NITROGENASE ACTIVITY AND NITROGEN-FIXING BACTERIA ASSOCIATED WITH ROOT BASE AND ROOT-TIP OF RICE PLANTS

An assessment of nitrogenase activity associated with the basal and te rminal portions of rice roots from seven rice cultivars was made. Resu lts indicate a definite partitioning of the nitrogenase activity withi n the root and a plant growth dependent shift in the activity associat ed with basal and terminal portion of the roots. Nitrogenase activity associated with the root base steadily declined with plant growth, whi le root tip associated nitrogenase activity increased sharply. Further , the basal portion had higher nitrogenase activity in the prereproduc tive phase while the root tip had higher activity during reproductive and maturity stages of the plant. Microbiological analysis of plant ro ots indicated the association of higher populations of Azospirillum sp . and Azotobacter sp. with the root base, while the root tips had high er populations of facultative anaerobic nitrogen-fixing bacteria.