Phosphatase activity and phosphorus partitioning in nodules of developing mungbean

The acid and alkaline phosphatase activities were determined in bacteroid free fraction of nodules during development, using different phosphorylated substrates. Both enzymes change their substrate specificities with nodule development. Alkaline phosphatase, 20 days after sowing (DAS), showed negligible activity with ATP while at later stages maximum activity with ATP was observed. Invariably fructose 1,6 bisphosphate was a better substrate compared to fructose-6-phosphate and glucose-6-phosphate. Using Sephadex G-150 column chromatography, only one peak of acid phosphatase around Ve/Vo of 2.2 to 2.3 was observed at 20 and 30 DAS stages while at 40 DAS stage an additional ATP specific peak at around Ve/Vo of 2.9 was also observed. There was only one alkaline phosphatase peak at 20 and 30 DAS. However, at 40 DAS additional ATP specific peaks of phosphatases were observed at Ve/Vo of 1.4 and 2.6. Alkaline phosphatase could not be detected in the bacteroids whereas activity of acid phosphatase was about 5–7 % of that observed in the bacteroid free preparation. A low activity of both acid and alkaline phytases was observed at all stages of nodule development. However, phytic acid could not be detected. Increase in phosphorus content of water soluble organic phosphate at late stage of nodule development appears to be related with low level of phosphatase activity.