nodules. An apparatus is described by means of which the O2 uptake of nodulated roots may be measured when these are attached to the plant. No effect of low concns. of carbon monoxide on the O2 uptake of attached nodules could be detected. The increase in 02 uptake brought about by addition of hemoglobin solns. to Rhizobium cells is shown to be unconnected with the ability of hemoglobin to undergo reversible oxygenation. Warburg''s observation that low concns. of carbon monoxide apparently stimulated O2 uptake by bird red blood cells was confirmed. This stimulation was temporary.