Ovule

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Ovule

"Micropyle" redirects here. For the structure in animals, see Micropyle (zoology).

Ovule literally means "small egg

Ovum

An ovum is a haploid female reproductive cell or gamete. Both animals and embryophytes have ova. The term ovule is used for the young ovum of an animal, as well as the plant structure that carries the female gametophyte and egg cell and develops into a seed after fertilization....
." In seed plants, the ovule is the structure that gives rise to and contains the female reproductive cells. It consists of three parts: The integuments forming its outer layer, the nucellus (or megasporangium

Sporangium

A sporangium is a plant or fungus structure producing and containing spores. Sporangia occur in Flowering plant, gymnosperms, ferns, fern allies, bryophytes, Algaee, and Fungus....
), and the megaspore-derived female gametophyte (or megagametophyte) in its center.

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Encyclopedia

"Micropyle" redirects here. For the structure in animals, see Micropyle (zoology).

Ovule literally means "small egg

Ovum

Sporangium

Ovum

An ovum is a haploid female reproductive cell or gamete. Both animals and embryophytes have ova. The term ovule is used for the young ovum of an animal, as well as the plant structure that carries the female gametophyte and egg cell and develops into a seed after fertilization....
for fertilization. After fertilization, the ovule develops into a seed

Seed

A seed is a small Plant embryogenesis plant enclosed in a covering called the seed coat, usually with some Food storage. It is the product of the ripened ovule of gymnosperm and angiosperm plants which occurs after fertilization and some growth within the mother plant....
.

Location within the plant

In flowering plants, the ovule is located within the actual flower

Flower

A flower, sometimes known as a bloom or blossom, is the reproduction structure found in flowering plants . The biological function of a flower is to mediate the union of male sperm with female ovum in order to produce seeds....
, the part of the carpel known as the ovary

Ovary (plants)

In the flowering plants, an ovary is a part of the female reproductive organ of the flower or gynoecium. Specifically, it is the part of the carpel which holds the ovule and is located above or below or at the point of connection with the base of the petals and sepals....
, which ultimately becomes the fruit

Fruit

The term fruit has different meanings dependent on context, and the term is not synonymous in food preparation and biology. In botany, which is the scientific study of plants, fruits are the ripened Ovary of flowering plants....
. Depending on the plant, flowers may have one or multiple ovules per ovary. The ovule is attached to the placental wall of the ovary through a structure known as the funiculus

Funiculus

The cerebrospinal nerves consist of numerous nerve fibers collected together and enclosed in membranous sheaths. A small bundle of fibers, enclosed in a tubular sheath, is called a funiculus; if the nerve is of small size, it may consist only of a single funiculus; but if large, the funiculi are collected together into larger bundles or fasci...
, the plant equivalent of an umbilical cord

Umbilical cord

In placental mammals, the umbilical cord is the connecting cord from the developing embryo or fetus to the placenta. During prenatal development, the umbilical cord comes from the same zygote as the fetus and normally contains two arteries and one vein , buried within Wharton's jelly....
. Different patterns of ovule attachment, or placentation

Placentation

In biology, placentation refers to the formation, type and structure, or arrangement of placentas. The function of placentation is to transfers nutrients from maternal tissue to a growing embryo....
, can be found among plants: In parietal placentation, the ovules are attached to the outer ovary wall, whereas in free central placentation, they are attached to a central column within the ovary. In axile placentation, they are attached to radial spokes within the ovary.

In gymnosperm

Gymnosperm

Gymnosperm is a group of spermatophyte seed-bearing plants with ovules on scales, which are usually arranged in cone-like structures. The other major group of seed-bearing plants, the angiosperms, [from the Greek, 'angion' - container] have ovules enclosed in a carpel, a sporophyll with fused margins....
s such as conifers and similar plants, the ovules are borne unenclosed on the surface of an ovuliferous (ovule-bearing) scale, usually within an ovulate cone

Conifer cone

A cone is an organ on plants in the division Pinophyta that contains the plant sexuality structures. The familiar woody cone is the female cone, which produces seeds....
(also called megastrobilus

Strobilus

A strobilus is an organ of many plants that contains the reproductive structures. Strobili are ordinarily called cones in many of these groups....
).

