flower development

Question 1

What factors determine the phase transition to flowering in plants?

Answer 1

• Reproductive success is the goal of flowering.
• The transition involves an integration of internal and external cues:
  Internal cues: Plant age.
  External cues: Photoperiod and temperature.
• Morphological and developmental changes occur in the shoot apical meristem (SAM).
• The plant transitions to reproductive growth and the meristem becomes an inflorescence meristem (IM), which eventually produces flowers.

Question 2

What are the key phases of plant development?

Answer 2

• Juvenile phase:
  The plant cannot form reproductive organs.
  Duration varies between species.
• Adult vegetative phase:
  The plant is capable of forming reproductive organs under inductive conditions.
  Changes in leaf morphology, thorniness, and root system occur.
• Adult reproductive phase:
  The plant flowers and produces seeds.

Question 3

What types of meristems are involved in the reproductive phase of plants?

Answer 3

• Inflorescence meristem (IM):
  Produces clusters of flowers; can be determinate or indeterminate.
• Floral meristem (FM):
  Determinate and produces floral organs of a single flower.
  The IM produces small cell mounds that develop into FMs.

Question 4

How is the timing and identity of flowering controlled genetically?

Answer 4

• Flowering time genes:
  Determine when a plant begins to flower, linked to environmental conditions.
  Floral meristem identity genes:
• Commit meristems to produce flowers instead of vegetative structures.
• Floral organ identity genes:
  Control the development of floral organs.

Question 5

Which genes are involved in determining floral meristem identity?

Answer 5

• LEAFY (LFY):
  Expressed at the FM; required for floral meristem identity.
  Mutant lfy plants form a shoot with leaves instead of FMs and flowers.
  Overexpression of LFY converts IM to FM, producing a terminal flower.
• APETALA1 (AP1) and CAULIFLOWER (CAL):
  Transcription factors that determine floral meristem identity.
  Mutant ap1;cal plants produce IMs but no FMs, leading to a mass of IMs at the apex.

Question 6

How do regulatory interactions influence floral meristem identity?

Answer 6

TERMINAL FLOWER1 (TFL1):
- Expressed at the IM; maintains IM identity.
- LFY, AP1, and CAL suppress TFL1 to maintain FM identity.
- Loss of TFL1 converts IM to FM, producing a terminal flower.

Question 7

How are floral organs arranged in most plants?

Answer 7

• Floral organs are arranged in whorls or concentric circles within the flower.
• Each whorl produces a specific type of floral organ (e.g., sepals, petals, stamens, carpels).

Question 8

What is the ABC model in floral development?

Answer 8

• The ABC model specifies floral organ identity through the action of key transcription factors (TFs).
• A, B, and C genes produce different combinations of TFs in each whorl to determine which floral organs will be produced.
• A and C genes can regulate each other and inhibit each other’s expression, affecting the balance of floral organs.
• Reducing A gene expression leads to more stamens and fewer petals.
  Reducing C gene expression leads to more petals and fewer stamens.
• ABC genes are not sufficient alone to impose floral organ identity—additional flower-specific factors are required.

Question 9

How does the ABC(E) model extend the ABC model?

Answer 9

• E genes: Encode TFs that are involved in floral meristems and confer floral organ identity.
• The ABC(E) model includes the E genes to suppress leaf formation and promote floral organ identity in the floral meristem.
• This extension provides a complete model for floral organ identity in plants.

Question 10

How are floral organs related to leaves?

Answer 10

Floral organs are modified leaves that have adapted to perform specific functions in reproduction (e.g., petal, sepal, stamen, carpel).