Seed germination implies an expansion process restarting the growth of the embryonic axis (Ax) and which is completed by radicle emergence through the seed covering layers. In developing soybean seeds, abscisic acid in Ax (ABAa) mainly inhibits Ax growth. Additionally, the expression of the EXP1 gene at the elongation zone (EZ) was found to be involved in the promotion of mature soybean Ax growth, which increased during water incubation and which was repressed by exogenous ABA. This work aimed to evaluate (1) the ABAa and EXP1 levels at the EZ and (2) the role of the seed coat (SC) in developing soybean seed germination. Whole seeds (Se), embryos (Em) and Ax at 25–45 d after anthesis (DAA) germinated in vitro, and germination performance increased with DAA. ABAa decreased in planta from 25 DAA until its critical non-inhibitory threshold (ABAc) at around physiological maturity (45 DAA). At earlier ages, the ABAc was reached during the in vitro incubation. Concomitantly, EXP1 transcripts accumulated with age into the pool of long-lived mRNAs and were up-regulated during incubation. Additionally, isolated Ax germinated faster, took up more water and increased its water potential more rapidly during incubation than Ax in Se. Also, a lower osmotic gradient was required to germinate at 45 DAA, when ABAa was no longer inhibitory. Simultaneously, the pressure to protrude SC through the micropylar area increased from 25 to 45 DAA. These results support the role of ABAa and EXP1 in controlling Ax growth and the SC in delaying radicle protrusion.

种子萌发意味着重新开始胚轴 (Ax) 生长的扩展过程，该过程由胚根通过种子覆盖层出现而完成。在大豆种子发育过程中，Ax 中的脱落酸 (ABAa) 主要抑制 Ax 生长。此外，发现延伸区 (EZ) 的EXP1基因的表达与促进成熟大豆 Ax 生长有关，这种生长在水培养过程中增加，并被外源 ABA 抑制。这项工作旨在评估 (1) EZ 的 ABAa 和EXP1水平和 (2) 种皮 (SC) 在发育大豆种子萌发中的作用。花后 25-45 d 的整粒种子 (Se)、胚胎 (Em) 和 Ax (DAA)在体外萌发, 并且发芽性能随着 DAA 的增加而增加。ABAa在植物中从 25 DAA 下降，直到其在生理成熟（45 DAA）左右的临界非抑制阈值（ABAc）。在较早的年龄，ABAc在体外孵化期间达到。同时，EXP1随着年龄的增长，转录物积累到长寿命的 mRNA 池中，并在孵化过程中被上调。此外，在孵化过程中，分离的 Ax 比 Se 中的 Ax 发芽更快、吸收更多的水并更快地增加其水势。此外，当 ABAa 不再具有抑制作用时，需要较低的渗透梯度才能在 45 DAA 萌发。同时，通过珠孔区域突出 SC 的压力从 25 DAA 增加到 45 DAA。这些结果支持 ABAa 和EXP1在控制 Ax 生长和 SC 在延迟胚根突出中的作用。