Fruit and Seed Development

Following fertilization, several physiological and morphological changes occur in the flower. These changes are observed in the zygote, endosperm, and ovary. The structures of the flower that are no longer required for fertilization, such as the calyx, corolla, and androecium (male reproductive parts), undergo significant changes or eventually wither away.

Even dead pollen grains play an important role in some cases by triggering certain changes that happen after fertilization, such as fruit development. The fruit formation requires hormones that come from the decaying pollen grains.

After fertilization, the zygote undergoes rapid mitotic divisions and becomes a multicellular embryo. This embryo will differentiate into three parts:

1. Plumule – the young shoot (future stem and leaves).
2. Radicle – the young root.
3. Cotyledons – the seed leaves that serve as food reserves for the developing embryo.

In dicot plants, there are two cotyledons, while in monocots, there is only one cotyledon.

The fertilization process leads to the formation of the endosperm, a tissue that serves as a food source for the embryo. The primary endosperm nucleus, which is triploid (3n), undergoes mitosis to develop into a mass of endosperm tissue.

• Endospermic seeds, such as maize, wheat, and rice, contain endosperm that serves as a food source.
• Non-endospermic seeds, like legumes (e.g., beans), rely on the cotyledons for food storage, and the endosperm may be absorbed or disappear as the seed matures.

The integuments of the ovule, which are the protective layers around the seed, develop into a tough outer covering known as the seed coat or testa. The micropyle, a small opening in the seed coat, remains and allows water and oxygen to enter during seed germination.

During the final stages of seed development, the seed undergoes a reduction in water content, which helps the seed enter a state of dormancy. Seed dormancy is essential because it helps the seed survive unfavorable conditions until the environment is suitable for germination.

Once fertilization occurs, the ovary of the flower develops into a fruit. The wall of the ovary becomes differentiated into three layers:

1. Exocarp – the outermost layer of the fruit.
2. Mesocarp – the fleshy middle layer.
3. Endocarp – the innermost layer surrounding the seed.

These three layers together form the pericarp, which is distinct in fleshy fruits but may fuse in dry fruits.

For the ovary to properly mature into a fruit, it requires hormones produced by the decaying pollen grains. If there aren't enough pollen grains available after fertilization, the ovary might not develop into a fruit. The style (female part) also withers and falls off, leaving a scar on the fruit.