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Course: The life of plants - Class 11 > Unit 4
Lesson 4: Post-fertilization events, apomixis, and polyembryonyPost-fertilization events: endosperm, embryo, seed, and fruit
Development of endosperm, embryo, seed, and fruit after double fertilization.
This article offers and overview of the post-fertilization development of endosperm, embryo, seed, and fruit from a fertilized flower.
Key terms
| Term | Meaning |
|---|---|
| endosperm | the tissue that forms in the primary endosperm cell after triple fusion |
| PEN | primary endosperm nucleus |
| free-nuclear endosperm | stage at which the endosperm tissue consists of free nuclei, after undergoing nuclear division, but not cell wall formation |
| cellular endosperm | stage at which endosperm tissue has formed cell walls around the free nuclei |
| albuminous seed | mature seed that has residual endosperm |
| non-albuminous seed | mature seed that no longer has residual endosperm |
| perisperm | residual nucellus in seeds |
| pericarp | wall of fruit that develops from wall of ovary |
| true fruits | fruits that develop only from the fertilized ovary |
| false fruits | fruits that develop from multiple parts of the flower, and not just the ovary |
| parthenocarpy | development of fruit without fertilization of the flower |
What are post-fertilization events?
Where do baby plants come from? You might know that seeds can be give rise to new plants. But where do we get seeds? Once a flower has been successfully pollinated and fertilized, parts of it eventually develop to form the fruit, seed, etc.
Let's take a closer look at some of these structures - the endosperm, embryo, seed and fruit. Interestingly, they develop in sequence; first comes the endosperm, then the embryo, and finally the seed and fruit.
Endosperm
At the end of double-fertilization, the primary endosperm cell contains the primary endosperm nucleus (PEN). Most often, the PEN will first undergo repeated nuclear divisions to produce a tissue called the free-nuclear endosperm. Later, cell walls develop around the free nuclei to create cellular endosperm. This tissue surrounds the embryo, and provides it with nutrition.
In some species such as the pea or bean plants, the embryo uses up its endosperm as it develops. In others like the castor bean, wheat, maize, and barley plants, the endosperm is still present in the mature seed.
Embryo
The other structure formed at the end of double-fertilization is the zygote. Embryogeny, or embryo development, will usually only begin once there is some amount of endosperm available for nourishment.
Both monocots and dicots share similarities in the initial stages of embryogeny. In both cases, the zygote divides to form a proembryo, which gives rise to a mature embryo. Typically, the embryo has an embryonal axis, a radicle, and a root tip or cap.
Seed
The fertilized ovule, or seed, develops last, along with the transformation of the ovary into fruit. Here are some common features of seeds:
- Depending on the species of plant, a typical seed has one or more seed coat (formed from the integuments of the ovule), one or more cotyledons, and an embryo axis.
- Mature seeds can be non-albuminous (no endosperm present), or albuminous (retains endosperm).
- In some cases, like black pepper and beets, remnants of the nucellus can be found (perisperm).
The micropyle remains as a pore in the seed coat, to allow the exchange of water and oxygen with the environment. Mature seeds dry out and slow down the metabolic activity of the embryo. This allows the seed to germinate under favourable conditions, or remain dormant until that happens.
Fruit
As the ovule forms the seed, the walls of the ovary become the pericarp, or walls of the fruit. Most often, the petals of the flowers fall off during this time, and the fruit develops only from the ovary (true fruits such as grapes and figs). In some others like apples, strawberries and cashews, other parts of the flower also develop into the fruit (false fruits).
In some cases, fruits can develop without fertilization occurring at all. This is known as parthenocarpy (eg. banana).
That's a lot of information we've just learnt about seeds and fruits. Let's take a few refreshers.
Click on the little grey circles in the top right corner, next to "test your understanding" to move onto subsequent questions.
Want to join the conversation?
what is coleorrhiza and coleoptile ?(3 votes)
The coleoptile protects the stem and leaf when it emerges from under the soil. Coleorihza is a root sheath. It's a layer of tissue that connects the coleoptile to the primary root(2 votes)