Study of seed coat microsculpture organization during seed development in iZygophyllum fabago/i (Zygophyllaceae)

摘要

The ontogeny of seed coat and endosperm tissue in Zygophyllum fabago L. was studied to determine their developmental importance using different histochemical and microscopic techniques. Our results revealed that the ovuleof Z. fabago was of the anatropous and bitegmic type. The inner epidermis cells were retained up to the end of seed development, whereas the other layers were removed in the early stages. Moreover, the outer integument was changed into the seed coat sculptures during the seed development. Concurrently, multiple cytoplasmic strings were formed at the seed coat cells. Fluorescence microscopic analysis indicated that callose and polyphenols were laid down at these strings. In the late stages of the seed development, the nucleus and cytoplasm of the cells were degenerated and the sculptures became obvious on the seed coat. The seed coat sculptures may play a role in the seed dispersal by wind. During the early developmental stages, the endosperm was of the nuclear type and then changed into the cellular type. Cytochemical tests indicated that in the later stages of seed development, the formation of starch grains and the thickening of cell walls occurred, causing considerable reduction of cell cavities as well as hardening the tissue. The cell storage in the endosperm tissue was more lipid-based than protein-based. Generally, due to the degeneration of the outer integument and the existence of the thin inner integument, the endosperm cell wall seemed to be thickened to protect the embryo and to save carbohydrates. The obtained results shed more light on the development of seed tissues in the family Zygophillaceae.