LAUSR

• Water uptake is the fundamental and essential requirement for seed germination. Pecan seed has a hard woody endocarp and plays an important role during water uptake. • To explore the laws of water uptake during germination, the spatiotemporal pattern of water and the effect of endocarp were analysed by water measuring, high-field magnetic resonance imaging (MRI), dye-tracing, blocking and scanning electron microscopy (SEM). • Isolated seeds finish water uptake in 8h while whole seeds take 6d, and the cracking of endocarp plays an important role. The hilum is the channel for water to enter the seed, the rest of the seed coat consist of cells covered with a waxy layer and act as a barrier that made it difficult to absorb water. The region with the highest water contents in pecan seed was the edge of the U-shaped region and the water progressively diffused from the edge of the U-shaped region to the whole kernel. • There seems to be a new water absorption stage between phase II and phase III of triphasic model of water uptake of pecan seeds. The cracking of endocarp changed the water distribution in pecan seeds, which may be the trigger for further water absorption and radicle elongation.