Nitrogen fixation in root nodules of Mucuna pruriens is reported but not well understood. In a nodule the arrangement of cells, the thickness of cortex, the metabolic activity of cells, the number of cells of a nodule involved in fixation, the photosynthate movement to the nodule, protein content and distribution of protein in a nodule as a measure of nitrogen fixation would determine the ability of nitrogen fixation of a genotype. The above parameters were studied in detail in 13 genotypes of Mucuna pruriens to understand the role of above parameters in nitrogen fixation using histochemical and histological techniques. The plants were grown at Indian Institute of Horticultural Research, Bangalore (13° 58¹ N 78° E) in a pot culture and nodules were collected at flowering stage of crop. The root nodules were fixed in Carnoy's B fluid. The nodules were processed and embedded in paraffin wax and thin sections were cut (8 μ m) and stained. Photosynthate movement within the nodule and supply to the nodule was assessed using Periodic acid Schiff's stain, metabolic activity of nodular cells were assessed using Toluidin blue stain, protein content was assessed using bromophenol blue stain. Results indicated that the genotype IIHR-MP-02 possessed higher number of cells per unit area in nodule, greater photosynthate movement to the nodule, higher concentration of protein in nodule and thicker cortex layer as the outer most nodule cover compared to all other genotypes probably making it highly efficient genotype in nitrogen fixation. These results help to understand why a particular genotype is efficient in nitrogen fixation over others.

Key words: histochemical, proteins, photosynthates, metabolic activity