Seed coat anatomy of Cercis chinensis and its relationship to water uptake

Abstract

The hard seed coat of Cercis chinensis Bunge is an important factor of its dormancy. A study of the characteristics of water absorption is vital for understanding seed dormancy and germination. This investigation found that soaking in water at an initial temperature of 80 °C for 5 min was optimal for breaking the hardness of C. chinensis seeds. Scanning electron microscopy (SEM), dye-tracking, and blocking experiments were used to examine the major water entry sites and the relationship between water uptake and seed coat structure during C. chinensis seed imbibition. The SEM images showed that the seed coat consisted of three layers: epidermis, palisade, and sclereid. Special light line, vascular bundle, and counter-palisade layer structures were found in the side of the hilum. The blocking experiments showed that the hilar region was an important water absorption site because, if the region was not blocked, it showed the highest water absorption when imbibed for 3–12 h. However, all parts of the seed coat can absorb water if enough time is allowed after the seed coat hardness has been broken. The dye-tracking test showed that after 3 h water entered the seed only via the hilum fissure. Therefore, the hilum fissure acts as the initial site of water absorption. When more time was allowed, water moved more rapidly on the side with vascular bundles than on the opposite side.