Hemoglobins in the nitrogen-fixing root nodules of actinorhizal plants

Abstract

The occurrence of high concentrations of hemoglobins in the root nodules of Casuarina cunninghamiana Miq. and Myrica gale L. has been confirmed using spectrophotometry of nodule segments. In an atmosphere of N2, absorption bands were observed at approximately 560 nm, while in O2, bands were found at 540 and 580 nm. These bands were rapidly reversed when O2 and N2 were interchanged in the gas phase. In the presence of CO, absorption bands at 540 and 570 nm were observed. Lower concentrations of hemoglobins were present in nodules of Comptonia peregrina (L.) Coult., Alnus rubra Bong., and Elaeagnus angustifolia L. Zero to trace amounts were found in Ceanothus americanus L. and Datisca glomerata (Presl.) Baill. Preparation of a crude extract from nodules of C. cunninghamiana indicated that the hemoglobin is in a soluble form. Other workers may have failed to observe hemoglobins in actinorhizal nodules because of the low concentrations in many nodules or because hemoglobin is restricted to the tissue containing the active endophyte, and this tissue occupies a relatively small fraction of the nodule volume.