Determination of leghemoglobin components and xylem sap composition by capillary electrophoresis in hypernodulation soybean mutants cultivated in thefield

The hypernodulation soybean mutant lines (NOD1-3, NOD2-4, NOD3-7) and their parent Williams, and the mutant En6500 and its parent Enrei were cultivate d in a sandy dune field in Niigata, and the nodules and root bleeding xylem sap were sampled at 50, 70, 90, and 120 d after planting (DAP). The nodule size distribution patterns and concentration of leghemoglobin components w ere determined. The number of nodules of the hypernodulation mutant lines w as about two to three times higher than that of the parent lines irrespecti ve of the sampling date. At 50 DAP the nodule size was relatively smaller i n the hypernodulation mutant lines, and the total dry weight of the nodules was almost the same in the mutant lines and their parents. At 70 DAP and 9 0 DAP, the size distribution of the hypernodulation mutant nodules became a lmost the same as that of the parent lines, and both the number and total d ry weight of the nodules were higher than those of the parent lines. The co ncentration of four Lb components was separately measured by capillary elec trophoresis. The concentration of the Lb components in the hypernodulation mutant lines tended to be lower than in the parents, but the component rati os were not different between the hypernodulation mutants and their parents . Under field conditions, plant growth and nodulation characteristics were more similar between mutants and parents than in the hydroponic culture rep orted previously, although the mutants did exhibit hypernodulation traits. These findings suggest that the decrease in the Lb concentration and the di fferent Lb components ratios in the mutants may be caused by secondary effe cts of excess nodulation, such as photosynthate deficiency, rather than by a genetic defect in mutation. The concentration of major nitrogenous compou nds (allantoic acid, allantoin, asparagine, aspartic acid, and nitrate) in the xylem sap was also measured by capillary electrophoresis. The concentra tion of ureides and nitrate in xylem sap decreased with the plant age, but the asparagine concentration increased during the same period. The concentr ations of ureides and asparagine were higher, and the nitrate concentration was lower in the mutant lines than in their parents, possibly due to the h igher dependence on N-2 fixation than NO3- utilization. In the xylem sap, n itrate was the major inorganic anion followed by phosphate, sulfate, and ch loride, and potassium was the major cation followed by calcium or magnesium and sodium.