Flowering in plants

What are flowers?

Flowers are the reproductive structures of angiosperms, defined by developmental programming.

Why is flowering such an important decision for plants?

Flowering determines reproductive success and must be timed to maximise pollination, seed quality, and survival.

What is a meristem?

A meristem is a region of actively dividing cells that produces new tissues and organs.

What key transition occurs before flowering?

The transition from vegetative meristem identity to reproductive (floral) meristem identity.

What controls the transition to flowering at the molecular level?

Differential expression of homeotic genes.

How many whorls are in an Arabidopsis flower?

Four whorls.

What organs are found in each floral whorl?

• Sepals

• Petals

• Stamens

• Carpel

What is the function of sepals?

Protection of the developing flower bud.

What is the function of petals?

Attract pollinators.

What are stamens and carpels?

Stamens are male reproductive organs; carpels are female reproductive organs.

Why must flowering be tightly regulated?

To coincide with pollinators, suitable partners, and favourable environmental conditions.

What risks are avoided by correct flowering time?

Frost damage, poor seed set, and wasted energy.

How do plants decide when to flower?

By integrating environmental, developmental, and endogenous signals.

Name the major flowering pathways in Arabidopsis.

• Photoperiodic

• Vernalization

• Autonomous

• Gibberellin

What is FLC?

A floral repressor gene that inhibits flowering.

How does vernalization affect flowering?

Prolonged cold exposure represses FLC, allowing flowering to occur.

What does “vernalization” mean?

The removal of a flowering block through exposure to cold.

What is photoperiodism?

The response of plants to day length.

What role does the circadian clock play in flowering?

It measures day length and regulates flowering genes accordingly.

Name key genes in the photoperiodic pathway.

GI, CO, FT, SOC1, LFY.

Where is FT produced?

In the leaves.

What is FT also known as?

Florigen.

What is florigen?

A graft-transmissible flowering signal produced in leaves.

Who first proposed the concept of florigen?

Mikhail Chailakhyan in the 1930s.

How does florigen act?

FT protein moves from leaves to the shoot apical meristem to induce flowering.

How was FT movement experimentally demonstrated?

Using grafting and fluorescent protein tagging.

What types of photoreceptors exist in Arabidopsis?

• Phytochromes (A–E)

• Cryptochromes (1–3)

• Phototropins (1–2)

Why are photoreceptors important for flowering?

They allow plants to detect light quality and day length.

What is forward genetics?

Identifying genes by screening for mutants with altered phenotypes.

How are mutations commonly induced in plants?

Using chemicals (EMS), radiation, or T-DNA insertion.

What does the ABC model explain?

How floral organ identity is specified.

How many classes of genes are in the ABC model?

Three: A, B, and C.

What organs are specified by A-function genes?

Sepals.

What organs are specified by A + B genes?

Petals.

What organs are specified by B + C genes?

Stamens.

What organs are specified by C-function genes?

Carpels.

How do A and C genes interact?

They act antagonistically to define boundaries.

Why was the ABC model expanded?

To explain additional complexity in floral development.

What do E-class genes (SEPALLATA) do?

They act as cofactors required for all floral organ identity functions.

What does the D-class gene control?

Ovule identity.

What are MADS-box genes?

A family of transcription factors controlling floral development.

Which floral identity genes are NOT MADS-box genes?

Some A-class genes such as APETALA2.

Why are MADS-box genes important evolutionarily?

They are highly conserved and allow flexible flower evolution.

What types of flowers does the ABC model best explain?

Radially symmetrical flowers.

What does the ABC model not fully explain?

• Dorsoventral asymmetry

• Temporal control

• Meristem identity

Why is the ABC model still valuable?

It shows how small genetic changes can produce large evolutionary diversity

What is the central idea of flowering regulation?

Flowering is controlled by integrated signalling pathways and gene networks that coordinate timing and organ identity.