FRST 200 Primary Growth in Plants (Week 5 & 6)

Identify the three zones of primary growth within the root?

1. Zone of Cell Division

Location: Apical meristem, just behind the root cap

Function: Rapid mitosis producing new root cells

Contains initials that give rise to primary meristems

2. Zone of Cell Elongation

- Cells increase in length

- Responsible for root extension into soil

- Pushes the root tip forward

3. Zone of Cell Differentiation (Maturation)

- Cells specialize into epidermis, cortex, xylem, phloem, etc.

- Root hairs develop here

-Tissues become fully functional

What are the different tissue functions in the roots and shoots?

1:

a. Epidermis-

Outermost tissue layer

Protects the plant surface

In roots: absorbs water and minerals (root hairs)

In shoots/leaves: reduces water loss (cuticle, stomata)

b. Endodermis-

Controls which substances reaches the plant's core tissues, accomplished by the casparian strip, prevents backflow of water + dissolved nutrients, stores food, protects against pathogens

Xylem- transports water + minerals

Phloem- transports sugars + hormones + lipids

Cortex- structural support, flexibility, storage

Pericycle- facilitates nutrient transport, forms vascular cambium and cork cambium

What are the 3 primary meristems?

procambium, ground meristem, protoderm

Which root tissues arise from the three primary meristems (procambium, ground meristem, protoderm)?

Procambium- primary xylem, primary phloem, pericycle

Ground meristem- cortex, endodermis

Protoderm- epidermis

Difference between large and fine roots?

Large roots (support and transport)

- Provide anchorage and stability

- Transport water + minerals from fine roots to the stem

- Storage for starch and sugar

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Fine Roots (resource acquisition)

- Absorb water and nutrients from the soil

- Primary site of mycorrhizal associations

What's the difference monocot vs dictot

monocot:

- 1 cotyledon

- fibrous roots

- petals in multiples of roots

- parallel venation

- scattered

dicot:

- 2 cotyledon

- tap roots

- have 4 or 5 petals

- palmate venation

- ringed

Phytomer?

A phytomer is the basic repeating structural unit of a shoot.

- Position of leaf primordia formed at the shoot apical meristem (SAM)

- Auxin distribution in the SAM- areas with more of it decide exactly where a new leaf will form

How is axillary bud growth controlled?

Apical dominance- the process where axillary buds are kept dormant by the SAM

Achieved through auxin; SAM produces auxin which inhibits bud growth

What happens if the main SAM is lost?

If the SAM is removed (a technique) the auxin supply drops dramatically, apical dominance is released and one or more auxiliary buds begin to grow into lateral branches

2 types of veins in a leaf?

Major veins= long distance transport, xylem brings water and minerals into the leaf, phloem exports sugars out of the leaf (parallel in monocot, net like, branching)

Minor veins= short distance transport, collect sugars from photosynthetic cells, delivers water directly to mesophyll cells, increase efficiency of photosyntheis

Evergreen vs deciduous leaves?

Evergreen=

Long lived

Small, thick, tough

High leaf mass/ area

Thick cuticle

Low photosynthetic rate

More resistant to cold, drought

Slow nutrient cycling

Deciduous =

Short lived (shed annually)

large, thin, soft

Low leaf mass/ area

Thin cuticle

Higher photosyntehtic rate

Less resistant to cold, drought

Fast nutrient cycling

2 structural adaptations observed in leaves of hydrophytes, xerophytes, and mesophytes

Hydrophyte- epidermis modified to be thin/ none at all

-> allowing gas exchange

Mesophyte-

Xerophyte- epidermis modified to have a thick, waxy cuticle to prevent water loss, efficient gas exchange, and reflects heat from intense sunlight

Explain how and why trees may increase stem growth to avoid shade / neighbour competition?

When neighbouring plants shade them, the red:far-red (R:FR) light ratio decreases because leaves absorb red light and reflect far-red light.

Trees use phytochrome photoreceptors in leaves and shoots.

Phytochromes detect changes in red vs far-red light.

Low R:FR shifts phytochrome into its inactive form, triggering a shade-avoidance response.

Trees use phytochrome photoreceptors in leaves and shoots.

Phytochromes detect changes in red vs far-red light.

Low R:FR shifts phytochrome into its inactive form, triggering a shade-avoidance response.

Importance of phytochrome?

- Promotes photosynthesis, lower wavelength=more effective

- Neighbouring trees absorb red light and reflect far red light

- When u change the ratio from red to far red, it deactivates phytochrome

-Red light activates phytochrome but far red light doesn't

What's the importance of red light?

-Promotes photosynthesis, lower wavelength=more effective

-Neighbouring trees absorb red light and reflect far red light

-When u change the ratio from red to far red, it deactivates phytochrome

-Red light activates phytochrome but far red light doesn't