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Abstract: Nitrate reductase (NR) activity in the flag leaf blade, flag leaf sheath and the shoots below first leaf blade of three cultivars of bean seeds (Lablab purureus L.) limiting the N assimilation was investigated during the grain filling (post anthesis) period. After anthesis NR activities in the flag leaf blade, flag leaf sheath and the shoots below first leaf blade in vitro assayed twice in a week. Activity declined during the period in apparent associating with the senescence of tissues. In contrast, when NR estimates were made by a modified assay in which no exogenous nitrate was supplied, activity was consistently low. This suggested that relatively little nitrate was available for reduction in these tissues although NR enzyme appeared to be there. The cultivars accumulated approximately 85% of their total reduced N before anthesis. Nitrogen accumulation, when nitrate was induced was substantially greater than the accumulation actually observed. So the results suggested that the minimal accumulation of reductase N after anthesis by the cultivars in this study should not be attributed to the level of NR enzyme. It might be more a function of a limitation in a process responsible for supplying nitrate to the enzyme.