Effect of Nitrate on Components of Nodule Leghaemoglobins

Abstract

Multiple components of leghaemoglobins (Lbs) from several legume species have been separated by polyacrylamide gel electrophoresis (PAGE), and identified by densitometry at 405 nm, extraction from gels and formation of their respective CO-ferrous complexes. Components were numbered consecutively starting from the anode side, and their relative concentrations were calculated by densitometry in control and $NO3-$ -treated nodules. The number of Lb components was five in Pisum sativum, four in Glycine max, at least two in Lupinus luteus and Trifolium repens, and two in Vigna radiata and V. unguiculata. Only one component was detected in fresh nodules of Phaseolus vulgaris. Nitrate significantly reduced the total content of Lb in all legumes, except Lupinus, the extent of reduction varying with the species. It also had a major effect on the proportions of components, causing an inversion in the relative abundance of Lb I and Lb II of V. radiata: the concentration of Lb I increased from 8% to 81% with $NO3-$ application, while total Lb only decreased by 13%. Drastic changes in proportions of Lb components were not artifactual and cannot be attributed exclusively to different turnover rates. They should correspond to variations in biosynthesis of the various components, probably originating at the genetic level.