RED, BROWN AND GREEN PIGMENTS IN LEGUMINOUS ROOT NODULES

Abstract

IN addition to the red pigment, hæmoglobin,· we have always found in leguminous root nodules a brown pigment. This is methæmoglobin with trivalent iron1. The simplest way of demonstrating its presence is to add sodium fluoride to the water extract of crushed nodules, whereby the characteristic absorption maximum of fluor-methæmoglobin at 610 mµ becomes visible. The equilibrium: hæmoglobin ⇄ methæmoglobin in the root nodules depends decisively on the intensity of light and on the stage of growth of the plants. The root nodules of vigorously growing legumes are red on bright days, the amount of hæmoglobin being high in comparison to that of methæmoglobin. During cloudy days the brown colour deepens in the nodules as the balance is shifted to methæmoglobin. If soybean is kept in complete darkness for two to three days, the colour of the nodules changes to brown. After a longer stay in the dark the colour turns green. In the pea the green colour is formed in a noticeably shorter time than in soybean².