leaf development Flashcards

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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).
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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).

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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.
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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).
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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.
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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.
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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.
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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.
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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.
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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).
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