Endosperm

The endosperm is a tissue that develops inside the seeds of most flowering plants after the seeds have been twice fertilised (fertilised twice). Most species are triploid (meaning they have three chromosomal sets per nucleus), which may be due to auxin stimulation. It forms a protective shell over the embryo and supplies nutrients in the form of starch, though it may also contain oils and proteins. Endosperm can be used as a source of nutrition in animal diets as a result of this. When it comes to bread making, wheat endosperm is used to make flour (the rest of the grain is also included in whole wheat flour), while barley endosperm is used to make beer, where it is the primary source of sugar for fermentation.

Double fertilisation

It is only after the two sperm nuclei contained within a pollen grain reach the interior of a female gametophyte that endosperm is created (sometimes called the embryo sac). During fertilisation, one sperm nucleus fertilises the egg cell, resulting in the formation of the zygote, while the other sperm nucleus normally fuses with the binucleate central cell, resulting in the formation of the primary endosperm cell (its nucleus is often called the triple fusion nucleus). The endosperm is formed from the cell that was generated during the process of double fertilisation. Because it is produced through a separate fertilisation process, the endosperm is considered to be a separate entity from the developing embryo.

Approximately 70% of angiosperm species have endosperm cells that are polyploid, according to the USDA. Although commonly triploid (having three sets of chromosomes), the number of chromosomes can range from two to fifteen in number.

The endosperm of one species of flowering plant, Nuphar polysepala, was shown to be diploid, resulting from the fusion of a pollen nucleus with one rather than two maternal nuclei. This is the first time that this has been demonstrated.

Endosperm formation

Endosperm development can be classified into three types:

• Cell wall formation occurs after repeated free-nuclear divisions in the case of nuclear endosperm formation, which occurs after repeated free-nuclear divisions in the case of a cell wall. It is also referred to as liquid endosperm in some circles. Coconut water is one example of this type of beverage.
• Cellular endosperm development occurs when the production of a cell wall occurs at the same time as nuclear divisions. Coconut meat is made up of cells called endosperm. The Acoraceae have cellular endosperm development, whereas other monocots have helobial endosperm development.
• When a cell wall is built down between the first two nuclei, the endosperm develops in two directions: one half grows endosperm along the cellular pattern and the other half develops endosperm along the nuclear pattern (helobial endosperm formation).

The role of endosperm in seed development

Endosperm is retained in some plant species until they reach the mature seed stage as a storage tissue (e.g., grains of the family Poaceae), while it is excreted in others (e.g., most members of the family Fabaceae, including the common bean, Phaseolus vulgaris), in which case the seeds are referred to as “exalbuminous” or “cotyledonous” and the storage tissue function is performed by enlarged cotyledons (“seed leaves”). It has been shown that the storage function of some species (e.g., maize, Zea mays) is distributed between both endosperm and embryo. Many plants, like castor beans and Ricinus communis, have mature endosperm tissue that contains primarily lipids, whereas others (including grains such as wheat and corn) have mature endosperm tissue that contains mostly carbohydrates.

Orchid seeds are dust-like in appearance and lack an endosperm. Early in their growth, orchid seedlings are mycoheterotrophic, meaning they feed on mycobacteria. It is also true that the endosperm does not develop in several other species, such as coffee. As a substitute, the nucellus generates a nutritive tissue known as “perisperm.” Some species’ seed dormancy is caused by the endosperm, which is found in their seeds. Aside from that, endosperm tissue is responsible for a number of other functions such as mediating the flow of nutrients from the mother plant to the embryo, serving as a site for gene imprinting, and aborting seeds generated by genetically mismatched parents.

Cereal grains

Grains and caryopses (edible fruits) of cereal crops are grown for their endosperm content, which is the primary component of the fruit. In the caryopsis, the thin fruit wall is bonded to the seed coat, resulting in a brittle fruit wall. As a result, the seed and its endosperm are the most nutritionally dense parts of the grain. During food processing, the endosperm (commonly known as white flour) is preferentially maintained while the embryo (germ) and seed coat (bran) are removed. This is done in some circumstances (for example, wheat and rice). The processed grain has a lesser nutritional quality than the unprocessed grain. As a result, endosperm plays a vital role in the human diet all throughout the world.

Conclusion

It is vital to note that the endosperm plays an important role in embryonic growth by delivering nutrients, safeguarding the embryo and limiting embryo growth by functioning as a mechanical barrier during seed development and germination, among other things. Plant species differ in their structure and function in the mature dry seed, with the structure and function being more specialised in some cases. A new understanding of the endosperm’s regulatory actions during seed germination has been gained through the investigation of its transcriptome. It is widely known that during germination, the embryo secretes signals to the endosperm that cause the deterioration of the seed reserve and the weakening of the endosperm to occur simultaneously. In recent years, breakthroughs in seed biology have demonstrated that the endosperm is capable of perceiving environmental cues, as well as of producing and secreting signals that regulate the development of the embryo. The process of embryo development and endosperm development is thus considered to be a systemic response including bidirectional interactions between the embryo and endosperm.