Partitioning of Soybean Seed Composition Constituents as Affected by Node Position and Cultivar Differences.

Differences in seed composition constituents along the main stem in soybean are not well understood. Therefore, the objective of this study was to investigate the partitioning of  seed protein, oil, and fatty acids in seed along the main stem nodes in four soybean cultivars. The cultivars were DT 97-4290, maturity group (MG) IV, indeterminate; Stressland, MG IV, indeterminate; Hutcheson, MG V, determinate; TracyM, MG VI, determinate. Seed was harvested based on position on the plant (top nodes, middle nodes, and bottom nodes).  At R8, DT97-4290, Hutcheson, and Stressland had a higher percentage of protein and oleic acid and a lower percentage of oil and linolenic acid in top node seed compared with bottom node seed. The increase of protein in top node compared with the bottom node seed across the two experiments ranged from 15.5-19.5%, 7.0-10.5%, 14.2-15.8%, 11.2-16.5%, respectively for DT97-4290, Hutcheson, Stressland, and TracyM. Except for TracyM, the increase of oleic acid in the top node ranged from 45.4 to 93%, depending on the cultivar. Conversely, the decrease in the top node seed ranged from 14.4 to 26.8% for oil and from 5.7 to 34.4% for linolenic acid, depending on the cultivar. The higher protein and oleic acid concentrations in the top node seed was accompanied by higher activity of nitrate reductase activity (µmol nitrite g fwt^-1 hour^-1), higher chlorophyll concentration (g gfwt^-1), higher nitrogen (N) and sulfur (S) percentages in the fully expanded leaves at R5-R6, and higher seed nitrogen (N) and sulfur (S) percentages in DT 97-4290 and Stressland. The results suggest that the partitioning of seed protein, oil, and fatty acids in nodes along the plant depended on node position on the main stem, cultivar/genotype differences, seed N and S status, and tissue N and S partitioning. This information is useful for germplasm evaluation of soybean breeding lines, especially for single plant selection.