Lecture 9

Question 1

How does secondary growth in roots occur?

Answer 1

When residual procambium in the xylem and phloem become meristematic (reactive and begin dividing) the pericycle opposite the xylem also begins dividing

Question 2

What happens to the two types of pericycle during secondary growth in roots? (Aka. What do they form?)

Answer 2

The meristematic pericycle/residual procambium form a continuous ring around the xylem to form the root vascular cambium while the remaining pericycle forms the first cork cambium

Question 3

Strategies for controlling plant development (3)

Answer 3

Regulate cell division (rate/direction/polarity of division)

Cell expansion (direction/length/uniformity of expansion)

Cell differentiation and specialization (positive/negative regulation, cell specialization during maturation)

Question 4

Cell cycling occurs in specific plant zones. Explain where they are found (location/timing) in monocots and eudicots.

Answer 4

Monocots: cell division zones are localized (RAM at bottom tip, SAM at dome)

Eudicots: cell division zones move from taking up the entire cell when introduced to negligent when mature (cycle through proliferation -> expansion -> maturation)

Question 5

Vascular differentiation in eudicots fills in the lead with veins by what mechanism?

Answer 5

Form a central vein from base to top then fill in spaces with minor veins from tip to base

Question 6

When is photosynthetic physiology established?

Answer 6

At the end of cell division, shortly after cells have all matured

(Initially decline due to nutrient deprivation in competition with younger leaves)

Question 7

Leaf senescence pathway (3)

Answer 7

Age/hormones/stresses -> signal transduction -> transcription factors

Question 8

Transcription factors associated with inhibiting/promoting lead senescence (2)

Answer 8

SDG: inhibit senescence by down-regulating senescence genes (photosynthetic genes)

SAG: a senescence-associated gene that promotes senescence (proteases, nucleases, lipases)

Question 9

SAG’s promote what (2)

Answer 9

Degradation
Nutrient recycling (retrieving nutrients from the old leaf and transmitting them to young leaves (cannibalizes old))

Question 10

Layers of leaf that form during senescence (2)

Answer 10

Separation layer (where cell wall breaks down)
Protective layer (protects leaf from bacterial penetration)

Question 11

The cell cycle (2 sections, 3 phases, 2 checkpoints)

Answer 11

2 sections: interphase, mitosis and cytokinesis
3 phases (in interphase):
- G1 (synthesis of cytoplasm + components)
- S (DNA synthesis)
- G2 (prep for mitosis, nuclear migration, cytoskeletal formation)
2 checkpoints: G1 -> S, G2-> M

Question 12

Purpose of checkpoints

Answer 12

To ensure the previous phase was carried out accurately

Question 13

What are CDKs?

CDKs are regulated by (3)? Cyclin is regulated by (2)? When activated both imitate which cell cycle phase?

Answer 13

CDKs are protein kinases that phosphorylate proteins using ATP to control their function/the downstream pathway

CDKs regulated by: cyclin, phosphorylationC dephosphorylation
Cyclin regulated by: synthesis, degradation

Activated-CDKs initiate mitotic division
Activated-cyclin initiates S phase

Question 14

What is a cytoskeleton and what does it compose of (3)?

Answer 14

A dynamic network of protein filaments within the cytosol

Composed of: microtubules, actin filaments, intermediary filaments

Question 15

Cytoskeleton function (6)

Answer 15

Moves/positions organelles
Positions protein complexes on organelles/plasmalemma
Moves vesicles to plasma membrane (during exocytosis)
Drives cell division
Orientation of cell expansion/differentiation
Positions wall divers (for a normal cell)

Question 16

Cytoskeleton during mitosis/cytokinesis

Answer 16

Mitosis: cortical microtubules -> preprophase band -> mitotic spindle -> phragmoplast

Cytokinesis: cell plate forms between microtubules -> -> microtubules realign to original position

Question 17

Cytoskeleton and mitotic spindle initiation process of pulling apart

Answer 17

Spindle fibres attach to protein complexes to make kinetochores that bind to the sides of the chromatid OR send a signal to inhibit anaphase

When all kinetochores are attached an inhibitory signal is activated, APC (prevents metaphase -> anaphase) is activated and ubiquitin is coupled to cyclin

Cyclin degrades and motors pulling chromatids are activated

Question 18

Actin/microtubule placement essential for (5)

Answer 18

Correct cell plate positioning
Control of directional cell expansion
Single cell morphogenesis 
Cell differentiation 
Cell-to-cell communication

Question 19

Stomatal development pathway (4)

Answer 19

Postprotodermal cell -> meristemoid mother cell -> meristemoid -> guard cell

Question 20

What is the point of inhibitory proteins in stomatal development?

Answer 20

Induce negative regulation that establishes the placement of guard cells so that they are not too close to one another (form a basipetal pattern)

Question 21

Role of CDKs in stomatal development

Answer 21

Regulation of CDKs is crucial

If reduce activity of B1-type CDKs

• fail to undergo the final guard cell division (abnormal cells blocked in G2 phase)
• have a decrease in stomatal density (meristemoid division is blocked; satellite meristemoid formation is inhibited) t

Question 22

Mechanisms of cell expansion (3)

Answer 22

Cell wall loosening
Water uptake
Generation of a new wall

Question 23

Patterns of expansion (4)

Answer 23

Non-polar growth
Polar growth
Localized (tip) growth
Regulation of growth direction

Question 24

Role of microtubules and actin filaments in directional growth

Answer 24

Microtubules: align perpendicular to expansion and control placement of cellulose during expansion

Actin filaments: don’t have a specific alignment; move Golgi-produced vesicles to cell periphery

Question 25

What happens to an expanding cell treated with tubulin inhibitors?

Answer 25

Leads to non-directional cell expansion making blobs

Question 26

What controls the orientation of cellulose microfibrils?

Answer 26

The positioning of microtubules in the outer cytoplasm

Question 27

Patterns of expansion (3)

Answer 27

Non-polar growth (isotropic: even in all directions)

Polar growth (ansiotropic: uneven growth in one direction)

Localized (tip) growth (transverse microfibrils/cortical fibres have polar growth, randomly oriented microfibrils) (make Root hair)

Question 28

When does trichome elongation occur? Stopped?

Arrangement of microtubules throughout trichome elongation (2)

Answer 28

Elongation occurs during interphase
Cells are stopped in the G1 phase

Arrangement:
- cortical microtubules align perpendicularly
> cellulose microfibrils follow accordingly
> elongation and secondary cell wall synthesis occur
- microtubules align in a steeply pitched manner

Question 29

What are cotton fibres made of? Mechanisms of cotton boll formation (2)

Answer 29

Made of elongated trichomes from the seed coat

Mechanisms:
Cell wall loosening (increase expansin mRNA levels)
Uptake of water following surge of osmotically active solutes (provide turgor for expansion)

Question 30

Mechanism of water uptake induced by osmotica (7)

What is this process called?

Answer 30

Trichomes become symplastically isolated
Callose is deposited into the plasmalemma to intensify the osmotic potential and pressure potential difference
Osmotica accumulates in symplast
Water potential decreases
Water flows in
Generates turgor pressure
Cell expands

Process is called: Plasmodesmatal Gating

Question 31

Turgor driven processes in plants (7)

Answer 31

Stomatal opening (PD occluded at maturity)

Cell expansion during growth (temporary PD occlusion)

Leaf movement (uncertain)

Root pressure (uncertain)

Phloem transport (PD occlusion in apoplast loaders/PD size limited in symplast loaders)

Tropisms (PD occlusion by callose localize expansion)