Soybean Seed Phenol, Lignin, and Isoflavones Partitioning as Affected by Seed Node Position and Genotype Differences

Abstract

Factors controlling the production and partitioning of seed phenolics within soybean are not understood. Understanding these factors may justify selection for higher levels of seed phenolics because of their beneficial impact on human health and soybean defense mechanism against diseases. The objective of this research was to investigate the partitioning of seed phenolics (phenol, lignin, and isoflavones) along the main stem of soybean genotypes. A repeated greenhouse experiment was conducted on different soybean genotypes of different maturity and different stem architecture (determinate and indeterminate). Genotypes were DT 97-4290, maturity group (MG) IV; Stressland, MG IV; Hutcheson, MG V; and Tracy-M, MG VI. Seed were harvested from top and bottom nodes at seed-fill stage (R6) and harvest maturity stage (R8). At R6, seed phenolic compounds (phenol, lignin, and isoflavones daidzein, genistein, and glycitein) were greater in the bottom seed than the top seed. This trend was observed in DT 97-4290, Tracy-M, and Hutcheson, but not in Stressland. Also, this trend was more obvious with daidzein and genistein isoflavones than glycitein. The maximum phenolic compounds were recorded at R8. The higher phenolic compounds concentration in bottom seed than in top seed was accompanied by higher cell wall boron (B) percentage and lower total B in bottom seed. The current research demonstrated that phenolic compounds partitioned differently between the top and bottom seed nodes. This trend cannot be generalized in soybean genotypes unless enough germplasm is tested. The partitioning of higher pheno-lic compounds concentration along the main stem would allow for single seed selection in the breeding program for higher levels of phenolic compounds and for accurate measurements of seed phenolics in breeding lines. The association of B trend with phenolic compound trend may suggest B involvement in phenolic metabolism, and support the structural role of B. Breeding for higher levels of phenolics, especially isoflavones, would benefit human health, provide higher nutritional value of soy meal, and increase plant disease resistance.