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350px, right The endosperm is a tissue produced inside the seeds of most of the
flowering plant The flowering plants, also known as Angiospermae (), or Magnoliophyta (), are the most diverse group of Embryophyte, land plants, with 64 Order(biology), orders, 416 Family (biology), families, approximately 13,000 known Genus, genera and 300,000 ...
s following fertilization. It is triploid (meaning three chromosome sets per nucleus) in most species. It surrounds the
embryo An embryo is the early stage of development of a multicellular organism. In general, in organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodi ...
and provides nutrition in the form of
starch Starch or amylum is a polymeric carbohydrate consisting of numerous glucose Glucose is a simple sugar with the Chemical formula#Molecular formula, molecular formula . Glucose is the most abundant monosaccharide, a subcategory of carbohydrates ...
, though it can also contain oils and
protein Proteins are large biomolecules or macromolecules that are comprised of one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing m ...
. This can make endosperm a source of nutrition in animal diet. For example,
wheat Wheat is a grass widely Agriculture, cultivated for its seed, a cereal grain which is a worldwide staple food. The Taxonomy of wheat, many species of wheat together make up the genus ''Triticum''; the most widely grown is common wheat (''T. aest ...

wheat
endosperm is ground into flour for
bread Bread is a staple food prepared from a dough of flour and water Water is an Inorganic compound, inorganic, Transparency and translucency, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, wh ...
(the rest of the grain is included as well in whole wheat flour), while
barley Barley (''Hordeum vulgare''), a member of the grass family, is a major cereal grain grown in temperate climates globally. It was one of the first cultivated grains, particularly in Eurasia Eurasia () is the largest continental area on E ...

barley
endosperm is the main source of sugars for
beer Beer is one of the oldest and most widely consumed alcoholic drink An alcoholic drink is a drink that contains ethanol Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic chemical ...
production. Other examples of endosperm that forms the bulk of the edible portion are
coconut
coconut
"meat" and coconut "water", and
corn Maize ( ; ''Zea mays'' subsp. ''mays'', from es, maíz after tnq, mahiz), also known as corn (North American North America is a continent entirely within the Northern Hemisphere and almost all within the Western Hemisphere. It can ...
. Some plants, such as
orchid
orchid
s, lack endosperm in their seeds.


Origin of endosperm

Ancestral flowering plants have seeds with small embryos and abundant endosperm, and the evolutionary development of flowering plants tends to show a trend towards plants with mature seeds with little or no endosperm. In more derived flowering plants the embryo occupies most of the seed and the endosperm is non-developed or consumed before the seed matures.


Endosperm is formed when the two
sperm Sperm is the male reproductive Cell (biology), cell, or gamete, in anisogamous forms of sexual reproduction (forms in which there is a larger, "female" reproductive cell and a smaller, "male" one). Animals produce motile sperm with a tail known ...
nuclei inside a
pollen Pollen Tube Diagram Pollen is a powdery substance consisting of pollen grains which are male microgametophytes of seed plants, which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects the ...
grain reach the interior of a female gametophyte (sometimes called the ovule, embryo sac). One sperm nucleus fertilizes the egg cell, forming a zygote, while the other sperm nucleus usually fuses with the binucleate central cell, forming a primary endosperm cell (its nucleus is often called the ''triple fusion nucleus''). That cell created in the process of double fertilisation, 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 polyploid. These are typically triploid (containing three sets of Chromosome, chromosomes), but can vary widely from diploid (2n) to 15n. One species of flowering plant, ''Nuphar polysepala'', has been shown to have endosperm that is diploid, resulting from the fusion of a pollen nucleus with one, rather than two, maternal nuclei. The same is supposed for some other basal angiosperms. 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. Double fertilisation is a characteristic feature of angiosperms. It is used in many Biotechnology, biotechnological processes


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, 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: * 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 (plant), 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.


The role of endosperm in seed development

In some groups (e.g. grains of the family Poaceae) the endosperm persists to the mature seed stage as a storage tissue, in which case the seeds are called "albuminous" or "endospermous", and in others it is absorbed during embryo development (e.g., most members of the family Fabaceae, including the common bean, ''Phaseolus vulgaris''), in which case the seeds are called "exalbuminous" or "cotyledonous" and the function of storage tissue is performed by enlarged cotyledons ("seed leaves"). In certain species (e.g. corn, ''Zea mays''); the storage function is distributed between both endosperm and the embryo. Some mature endosperm tissue stores fats (e.g. castor bean, ''Ricinus communis'') and others (including grains, such as wheat and corn) store mainly starches. The dust-like seeds of s have no endosperm. Orchid seedlings are mycoheterotrophy, mycoheterotrophic in their early development. In some other species, such as coffee, the endosperm also does not develop. Instead, the nucellus produces a nutritive tissue termed "perisperm". The endosperm of some species is responsible for seed dormancy. 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. In angiosperms, the endosperm contain hormones such as cytokinins, which regulate cellular differentiation and embryonic organ formation.


Cereal grains

Cereal crops are grown for their edible fruit (grains or caryopsis, 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 Flour, white flour), and the embryo (Cereal germ, 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.


See also

* Ovule


References


External links

*
Endosperm: the pivot of the sexual conflict in flowering plants
at Earthling Nature {{Authority control Plant morphology Plant physiology