Ovule development

Ovule First and foremost, the ovule is a structure found in plants that develops into a seed during the process of reproduction. When it is mature, it contains food tissue, and one or two future seed coats cover it, which we refer to as integuments.

A small opening in the integuments allows the pollen tube to enter and discharge its sperm nuclei into the embryo sac, which is protected by the integuments. Furthermore, a large oval cell in which the process of development and fertilisation takes place. Although they are all attached to their respective stalks, each of these has its own attachment between the base and the funiculus that carries them.

Ovule

A structure that rises within the seed plants and is made up of the female reproductive cells is known as an ovule. It is divided into three sections: The integument is the outer layer of the organism that we refer to as a nucleus. It is also a remnant of the megasporangium.

Structure of Ovule

The ovule is an integument megasporangium, which means it has a thick integument. The stalk and the body are both contained within it. The stalk is referred to as a funicle. It is attached to the placenta at one end, and it is attached to the body of the baby at the other end of the funicle.

The hilum, on the other hand, is the point at which the funicle and the body connect. Many times, the funicle becomes fused with the body of the ovule on one side, resulting in the formation of a ridge that we refer to as a raphe.

The body of the ovule has two ends, one of which is the basal end and the other of which is the upper end, which we also refer to as the micropylar end.

A cover of one or two envelopes surrounds the main body of the ovule, which we refer to as integuments. These leave a small opening at the top of the ovule, which we refer to as a micropyle (small opening). The integuments enclose a large amount of parenchymatous tissue, which we refer to as the nucellus.

Types and development of Ovules 

The ovule of a plant contains a variety of different components, each of which serves a specific function. The Nucellus, Integuments, and the female Gametophyte are the components that make up this structure.

• Nucellus: The nucellus is the largest part of the ovule, and it contains the embryo sac as well as the nutritive tissue of the ovule. Despite the fact that the plants have been fertilised, this nutritive tissue remains in place and provides nutrients to the embryo. It can be found at the center of the flowering plant’s flowering stem.
• Integuments: This is the tough protective layer that surrounds the ovule during development. Because it is an ovule, it serves to protect the seeds. This integument completely encloses the nucleus, but it leaves a small gap known as the micropyle. Most of the time, there is only one integument in an ovule in gymnosperms, whereas angiosperms have two integuments in each of their flowers. 

Within the ovule, the integument is comprised of gamete-producing sexual organs, which are essential for the reproduction of all plants. This haploid female gametophyte, also known as the embryo sac or megagametophyte, is distinguished by the presence of only one unpaired chromosome, indicating that it is a haploid female.

In angiosperms, the female gametophyte is formed from a megagametophyte, and it is referred to as the embryo sac in other species. The megagametophyte produces an egg cell, which is responsible for fertilisation.

Ovule orientation can be anatropous, which means that when the micropyle is inverted, it faces the placenta, campylotropous, amphitropous, orthotropous, or a combination of the above. Because of the integuments that surround it, it appears to be a megasporangium in appearance.

Furthermore, they are generally composed of the diploid maternal tissue, which includes a megasporocyte, as well as other components.In them, the megaspores remain and divide through mitosis to produce the haploid female gametophyte or megagametophyte, which is also retained within them.

The gametophyte is surrounded by the remnants of the megasporangium tissue that once covered it.

Archegonia are produced by the gametophytes, and these are responsible for the production of egg cells. After the fertilisation process, it produces a diploid zygote, which is then used to initiate cell division. After a while, an embryo of the sporophyte begins to take shape.

In flowering plants, a second sperm nucleus fuses with other nuclei in the megagametophyte, resulting in the formation of a polyploid endosperm tissue that is characteristic of the flowering plant. Aside from that, it provides nourishment for the young sporophyte.

Types of Ovules

In a plant, there are six different types of ovules, and these different types of ovules are distinguished by their shapes.

• Chalaza is the area where the nucellus and integuments come together, and it can be either orthotropous or atropous. A plant ovule that is orthotropous is one that has its body lined up straight so that the chalaza, the funicle (which is responsible for attaching the ovule of the plant to the placenta), and the micropyle are all aligned.
• The hilum is a scar that marks the location where the seed was eventually attached to the fruit by the funicle. It is found in anatropous plants. Anatropous ovules are completely inverted throughout development, resulting in a micropyle that is located close to the hilum of the ovule.
• Hemi-Anatropous: In this case, the ovules are arranged at a right angle to the funicle, forming a right triangle. Its shape eventually takes on the appearance of an ovule lying on its side.
• It is believed that the Campylotropous embryo sac is slightly curved as a result of the ovule’s bent shape and the loss of alignment between the chalaza and micropyle that occurs in Campylotropous.
• In the case of the Amphitropous ovule, the body is curved in such a way that the ovule and embryo sac take the shape of a horseshoe when they are combined.
• This is the most distinct of the circinotropous shapes because it has the most distinct shape. In the case of the circinotropous ovule, the funicle is so long that it forms a complete circle around the ovule, with the micropyle pointing upwards at the end of it. In comparison to the other six types of ovules, it is considered to be the most distinctively shaped.

The Ovule’s Functions

During the process of sexual reproduction, it is extremely important. Once a pollen grain lands on the stigma of a flower of a similar species, the pollen grain becomes fertile.

In addition, it sends out a pollen tube through the style, which is located below. The tube then travels through the plant’s ovary until it reaches the ovule inside the fruit.

Once this has occurred, the fertilisation process can begin as the nucleus of the pollen grain is brought down the tube and merges with the nucleus of the embryo sac, which is located within the embryo sac.

Notably, pollen is typically used as a male substitute for this substance. It contains the male gametophytes, as the name suggests.

Conclusion

The ovule is a structure found in plants that develops into a seed during the process of reproduction.It is divided into three sections: The integument is the outer layer of the organism that we refer to as a nucleus. It is also a remnant of the megasporangium.The ovule of a plant contains a variety of different components, each of which serves a specific function. The Nucellus, Integuments, and the female Gametophyte are the components that make up this structure. In a plant, there are six different types of ovules, and these different types of ovules are distinguished by their shapes.The ovule is an integument megasporangium, which means it has a thick integument. The stalk and the body are both contained within it. The stalk is referred to as a funicle. It is attached to the placenta at one end, and it is attached to the body of the baby at the other end of the funicle.