Sexual Reproduction in Flowering Plants - Post-fertilization: Development of Endosperm and Embryo
Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Post-fertilization events include the development of endosperm and embryo, maturation of ovule(s) into seed(s), and ovary into fruit.
Endosperm development precedes embryo development to ensure a steady supply of nutrition for the developing embryo.
The Primary Endosperm Nucleus () undergoes successive nuclear divisions to give rise to free nuclei. This stage is called free-nuclear endosperm (e.g., the water in a tender coconut).
Subsequently, cell wall formation occurs, and the endosperm becomes cellular (e.g., the white kernel in coconut).
Embryogeny refers to the stages of embryo development. In dicots, the zygote () gives rise to the proembryo, then to the globular, heart-shaped, and finally the mature embryo.
A typical dicotyledonous embryo consists of an embryonal axis and two cotyledons. The portion of the embryonal axis above the level of cotyledons is the epicotyl, which terminates with the plumule ().
The cylindrical portion below the level of cotyledons is the hypocotyl, which terminates at its lower end in the radicle () covered by a root cap.
Monocotyledonous embryos possess only one cotyledon. In the grass family, it is called the scutellum, situated towards one side of the embryonal axis.
In monocots, the radicle and root cap are enclosed in an undifferentiated sheath called coleorhiza, and the plumule is enclosed in a hollow foliar structure called coleoptile.
Seeds can be non-albuminous (no residual endosperm, e.g., pea, groundnut) or albuminous (retain a part of endosperm, e.g., wheat, maize, castor).
📐Formulae
💡Examples
Problem 1:
If the chromosome number in the leaf cells of a female plant is and the male plant is , calculate the number of chromosomes in the endosperm of the resulting seed.
Solution:
The endosperm is formed by the fusion of two polar nuclei from the female and one male gamete. Female plant . Male plant . Endosperm ploidy = .
Explanation:
In triple fusion, the is formed by polar nuclei (each from the female parent) and male gamete ( from the male parent). Thus, chromosomes.
Problem 2:
Contrast the endosperm of a coconut with that of a pea seed at maturity.
Solution:
In coconut, the endosperm is persistent and exists as both liquid (nuclear) and solid (cellular) forms. In pea, the endosperm is completely consumed by the developing embryo during seed maturation.
Explanation:
Pea is a non-albuminous (exalbuminous) seed, whereas coconut is an albuminous seed where endosperm provides nourishment during germination.