Lecture 2: Plant Propagation (9/1)

Do layers L1, L2, and L3 layers divide in one or all planes?

L1: one plane (anticlinal)

L2: one plane (anticlinal)

L3: all planes (sectorial)

What are the L1 and L2 layers called, and the L3 layer?

L1 + L2: tunica

L3: corpus

Periclinal chimera: layer, spatial distribution, vegetative stability

Layer: one layer (L1, L2, or L3)

Spatial distribution: top of shoot apex

Vegetative stability: relatively stable, most common chimera in horticulture

Mericlinal chimera: layer, spatial distribution, vegetative stability

Layer: one layer

Spatial distribution: side of shoot apex

Vegetative stability: unstable

Sectorial chimera: layer, spatial distribution, vegetative stability

Layer: multiple

Spatial distribution: top of shoot apex

Vegetative stability: unstable

What does the L1 layer give rise to?

The colorless epidermis

What does the L2 layer give rise to?

Sub-epidermal palisade mesophyll and abaxial spongy mesophyll cells. Also produces pollen cells

What does the L3 layer give rise to?

Upper and middle layers of spongy mesophyll. Does not contribute to leaf margins

Invasion

When a mutation on one layer of the apical meristem moves into another layer

What do L1:L2:L3 look like on plants?

Mutations on the L1 don’t have much of a difference

Mutations on L2 affect leaf margins

Mutations on L3 affect the center of the leaf

How do you know whether something is a periclinal chimera?

Uniform pale margin all the way around the leaf (L2 mutant)

Solid pale center/midrib with green margins (L3 mutant)

Every node produces the same patterned foliage. Stable indefinitely through stem cuttings.

How do you know whether something is a mericlinal chimera?

Only one half or edge of the leaf exhibits the variegation/mutation.

How do you know whether something is a sectorial chimera?

An entire vertical segment of the stem, leaf, flower, or fruit is completely replaced by the mutant tissue

Typically short-lived

Where are the central zone, peripheral zone, and rib zone on a meristem?

Why are stock plants kept to juvenile growth?

Because juvenile tissue typically forms adventitious roots more easily

What area of a plant is distal vs. proximal? How does this relate to polarity in rooting?

Proximal is near the middle of the plant while distal is toward either side (root/shoot)

Cuttings form roots at the proximal side

Canal theory

The flow of auxin through cells of high auxin content (source) towards cells of low auxin content (sink) polarizes and upregulates auxin transport . This leads to channeling/ canalization of auxin through files of cells

Auxin (roles)

Elongation and bending

Apical dominance and apical meristem development

Vascular differentiation and root formation

Fruit development

Gibberellins (roles)

Seed germination, flowering, pollen and fruit development, dormancy

Antagonistic towards ABA

Cytokinins (roles)

Cell division, delaying leaf senescence, breaking apical dominance, breaking dormancy

Ethylene (roles)

Ripening, senescence and abscission, breaking seed dormancy, promoting flowering (in some species), stress responses

Abscisic acid (roles)

Promotes senescence, induces dormancy, stomatal closure

Antagonistic towards GA

What is callus made up of?

Unorganized mass of parenchyma cells

What is the difference between periclinal and mericlinal chimeras?

A periclinal chimera covers the entirety of the apex, while a mericlinal chimera only covers part of it