Seed Development
May 13, 2024 | by Bloom Code Studio
- Seed development generally consists of 3 stages: cell division and differentiation, accumulation of food reserve, maturation, and water loss.
- Seed development generally starts from fertilization which is preceded by pollination.
- In angiosperm, the ovule consists of two-layer the integument and nucellus. The nucellus cell undergoes meiosis and mitotic division to form eight nucleated embryo sacs. Pollen tube enters unto embryo sac and releases two gametes. One male gamete unites with the egg cell to form a diploid zygote that later develops into an embryo, while the other gamete unites with two polar nuclei to form a triploid endosperm that stores food for the growing embryo.
- The integuments of ovule change to seed coat with two distinct covering; outer testa and inner tegman.
- In some cases, there may be remnants of nucellar tissues called perisperm that stores food, but in most cases, it disappears.
- Endosperm nourishes the embryo by storing food material. In albuminous seed, endosperm remains conspicuous and a greater part of the seed than the embryo, while in other seeds like Tectona, the embryo uses all nutrition in development, and endosperm may disappear by the time of maturity. In such cases, the cotyledon is the organ for storage.
- Embryo development may vary that we may distinguish all the parts of embryo-like cotyledon, plumule, radicle, etc. In some angiosperms, more than one embryo may be developed in a single seed called polyembryony.
- In gymnosperm, there is a single integument that is fused with an ovuliferous scale consisting of paired ovules. At fertilization, the nucellus is separated from the integument only in the micropyle region. Meiosis and mitosis in nucellus take place the same as in angiosperm and form female gametophyte (multicellular, haploid) that grows further, replacing nucellus and differentiated into archegonia, each consisting of two large egg cells.
- One of the two gametes from the pollen tube is fertilized with the egg cell to form a zygote that later develops onto the embryo, while another one is either aborted (in Pinus) or may fertilize with other archegonia but never unite with polar nuclei to form endosperm.
- The mature seed consists of a seed coat developed from the integument, diploid perisperm developed from nucellus e.g., Pinus pinea, but in most cases, it disappears during development, and the haploid gametophyte tissue which nourishes the embryo, which is equivalent to the endosperm of angiosperm and the last one is embryo consists of plumule, radicle, cotyledon same as an angiosperm. Cotyledon number may vary in gymnosperm up to 18 (in pinus).
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