Post-Fertilisation Changes: Endosperm and Embryo Development

After fertilisation, a flower undergoes major changes. The zygote develops into an embryo, the primary endosperm cell forms endosperm, the ovule becomes the seed, and the ovary becomes the fruit. These are called post-fertilisation changes.

These changes matter because seeds are the main means of reproduction and dispersal for flowering plants, and fruits protect seeds and help them spread. Almost all grains, pulses, fruits, and vegetables we eat are products of post-fertilisation development.

Key Concepts

Endosperm development: Repeated division of the triploid primary endosperm cell to form nutritive tissue. It can be nuclear, cellular, or helobial type.

Embryogenesis: Development of the diploid zygote into a mature embryo with cotyledons, plumule, and radicle.

Seed: Mature ovule containing embryo, stored food, and protective seed coat from integuments.

Fruit: Mature ovary, often with other floral parts, that protects seeds and aids dispersal.

Pericarp: Fruit wall developed from ovary wall, differentiated into epicarp, mesocarp, and endocarp in many fruits.

Dormancy: Resting phase of mature seed before germination.

How It Works

1. The primary endosperm cell divides rapidly, often before the zygote divides much.
2. Endosperm may remain as storage tissue or be consumed by developing cotyledons.
3. The zygote divides to form a proembryo, then globular, heart shaped, and mature embryo stages in dicots.
4. In monocots, the embryo has one cotyledon called scutellum.
5. Integuments harden into seed coat. The micropyle remains as a small pore.
6. The ovary wall grows into pericarp. Sepals, petals, and stamens usually fall off.

Worked Example

A pea flower has an ovary with 8 ovules. After fertilisation, 6 ovules develop into seeds. Seed set percentage is 6 divided by 8 multiplied by 100 equals 75 percent. If each mature seed weighs 0.4 gram, total seed weight per pod is 6 multiplied by 0.4 equals 2.4 grams. If a plant produces 50 such pods, estimated seed yield is 50 multiplied by 2.4 equals 120 grams per plant. This links ovule number to final yield.

Common Misconceptions

• Fruit always means a sweet edible structure. Botanically, grains, pods, and nuts are also fruits if they develop from the ovary.
• Endosperm is present in all mature seeds. In pea and bean it is consumed early and cotyledons store food.
• Seed and fruit form independently. Seed formation from ovule and fruit formation from ovary happen together after fertilisation.

Real-World Applications

Grain production depends on proper endosperm filling in wheat, rice, and maize. Fruit growers thin excess fruits so remaining fruits get more resources and grow larger. Seed producers test embryo development to ensure viability. Parthenocarpy, fruit without fertilisation, is used for seedless bananas and grapes but is different from normal post-fertilisation fruit set.

Post-fertilisation changes convert a flower into seeds enclosed in fruit. Endosperm feeds the embryo, the embryo becomes the next plant, and the fruit ensures protection and dispersal.