leaf development Flashcards
1
Q
What are the primary roles and characteristics of leaves in plants?
A
- Leaves are the main site of photosynthesis in plants.
- They have a vascularized structure that transports water, nutrients, and photosynthetic products.
- Leaves exhibit determinate growth (they grow to a specific size).
2
Q
What are the two main types of leaves?
A
1) Simple Leaves: Single blade.
2) Compound Leaves: Made up of multiple blades (leaflets).
3
Q
What are some examples of specialized leaf adaptations in certain plants?
A
- Carnivorous plants: Leaves modified to trap and digest prey.
- Cacti: Leaves modified into spines to reduce water loss and protect against herbivory.
4
Q
Where are leaves produced in plants?
A
- Leaves are produced at the Shoot Apical Meristem (SAM).
- Leaf initiation begins with the formation of leaf primordia around the meristem.
- The youngest primordium is designated as P1, followed by I1 (next primordium).
5
Q
What is phyllotaxy, and why is it important?
A
- Phyllotaxy refers to the arrangement of leaves on the stem.
- It maximizes light capture and minimizes shading of lower leaves.
- Types of phyllotaxy patterns:
Alternate: One leaf per node at alternating angles.
Opposite: Two leaves per node across from each other.
Whorled: Three or more leaves per node forming a circle.
Spiral: Leaves develop in a spiral pattern.
6
Q
How is the production of leaf primordia regulated?
A
- Auxin is a key hormone in the initiation of leaf primordia.
- Higher concentrations of auxin trigger cell division and growth patterns.
- Older leaf primordia inhibit the emergence of new ones near them.
7
Q
What role does polar auxin transport play in leaf development?
A
- Auxin (IAA) moves in a polar, directional flow through the plant.
- PIN1 proteins: These efflux carriers create an asymmetric, polar distribution on the plasma membrane, facilitating directional transport of auxin.
- An acidic cell wall allows some auxin to move between cells as IAAH (uncharged), ensuring auxin distribution.
8
Q
How does the distribution of PIN proteins affect leaf development?
A
- PIN proteins are distributed asymmetrically in plant cells.
- Their orientation can change to redistribute auxin.
- The redistribution of auxin forms an auxin maximum, essential for initiating leaf primordium formation.
9
Q
How does auxin function as a signal in leaf development?
A
- Auxin is a critical hormone for plant growth and development.
- The polar transport of auxin creates gradients necessary for leaf primordium initiation.
- The PIN1 protein polarity helps form an auxin maximum at the site of primordium formation.
10
Q
What are the key developmental events in leaf formation?
A
- Cells in the peripheral zone of the SAM are recruited to form a leaf primordium.
- These cells acquire new identity and specialize as leaf tissue.
- The leaf acquires polarity (e.g., upper vs. lower surfaces).
- The leaf grows to its final shape and size.
- The leaf undergoes specialization for its role (e.g., photosynthesis).