Explain the development of the zygote into an embryo and of the primary endospermic nucleus into an endosperm in a fertilised embryo sac of a dicot plant. Give diagram also.
In plants, fertilization is defined as the fusion of the male and the female gamete to develop into a diploid zygote. After fertilization, a series of events occurs in the zygote to develop into a seed. These are known as post-fertilization events.
Post-fertilization is a series of events that takes place after fertilization to develop a seed from an ovule and a fruit from an ovary. The following events occur in post-fertilization.
- Endosperm development
- Embryogeny
Embryogeny
Embryogeny is defined as the process of growth and development of an embryo from a zygote in the flowering plants. Embryo development stages are the same in both monocot and dicot plants. In dicot plant embryo, an embryonal axis and two cotyledons are present. Two parts are present in the embryonal axis. These are as follows:
- Epicotyl: It is located above the cotyledon level.
- Hypocotyl: It is located below the cotyledon level.
A monocot plant embryo consists of only one cotyledon. The cotyledon is termed as scutellum in the grass family. Root cap of grass is covered with an undifferentiated sheath which is called as coleorhiza. A portion of the embryonic axis, which is located above the scutellum is called epicotyl. Epicotyl consists of shoot apex and coleoptiles.
Endosperm
The endosperm is a type of tissue, which is present in the seeds of flowering plants during the time of fertilization. Reserve food materials fill in the cells of endosperm tissue. It provides nutrition to the developing embryo in the form of starch. Endosperm development is classified into three types. These are as follows:
- Nuclear endosperm formation: In this process, the primary nucleus of endosperm undergoes a nuclear division repeatedly to produce free nuclei without wall formation.
- Cellular endosperm formation: During nuclear division, the formation of cell wall occurs and it leads to the cellular endosperm formation.
- Helobial endosperm formation: It is an intermediate type of endosperm formation between cellular and nuclear type endosperm formation.
During seed maturation or in the mature seed, the developing embryo may either utilize the endosperm completely or it is used by seed during seed germination.