Ovule parts and development

The ovule is composed of diploid maternal tissue that gives rise to the haploid tissue of the female gametophyte. The maternal tissues of the ovule include the integuments and the nucellus. The next "generation" formed within the ovule are the haploid megaspore and megagametophyte, or embryo sac. After fertilization of the egg cell and formation of a zygote

Zygote

A zygote is a cell that is the result of fertilization. That is, two ploidy cells—usually an ovum from a female and a sperm cell from a male—merge into a single ploidy cell called the zygote ....
, the ovule contains the embryo

Embryo

An embryo is a multicellular organism ploidy eukaryote in its earliest stage of development, from the time of first cell division until birth, Egg , or germination....
of the next sporophyte

Sporophyte

All land plants, and some algae, have life cycles in which a haploid gametophyte generation alternates with a diploid sporophyte, the generation of a plant or alga that has a double set of chromosomes....
generation and, in flowering plants, the triploid endosperm

Endosperm

Endosperm is the tissue produced in the seeds of most flowering plants around the time of fertilization. It surrounds the embryo and provides nutrition in the form of starch, though it can also contain Vegetable oils and protein....
.

Integuments, micropyle and chalaza

The integuments are the outer cell layers of the ovule enclosing the nucellus. Gymnosperms typically have one integument layer while angiosperms typically have two. The integuments develop into the seed coat when the ovule matures after fertilization.

The integuments do not enclose the nucellus completely but leave an opening at its apex referred to as the micropyle. The micropyle opening allows the pollen tube

Pollen tube

The pollen tube of most seed plants acts as a conduit to transport sperm cells from the pollen grain, either from the stigma to the ovules at the base of the pistil, or directly through ovule tissue in some gymnosperms ....
to enter the ovule for fertilization. In gymnosperms (e.g. conifers), the pollen

Pollen

Pollen is a fine to coarse powder consisting of Gametophyte , which produce the male gametes of spermatophyta. A hard coat covering the pollen grain protects the sperm cells during the process of their movement between the stamens of the flower to the pistil of the next flower....
itself is drawn into the ovule and the micropyle opening closes after pollination. During germination

Germination

Germination is the process whereby growth emerges from a period of dormancy. The most common example of germination is the sprouting of a seedling from a seed of an flowering plant or gymnosperm....
, the seedling

Seedling

A seedling is a young plant sporophyte developing out of a plant embryo from a seed. Seedling development starts with germination of the seed....
's radicle

Radicle

In botany, the radicle is the first part of a seedling to emerge from the seed during the process of germination. The radicle is the embryonic root of the plant, and grows downward in the soil....
emerges through the micropyle.

Located opposite from the micropyle is the chalaza
Chalaza

The chalaza is a structure inside animal egg s and plant ovules. It attaches or suspends the yolk or nucellus within the larger structure....
where the nucellus is joined to the integuments. Nutrients from the plant travel through the phloem

Phloem

In vascular plants, phloem is the living Biological tissue that carries organic nutrients , particularly sucrose, a sugar, to all parts of the plant where needed....
of the vascular system to the funiculus and outer integument and from there apoplastically

Apoplast

Within a plant, the apoplast is the free diffusional space outside the plasma membrane. It is interrupted by the Casparian strip in roots, air spaces between plant cells and the cuticula of the plant....
and symplastically

Symplast

The symplast of a plant is the inner side of the plasma membrane in which water can freely diffusion.The plasmodesmata allow the direct flow of small molecules such as sugars, amino acids and ions between cells....
through the chalaza to the nucellus inside the ovule. In chalazogamous plants, the pollen tubes enter the ovule through the chalaza instead of the micropyle opening.

