Comparative study of N uptake and distribution in three lines of common bean (Phaseolus vulgaris L.) at early pod filling stage

Summary

The uptake and distribution of¹⁵NH ⁺₄ ,¹⁵NO ⁻₃ and¹⁵N₂ was studied in greenhouse-grown beans (Phaseolus vulgaris L.) with a commercial cultivar and 2 recombinant inbred backcross lines;¹⁵N was supplied in the nutrient solution at the R3 (50% bloom) stage. Plants were harvested 1, 5 and 10 days after treatment, and were separated into nodules, roots, stems, mature leaflets, immature leaflets, and flowers/fruits. All 3 lines showed rapid increases in the N content of flowers/fruits after the R3 stage. However, the percentage N in these tissues decreased after the R3 stage.

One of the recombinant lines showed a greater uptake of NH ⁺₄ than the other 2 lines. Rates of¹⁵N₂ fixation and NO ⁻₃ uptake were similar for all 3 lines, N₂ fixation estimated from total N content showed the 2 recombinant lines with 24 and 34 percent greater activity than the commercial cultivar.

Distribution of¹⁵N at the whole plant level was similar for all 3 lines for a similar N source.¹⁵NO ⁻₃ was transported first to leaflets and the label then moved into flowers/fruits. Transport of fixed N₂ was from the nodules to roots, stems and into flowers/fruits; usually less than 10 percent entered the leaflets. This indicates that N₂ fixation furnishes N directly to flowers/fruits with over 50 percent of the fixed N being deposited into flowers/fruits within 5 days after treatment.