Muhammad Asim, Muhammad Asif, Muhammad Munir* and Muhammad Aslam**
The uptake and distribution of abscisic acid (ABA) were studied in inoculated and uninoculated plants of soybean [Glycine max (L.) Merr.] from the time of inoculation to root-nodule initiation (192 hours after inoculation). 3H-ABA was applied to the leaves of two soybean cultivars: cv. Williams-82 and its hypernodulating mutant, NODI-3. There was a significant difference in the percent uptake of 3H-ABA between the two varieties both in inoculated and uninoculated plants. A marked difference in the percent distribution of 3H-ABA between different parts of the plants was observed at different developmental phases of root nodules. Leaves of NODI-3 retained more radioactivity as compared to Williams-82 in inoculated as well as uninoculated plants. The stem and roots of Williams-82 plants had a percent distribution of ABA that was higher than NODI-3. The phloem sap of Williams-82 had higher accumulation of 3H-ABA at all stages after treatment. The basal levels of ABA in phloem sap were lower in NODI- 3 than in Williams-82. Inoculation further accentuated this difference. The major changes in ABA level in phloem sap and leaves occurred between 48 to 96 h after inoculation.