Allocation of photosynthetic products in soybean during the early stages of nodule formation

A time-course study examining the current photosynthate allocation of soybean (Glycine max [L.] Merr.) cv. Williams was conducted in relation to nodule initiation. Whole shoots were exposed to 14CO2 for 120 min and the distribution of radioactivity in each organ was determined. During the early stages of nodule formation (i.e. 4, 6 and 8 days after inoculation) the 14C distribution to the inoculated roots did not increase when compared with uninoculated control roots. In addition, the 14C respired by underground parts was similar in both the inoculated and the control roots. Eight days after inoculation, the accumulation of starch and sugar was similar in both inoculated and uninoculated plants. These results indicate that photosynthate allocation for nodule initiation does not increase markedly during the early stages of nodule formation. After the emergence of the nodules, photosynthate allocation to the inoculated roots gradually increased. In addition, the consumption of current photosynthate by the respiration of underground parts increased at day 12 after inoculation, but did not increase at day 8 after inoculation.