Endosperm

Source: Wikipedia, the free encyclopedia.
Wheat seed
Wheat seed

The endosperm is a tissue produced inside the

whole wheat flour), while barley endosperm is the main source of sugars for beer production. Other examples of endosperm that forms the bulk of the edible portion are coconut "meat" and coconut "water",[3] and corn. Some plants, such as orchids, lack endosperm in their seeds
.

Origin of endosperm

Ancestral flowering plants have seeds with small embryos and abundant endosperm. In some modern flowering plants, the Orchideae for example, the embryo occupies most of the seed and the endosperm is non-developed or consumed before the seed matures.[4][5] In other flowering plant taxa, the Poaceae for example, the endosperm is greatly developed.[6]

Double fertilization

Main article: Double fertilization

Endosperm is formed when the two

double fertilization
develops into the endosperm. Because it is formed by a separate fertilization, the endosperm constitutes an organism separate from the growing embryo.

About 70% of angiosperm species have endosperm cells that are

diploid (2n) to 15n.[8]

One flowering plant, Nuphar polysepala, has diploid endosperm, resulting from the fusion of a pollen nucleus with one, rather than two, maternal nuclei. The same is supposed for some other basal angiosperms.[9] It is believed that early in the development of angiosperm lineages, there was a duplication in this mode of reproduction, producing seven-celled/eight-nucleate female gametophytes, and triploid endosperms with a 2:1 maternal to paternal genome ratio.[10]

Double fertilisation is a characteristic feature of

angiosperms
.

Endosperm formation

There are three types of endosperm development:

Nuclear endosperm formation – where repeated free-nuclear divisions take place; if a cell wall is formed it will form after free-nuclear divisions. Commonly referred to as liquid endosperm. Coconut water is an example of this.

Cellular endosperm formation – where a cell-wall formation is coincident with nuclear divisions. Coconut meat is cellular endosperm. Acoraceae has cellular endosperm development while other monocots are helobial.

Helobial endosperm formation – where a cell wall is laid down between the first two nuclei, after which one half develops endosperm along the cellular pattern and the other half along the nuclear pattern.

Evolutionary origins

The evolutionary origins of double fertilization and endosperm are unclear, attracting researcher attention for over a century. There are the two major hypotheses:[8]

  • The double fertilization initially used to produce two identical, independent embryos ("twins"). Later these embryos acquired different roles, one growing into the mature organism, and another merely supporting it. Thus, the early endosperm was probably diploid, like the embryo. Some gymnosperms, such as Ephedra, may produce twin embryos by double fertilization. Either of these two embryos is capable of filling in the seed, but normally only one develops further (the other eventually aborts). Also, most basal angiosperms still contain the four-cell embryo sac and produce diploid endosperms.
  • Endosperm is the evolutionary remnant of the actual gametophyte, similar to the complex multicellular gametophytes found in gymnosperms. In this case, acquisition of the additional nucleus from the sperm cell is a later evolutionary step. This nucleus may provide the parental (not only maternal) organism with some control over endosperm development. Becoming triploid or polyploid are later evolutionary steps of this "primary gametophyte". Nonflowering seed plants (conifers, cycads, Ginkgo, Ephedra) form a large homozygous female gametophyte to nourish the embryo within a seed.[11]

The triploid transition - and the production of

antipodal cells - may have occurred due to a shift in gametophyte development which produced a new interaction with an auxin-dependent mechanism originating in the earliest angiosperms.[2]

The role of endosperm in seed development

In some groups (e.g. grains of the family

castor bean
, Ricinus communis) and others (including grains, such as wheat and corn) store mainly starches.

The dust-like seeds of

nucellus produces a nutritive tissue termed "perisperm". The endosperm of some species is responsible for seed dormancy.[13] Endosperm tissue also mediates the transfer of nutrients from the mother plant to the embryo, it acts as a location for gene imprinting, and is responsible for aborting seeds produced from genetically mismatched parents.[7] In angiosperms, the endosperm contain hormones such as cytokinins, which regulate cellular differentiation and embryonic organ formation.[14]

Cereal grains

Cereal crops are grown for their edible fruit (grains or caryopses), which are primarily endosperm. In the caryopsis, the thin fruit wall is fused to the seed coat. Therefore, the nutritious part of the grain is the seed and its endosperm. In some cases (e.g. wheat, rice) the endosperm is selectively retained in food processing (commonly called white flour), and the embryo (germ) and seed coat (bran) removed. The processed grain has a lower quality of nutrition. Endosperm thus has an important role within the human diet worldwide.

The aleurone is the outer layer of endosperm cells, present in all small grains and retained in many dicots with transient endosperm. The cereal aleurone functions for both storage and digestion. During germination, it secretes the amylase enzyme that breaks down endosperm starch into sugars to nourish the growing seedling.[15][16]

See also

References

  1. PMID 15306295
    .
  2. ^
    S2CID 206521265
    .
  3. ^ "Edible Palm Fruits". Wayne's Word: An Online Textbook of Natural History. Archived from the original on 2 September 2017. Retrieved 14 July 2010.
  4. ^ "The Seed Biology Place - Seed Dormancy". Seedbiology.de. Retrieved 2014-02-05.
  5. S2CID 19785565
  6. ^ academic.oup.com https://academic.oup.com/plphys/article/149/1/14/6107983. Retrieved 2024-03-05. {{cite web}}: Missing or empty |title= (help)
  7. ^
    ISBN 9783540712350
    .
  8. ^
    PMID 12225592
    .
  9. S2CID 4396197
    .
  10. S2CID 24303275
    .
  11. PMID 11607532
    .
  12. JSTOR 2436631
    .
  13. ISBN 978-0-8247-9192-6
    .
  14. ISBN 978-0-8493-2483-3
    .
  15. PMID 21109580
    .
  16. S2CID 5752973
    .

External links
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