1. Embryology of Angiosperms by Sheikh Abdul Shakoor Assistant Professor (Botany) Govt. Degree College, Kulgam

2. INTRODUCTION
The process of sexual reproduction and the related events in the life history of an organism are studied under the branch of Embryology.
Embryology includes the study of structure and development of reproductive organs, gamete formation, fertilization, embryo development and formation of new plant.
Professor P. Maheshwari of Delhi University is regarded as father of Embryology in India.

3. FLOWER
Flower is a modified shoot of determinate growth evolved as a result of several hormonal and structural changes.
A flower has highly condensed internodes and leaves, specialized variously to act as different floral organs like
Sepals (Calyx)
Petals (Corolla)
Stamens (Androecium)
Carpels (Gynoecium)
It serves as an important organ for the sexual propagation of the angiosperms. A typical flower has four whorls in the form of calyx, corolla, androecium and gynoecium .

4. CALYX and COROLLA
CALYX: It is outermost whorl of the flower and its units are called as sepals. The sepals are green in color with leafy texture. The primary function of calyx is protection of inner floral whorls during bud condition. Recently, it has been reported that some nitrogenous substances are secreted by sepals which are helpful in post-pollination development of the ovary (Fig.1a).
COROLLA: It represents the second whorl of the flower and its units are called as petals. The petals are brightly colored leafy structures that help in protection and mainly the pollination, by attracting insects due to their attractive colors and curious forms (Fig.1a).
Both calyx and corolla does not directly participate in the process of sexual reproduction and hence are known as accessory whorls.

5. ANDROECIUM and GYNOECIUM
ANDROECIUM: It is the male reproductive whorl of a flower and its units are known as stamens. A stamen is having anther, filament and connective as its parts. Anther is fertile part in which microspores or pollens are produced. Filament of the anther is attached to the thalamus or to the petals.
GYNOECIUM: It is the female reproductive whorl and its units are known as carpels/pistils. Each carpel consists of three parts- stigma, style and ovary. Ovary is the basal swollen region which bears the ovules.
ANDROECIUM and GYNOECIUM take part in the process of reproduction directly and hence are known as essential whorls of a flower.

6. PROCESS OF SEXUAL REPRODUCTION
MICROSPROGENESIS: The process of formation of Microspores/pollen grains from the microspore mother cell inside the microsporangium (pollen sac) is known as Microsporogenesis.
MICROGAMETOGENESIS: This involves the formation of male gametes from the microspore.
MEGASPOROGENESIS: The process of formation of megaspores from megaspore mother cell inside the megasporangium (ovule).
MEGAGAMETOGENESIS: The events involving the formation of embryo sac from megaspore are included in this process.

7. PROCESS OF SEXUAL REPRODUCTION
POLLINATION: It is the process during which pollen grains are transferred from anther to stigma of the same flower or different flower on the same or different plant.
FERTILIZATION: The process of fusion of male and female gametes to form zygote is known as fertilization. The angiosperms are characterized by double fertilization that includes an additional fertilization act between one of the male gametes and the polar nuclei present in the central cell of the embryo sac. It is also known as triple fusion and results into the formation of primary endosperm nuclei (PEN) and finally the endosperm.
ENDOSPERM FORMATION: The process during which endosperm is developed from the primary endosperm nuclei formed as a result of triple fusion. It is a nutritive tissue meant for the nourishment of the developing embryo.
EMBRYOGENESIS: The process of formation of embryo from zygote constitutes the embryogenesis or embryogeny.

8. STRUCTURE OF ANTHER Anther is the fertile portion of the stamen.
Each anther is having a column of sterile tissue known as connective and on either side of this connective is an anther lobe.
An anther with two anther lobes is called a dithecous anther.
Each anther lobe is usually having 2 chambers or pollen sacs called microsporangia and thus there are generally four microsporangia in an anther (Tetrasporangiate).
However, at maturity the two microsporangia of an anther lobe get united by dissolution of partition wall between them.
In some plants (e.g., Malvaceae family) anther is having only single anther lobe and hence only two microsporangia. Such anthers are known as monothecous anthers.

9. STRUCTURE OF ANTHER

10. STRUCTURE OF ANTHER
The detailed structure of anther in transverse section shows following structural details:
Parietal layers or Wall layers:
Pollen chamber or microsporangia having sporogenous tissue.

11. PARIETAL WALL LAYERS
Epidermis: This is the outermost layer of anther wall and is only one cell in thickness. This layer is greatly stretched and flattened at maturity and performs the usual function of protection.
Endothecium: It is a single layer of radially elongated cells just below the epidermis. The cells of this layer possess cellulosic fibrous thickenings arising from their inner walls and are hygroscopic in nature. These fibrous thickenings help in dehiscence of anther. The cells from where dehiscence starts are without fibrous thickenings and are thin walled. These thin walled cells collectively form the Stomium. In family Hydrocharitaceae fibrous thickenings are absent.
Middle layers: Three or four layers of thin walled cells inner to endothecium are nown as middle layers. In family Najadaceae and Lamnaceae middle layers are absent.These layers disintegrate at maturity.

12. PARIETAL WALL LAYERS
Tapetum: This is the innermost wall layer of the anther and the cells of this layer are having large nuclei and dense cytoplasm. This layer is of great physiological importance as most of the food material from outside passes through this layer. At maturity the cells of this layer disintegrate and provide nourishment to the developing microspores. DNA content of the tapetal cells is enormously increased due to some abnormal divisions like endomitosis, polyteny and by the formation of restitution nucleus. Tapetum is of following two types:
Amoeboid or plasmodial: The cells of this type of tapetum separate from the anther wall and enter freely into the pollen chamber.
Secretory or glandular: The cells of this type of tapetum remain in contact with the anther wall throughout. This is the most common type of tapetum in angiosperms.

13. FUNCTION OF TAPETUM
It provides nourishment to the developing pollen grains. Additionally, it also secretes some substances of utmost importance as:
Callase enzyme: This enzyme helps in breaking the callose material which unite the pollen grains in the pollen tetrad and help in the separation of the individual pollens.
Ubish bodies: These are substances of lipoidal nature and form a layer on pollen grains. This layer serves as a substratum (base) for the deposition of sporopollenin which forms the outer wall of the pollen grains. Ubish bodies are secreted only by the glandular tapetum.
Pollen kitt substances: It is the outermost oily, thick, viscous and sticky material present on the surface of entomophilous pollens. Pollen kit is chiefly composed of lipids and carotenoids. It acts as an insect attractant and protect the pollens from UV radiations.

14. POLLEN CHAMBER OR MICROSPORANGIA
Inside the wall layers, pollen chamber or microsporangia are present. These microsporangia bear sporogenous or archesporial cells which gives rise to microspores during the process of microsporogenesis.

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