Seed desiccation during maturation is important for seed post-maturation behavior and harvest. However, the desiccation mechanism in soybean [Glycine max (L.) Merr.] seed maturation is hardly known. In this study, we found that water content in seeds, pods, and pedicels decreased faster than that in peduncles and stems. Therefore, we focused on the role of the pedicel during seed maturation. Morphological analysis revealed deposits in xylem vessels in the pedicel at 61 d after flowering (DAF), but no deposits in the peduncle. Microarray analysis showed that lignin biosynthesis-related genes were expressed in the pedicel at 61 DAF. Among them, the expression of GmPAL, Gm4CL, GmC3H, and GmCAD increased in the pedicel during seed maturation. Pedicel lignin content also increased by 61 DAF; lignin accumulated in xylem vessels. These results suggest that lignin deposits in pedicel xylem vessels cause soybean seed desiccation during maturation.
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