Sexual Reproduction in Flowering Plants: Post-Fertilisation and Apomixis

Flashcards covering post-fertilisation developments including endosperm types, embryo structure in dicots and monocots, seed classification, fruit types, and special reproductive mechanisms like apomixis and polyembryony.

What structures and events are collectively termed post-fertilisation events?

Following double fertilisation, events of endosperm and embryo development, maturation of ovule(s) into seed(s), and ovary into fruit are collectively termed post-fertilisation events.

Why does endosperm development precede embryo development?

The primary endosperm cell (PEC) divides to form a triploid endosperm tissue filled with reserve food materials used for the nutrition of the developing embryo.

What is free-nuclear endosperm, and what is a common example of it?

It is a stage where the PEN undergoes successive nuclear divisions to give rise to free nuclei. The coconut water from tender coconut is a common example, made up of thousands of nuclei.

Distinguish between the two parts of a coconut in terms of endosperm type.

The coconut water is free-nuclear endosperm, while the surrounding white kernel is the cellular endosperm.

Which plants serve as examples of seeds where endosperm is completely consumed by the developing embryo?

Pea, groundnut, and beans.

Which plants serve as examples of seeds where endosperm persists in the mature seed?

Castor and coconut.

What is the sequence of stages in dicotyledonous embryogeny starting from the zygote?

The zygote gives rise to the proembryo, and subsequently to the globular, heart-shaped, and mature embryo.

Define epicotyl and hypocotyl in a typical dicotyledonous embryo.

The epicotyl is the portion of the embryonal axis above the level of cotyledons (terminating in the plumule), and the hypocotyl is the cylindrical portion below that level (terminating in the radicle).

What is the specific name for the cotyledon in the grass family, and where is it located?

It is called the scutellum and is situated towards one side (lateral) of the embryonal axis.

What are the coleorrhiza and the coleoptile?

The coleorrhiza is an undifferentiated sheath enclosing the radicle and root cap; the coleoptile is a hollow foliar structure enclosing the shoot apex and leaf primordia.

Distinguish between non-albuminous and albuminous seeds.

Non-albuminous seeds have no residual endosperm as it is completely consumed (e.g., pea, groundnut); albuminous seeds retain a part of the endosperm (e.g., wheat, maize, barley, castor).

What is perisperm, and in which plants is it found?

Perisperm is the residual, persistent nucellus found in seeds such as black pepper and beet.

What is the moisture content of a mature, relatively dry seed, and what state does the embryo enter?

The water content is reduced to $10-15\%$ moisture by mass, and the embryo may enter a state of inactivity called dormancy.

What is the pericarp?

The pericarp is the wall of the fruit which develops from the wall of the ovary.

What are false fruits, and what are some examples?

False fruits are those where the thalamus also contributes to fruit formation; examples include apple, strawberry, and cashew.

Define parthenocarpic fruits and provide an example.

Fruits that develop without fertilisation are called parthenocarpic fruits; an example is the banana.

How long did the seeds of Lupinus arcticus and Phoenix dactylifera remain viable according to the records?

Lupinus arcticus remained viable for an estimated $10,000$ years of dormancy, while Phoenix dactylifera was found to be viable after $2,000$ years.

What is apomixis, and in which plant families is it common?

Apomixis is a special mechanism to produce seeds without fertilisation, commonly found in species of Asteraceae and grasses.

What is polyembryony?

Polyembryony is the occurrence of more than one embryo in a seed, frequently seen in Citrus and Mango varieties where nucellar cells develop into embryos.

Why is apomixis significant for the hybrid seed industry?

If hybrid plants are made into apomicts, there is no segregation of characters in the progeny, allowing farmers to use the hybrid seeds to raise new crops year after year without buying new seeds.