Water absorption characteristics and ecological adaptability of Iris hexagona seeds

Iris hexagona Walter can grow both in fresh water and salt water. Using basic morphological observation, dye-tracking test, and nuclear magnetic resonance (NMR) techniques, we observed the water absorption process of seed, compared the difference in seed water absorption, so as to understand the water absorption characteristics of the seeds grown in different water environments. Blocking and dye-tracking tests showed that the exotesta of seed exhibited strong permeability, especially the region around hilum was the heaviest to water absorption. Further research by NMR indicated that the micropyle was also an important channel for water to enter. After soaking for 0–2 h, it was the rapid water absorption stage (stage I), and then entered hysteresis stage (stage II). In particular, free water content in endosperm and embryo increased as the bound water content decreased during the seed imbibition. Compared with those in fresh water, the water absorption efficiency of the seed in salt solution decreased in the early stage, but the final water absorption efficiency was not significantly different from that of the fresh water. In short, I. hexagona seeds do not have water absorption barriers, and the water absorption efficiency of seed is not affected by the external salt environment. Water absorption from the exotesta could increase seed weight rapidly to help the seed sink into mire, while water absorption in the micropyle could activate the embryo and endosperm to be aid of seed germination.