Development of flower

The flower is a plant’s reproductive organ. They are not only involved in reproduction but also serve as a food supply for other living organisms. They have a lot of nectar to offer. The sepals, petals, stamens, and pistils all make up a whole flower. An incomplete flower, on the other hand, is one that lacks one or more of these structures. 

Structure:

The following are the various parts of a flower:

Vegetative parts of flower:

The vegetative parts consists of the following:

1. Petals: Bees, insects, and birds are drawn to this brightly coloured section. Petal colour varies from plant to plant; some are vivid, while others are pale. As a result, petals assist us in distinguishing one bloom from another. 

2. Sepals: The green-colored region beneath the petals that protects emerging buds is known as the sepal. Some flowers have merged petals and sepals, whereas others have petals and sepals that are separated. 

Reproductive parts of flower:

Flowers house the reproductive organs of the plant. The amount of petals, sepals, stamens, and pistils can vary amongst plants. The existence of these parts distinguishes a complete flower from an incomplete flower. A flower also has reproductive organs, such as stamen and pistil, in addition to these. A flower can have all female parts, all male parts, or mixed male and female parts. A flower’s reproductive parts include the following: 

1. Stamen: Androecium is the name given to the male reproductive organ. It is made up of two parts: anther and filaments. 

• Pollen generation and storage are carried out by the anther, which is a yellowish sac-like structure. 

• The filament is a thin, threadlike structure that helps the anther to stay alive.

2. Pistil: This is the flower’s deepest section and female reproductive organ, which is made up of three parts: stigma, style, and ovary. 

• Stigma: In the gynoecium of a flower, it is the highest section or receptive tip of carpels. 

• Style: The stigma and the ovary are connected by a long tube-like thin stalk. 

• Ovary: The ovary is a ductless reproductive gland that contains a large number of ovules. It’s the section of the plant where the seeds are produced. 

Development of flowers:

Each stalk of flowering plants has a meristem, which is a collection of undifferentiated pluripotent cells at its developing tip. The meristem produces the stalk that supports the shoot, as well as a succession of leaves on its flanks, as the shoot grows. 

The branch eventually produces flowers, which is when it is referred to as an inflorescence. Flowers appear when bracts (small leaf-like organs) join the stem or on the shoot meristem’s flanks. They appear as tiny meristems that are comparable to shoot meristems in many aspects. 

Instead of developing leaves on their flanks, they produce floral organs, which start off as undifferentiated primordia and grow into one of four types of mature organs. Within the blooms of related species, each organ type appears in predetermined places and quantities that are relatively stable. 

ABC model of flower development:

The number of chromosomes is reduced from a diploid number (2n) to a haploid number (n) during the initial stage of sexual reproduction, “meiosis” (n). Haploid gametes combine to create a diploid zygote during “fertilisation,” and the original number of chromosomes is restored.

In angiosperms, the ABC model of flower formation reveals the presence of three classes of genes that control the development of floral parts. Class A genes, class B genes, and class C genes are the three types of genes. Floral organ development is induced by these genes and their interactions.

The ABC model is based on the observation that mutations cause proper floral organs to develop in the wrong whorls and is formulated using molecular genetics.

There are normally four concentric whorls of organs in angiosperm flowers, namely sepal, petal, stamen, and carpel, which are generated in whorl 1, whorl 2, whorl 3, and whorl 4, with whorl 1 on the periphery.

When class A genes are expressed in the whorl 1, they cause the development of sepals. Petal development in whorl 2 is induced by the interactions of class A and class B genes. The combination of class B and class C genes results in the formation of stamens in whorl 3.

Carpel development is induced by the class C gene in whorl 4. The ABC paradigm states that class A genes combined and class C genes alone are responsible for sepal and carpel development, respectively. To determine the development of petals, the class B and class A genes work together. Stamen formation is induced by the interaction of the class B and class C genes.

The ABC model was developed by Coen et al. (1991). While researching mutations that alter flower structure. The class ABC genes that control floral development were discovered by Coen et al. They also developed molecular models for determining floral meristem and organ identification. They discovered that distantly related angiosperm plants use similar methods to produce floral organ patterns. Arabidopsis thaliana and Antirrhinum majus are two examples.

The following two factors influenced the development of the ABC model:

1. The identification of homeotic mutants (homeotic genes recognise certain floral organs and aid in the development of the organ in its proper whorl). The homeotic mutant expresses itself incorrectly, causing the right organ to develop in the wrong whorl. Petals, for example, arise in the whorl where stamens would ordinarily develop).

2. The discovery that each of the genes that cause the creation of an organ in a flower has an effect on either the sepal and petals or the petals and stamens groups of floral organs. Homeotic genes are those that belong to the classes A, B, and C. They determine the identity of various floral organs and cause them to develop in their appropriate whorls.

The homeotic mutants exhibit faults in floral organ development, causing the proper organs to develop in the wrong whorls/places, i.e. one floral organ develops in the whorl where another floral organ would normally develop. Petals, for example, grow in the whorl where stamens would ordinarily emerge.

One or more homeotic genes are found in each whorl of a flower, and their cooperative functions dictate which organ will be developed in that whorl. The activity of class A genes, for example, is restricted to whorls 1 and 2. In whorls 2 and 3, the class B genes play a role. In whorls 3 and 4, the class C gene is active.

From flowers to fruits:

When pollen reaches the stigma, it forms a pollen tube, which allows sperm to go down the style and fertilise the ovule; fertilised ovules mature into seeds. Fertilisation is the flower’s death, as the petals drop or wither and the ovary begins to expand and develop into what we call fruit. 

Conclusion:

In the blooms, gametophytes grow. Without fertilisation, the blooms might develop diaspores. The flower’s ovary develops into a fruit with a seed after fertilisation. Flowers’ most crucial function is reproduction. Selfing, or the union of sperms and eggs from the same flower, or cross-fertilization, or the union of sperms and eggs from separate flowers, may be encouraged by flowers.