Plant Cell Biology

Question 1

How are plant cells different from animal cells?

Answer 1

• cell wall
• chloroplast (where photosynthesis occurs)
• vacuole

Question 2

Why are cell walls important?

Answer 2

• protection
• strops the cell from bursting from high pressure (hydrostatic pressure developing inside the cell)
• “skeleton” of the plant, lets it stand up right

Question 3

What is a plant cell without a cell wall called?

Answer 3

Protoplast

Question 4

What forms the plant cell wall?

Answer 4

• cellulose microfibrils
• cross-linked together by proteins
• alignment of microfibrils

Question 5

What determines the direction of growth and cell shape of a plant cell?

Answer 5

The alignment of microfibrils
- anisotropic growth (directionally dependent)
- Growth will occur in the opposite direction of the microfibril
○ Pulls the microfibril apart
○ Grows perpendicularly
○ Break & loosen bonds for stretching to take place (elongation needs to be control in a certain direction)
- Without alignment of microfibrils = cells with no shape

Question 6

How does the cell wall change during growth?

Answer 6

1. bonds between cellulose fibrils must be loosened or broken
2. more water can enter the vacuole
3. new fibrils are laid down in the gaps
   - stretching occurs in the opposite direction to the cellulose

Question 7

How is plant cell growth controlled?

Answer 7

cellulose synthase puts the microfibrils where it is

• cell growth is dependent on microtubule alignment because disruption of the microtubules pertrubs cell shape
• dependent on alignment of cellulose microfibrils

Question 8

What experiment was conducted to see how plant cell growth is controlled?

Answer 8

1. stain tubulin to see where the microtubules are
   - are micro tubulins responsible?
2. Interrupt the microtubules from doing their job with Oryzalin
3. Insert plant Arabidopsis (looking at the Arabidopsis roots)
4. Get rid of Cell Wall
5. Stain
6. Look at the hairs/ shape
   - cellulose loses the shape so hair has lost shape
7. Stabilise the microtubules (see what happens in the cellulose)
   - control = triangle shape seen
   - with paclitaxel = spherical shape

Question 9

What does Oryzalin do to microtubules?

Answer 9

Depolymerises

Question 10

What does Paclitaxel do to microtubules?

Answer 10

Stabilises microtubules, preventing their depolymerisation

Question 11

What experiment can be conducted to see the relationship between alignment of microtubules and cellulose microfibrils?

Answer 11

• add tag to cellulose synthase (enzyme that makes cellulose) and then stain
• can then look at microtubules and cellulose synthesis at the same time
• merging of images, the microtubule alignment and cellulose synthase alignment are similar/ the same
• therefore microtubule is directing the cellulose synthase

Question 12

What is the hypothesis with how cellulose microfibrils are orientated in the cell wall?

Answer 12

• cellulose synthase enzyme runs along the track laid out by the microtubule
• creates cellulose along the way

Question 13

What is MOR1?

Answer 13

a protein that binds to and organises MTs

Question 14

How is the mor1 mutant temp sensitive?

Answer 14

At different temperatures, the microtubules are orientated differently

• at 21 degrees, functions normal, all nicely organised
• > 21 degrees, microtubule organisation is completely different

Question 15

What is the contradictory evidence against the model of the cellulose microfibrils in the cell wall?

Answer 15

• not all microtubules are formed parallel to cell wall fibrils
• cellulose synthase mutants with very little un-orientated cellulose still have orientated microtubules

Question 16

What do CMU proteins do?

Answer 16

Steadies the cellulose synthase so it doesn’t twist..

Question 17

What changes can plant hormones introduce?

Answer 17

• Gibberlin/ Gibberllic acid can reverse microfibril/ cellulose direction (cell elongation)
• Lodging, hormone applications can stop cell elongation as lodging occurs killing seeds