Seed Coat Regulation of Soybean Seed Imbibition

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Abstract
Soybean [Glycine max (L.) Merr.] seeds are prone to imbibitional injury, which may culminate in significant economic losses. This study was designed to investigate the regulation of soybean seed imbibition by the seed coat. The intact seed coat delayed water uptake in the embryonic axis, cotyledons, and whole seed during the first 8 h soaking. The seed coat also assisted in tangential as well as radial displacement of water to the embryo. Scanning electron micrographs revealed a seed coat‐derived radicle pocket surrounding the radicle tip as well as hourglass cells in the seed coat, which decreased in size away from the hilum. The function of the radicle pocket and hour glass cells of the seed coat may be associated with water storage surrounding the embryonic axis. This is substantiated by the large water‐holding capacity of the seed coat compared to its fresh weight. Isolated seed coats absorbed 3.8 times their fresh weight in water. These studies ascribe a significant role to the seed coat in regulating embryo moisture uptake. Initially, the seed coat retards water uptake and/or governs the direction of water penetration to the embryo and eventually serves as a reservoir of water for the hydrating axis.