Nucellus, megaspore and perisperm

The nucellus (plural: nucelli) is the central portion of the ovule inside the integuments. It consists of diploid maternal tissue and has the function of a megasporangium

Sporangium

A sporangium is a plant or fungus structure producing and containing spores. Sporangia occur in Flowering plant, gymnosperms, ferns, fern allies, bryophytes, Algaee, and Fungus....
. In immature ovules, it contains a megasporocyte (megaspore mother cell), which undergoes sporogenesis

Sporogenesis

Sporogenesis is the production of spores in biology. The term is also used to refer to the process of reproduction via spores. Reproductive spores are formed in many Eukaryote organisms, such as plants, algae and Fungus, during their normal reproductive Biological life cycle....
via meiosis

Meiosis

In biology or life science, meiosis is a process of reductional division in which the number of chromosomes per cell is halved. In animals, meiosis always results in the formation of gametes, while in other organisms it can give rise to spores....
. Three of the four haploid cells produced in meiosis degenerate, leaving one surviving megaspore inside the nucellus. After fertilization, the nucellus develops into the perisperm that feeds the embryo. In some plants, the diploid tissue of the nucellus can give rise to a seed through a mechanism of asexual reproduction

Asexual reproduction

Asexual reproduction is reproduction which does not involve meiosis, ploidy reduction, or fertilization. Only one parent is involved in asexual reproduction....
called nucellar embryony

Nucellar embryony

Nucellar embryony is a form of seed reproduction that occurs in certain plant species, including many citrus varieties. During the germination of seeds from plants that possess this genetic Trait , the nucellar tissue which surrounds the embryo sac can produce additional embryos which are genetically identical to the parent plant....
.

Megagametophyte and embryo sac

The haploid megaspore inside the nucellus gives rise to the female gametophyte

Gametophyte

In plants and algae that undergo alternation of generations, a gametophyte is the multicellular structure, or phase, that is haploid, containing a single set of chromosomes:...
(megagametophyte). In gymnosperms, the female gametophyte consists of around 2000 nuclei and forms archegonia

Archegonium

An archegonium , from the ancient Greek ???? and ????? , is a multicellular structure or organ of the gametophyte phase of certain plants producing and containing the ovum or female gamete....
which produce the egg cells for fertilization. In flowering plants, the megagametophyte, also referred to as embryo sac, is much smaller and typically consists of only seven cells and eight nuclei. The embryo sac develops from the megaspore through three rounds of mitotic

Mitosis

Mitosis is the process in which a eukaryotic cell separates the chromosomes in its cell nucleus, into two identical sets in two daughter nuclei....
divisions. The cell closest to the micropyle opening of the integuments differentiates into the egg cell, with two synergid cells by its side that may be involved in the production of signals that guide the pollen tube. Three antipodal cells form on the opposite (chalazal) end of ovule and later degenerate, serving no obvious function. The large central cell of the embryo sac contains two polar nuclei.

Zygote, embryo and endosperm

The pollen tube releases two sperm

Sperm

The term sperm is derived from the Greek word sperma and refers to the male reproductive Cell . In the types of sexual reproduction known as anisogamy and oogamy, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell....
nuclei into the ovule. In gymnosperms, fertilization occurs within the archegonia produced by the female gametophyte. While it is possible that several egg cells are present and fertilized, typically only one zygote

Zygote

Embryo

An embryo is a multicellular organism ploidy eukaryote in its earliest stage of development, from the time of first cell division until birth, Egg , or germination....
as the resources within the seed are limited.

In flowering plants, one sperm nucleus fuses with the egg cell into a zygote, the other fuses with the two polar nuclei of the central cell to give rise to the triploid endosperm

Endosperm

Starch

File:Amylose2.svgFile:Amylopektin Sessel.svgStarch or amylum is a polysaccharide carbohydrate consisting of a large number of glucose units joined together by glycosidic bonds....
, protein

Protein

Proteins are organic compounds made of amino acids arranged in a linear chain and joined together by peptide bonds between the carboxyl and amino groups of adjacent amino acid Residue ....
s and oil

Oil

An oil is a chemical substance that is in a viscosity liquid state at room temperature or slightly warmer, and is both hydrophobic and lipophilic ....
s in the endosperm as a food source for the developing embryo and seedling, serving a similar function to the yolk of animal eggs. The endosperm is also called the albumen of the seed.

Ovule

Location within the plant

Ovule parts and development

Integuments, micropyle and chalaza

Nucellus, megaspore and perisperm

Megagametophyte and embryo sac

Zygote, embryo and endosperm

See also