The endosperms, which is the plant's food supply. It surrounds the growing embryo and provides food for it.
The endosperm is a tissue produced inside the seeds of most of the flowering plants following fertilization. It surrounds the embryo and provides nutrition in the form of starch, though it can also contain oils and protein. This can make endosperm a source of nutrition in animal diet. For example, wheat endosperm is ground into flour for bread (the rest of the grain is included as well in 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",[1] 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, 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.[2][3]
Double fertilization
Endosperm is formed when the two sperm nuclei inside a pollen grain reach the interior of a female gametophyte (sometimes called the 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 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.[4] These are typically triploid (containing three sets of chromosomes), but can vary widely from diploid (2n) to 15n.[5]
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.[6] 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.[7]
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.