Lecture 17 - Meristem development

Question 1

What is the shoot apical meristem (SAM)?

Answer 1

A region in the growing shoot containing meristematic cells

Question 2

What are the three parts of a shoot apical meristem? [3]

Answer 2

• Leaf primordium
• Apical meristem
• Lateral branch bud

Question 3

What are the two parts of a apical meristem? [2]

Answer 3

• Central zone

- Peripheral zone

Question 4

How are the cells arranged in the apical meristem?

Answer 4

• Tunica (L1 and L2)
• Corpus (L3)
• Initial cells (stem cell organiser)

Question 5

What happens to a shootmeristemless1 (STM1) mutant?

Answer 5

The shoot apical meristem is not formed

Question 6

Where is shootmeristemless1 expressed?

Answer 6

In the shoot apical meristem

Question 7

What happens during over expression of shootmeristemless1?

Answer 7

There are too many shot apical meristems being formed

Question 8

What is the role of WUSCHEL in the meristem?

Answer 8

• Expressed in meristem initial cells -

- Helps meristems to form

Question 9

What is the role of clavata in the meristem?

Answer 9

Maintaining the meristem

Question 10

Where are STM and WUS expressed?

Answer 10

In the central zone

Question 11

Where is Clavata1, 3 expressed?

Answer 11

In the peripheral zone

Question 12

What is phyllotaxy?

Answer 12

The arrangement of leaves

Question 13

What are the ways leaves can be arranged along a stem? [6]

Answer 13

• Alternate
• Opposite
• Whorled
• Distichous (180’)
• Descussate (90’)
• Spiral

Question 14

How is phyllotaxy determined?

Answer 14

• Inhibitory field hypothesis
• Biophysical hypothesis
• General control of genes

Question 15

What are two common features for the development of leaf primordia?

Answer 15

• The position of the existing primordia are important for the position of the new primordia
• Pre-existing primordia inhibit new primordium formation in adjacent area

Question 16

What is the Inhibitory field hypothesis?

Answer 16

Signals from the emerging leaf primordium inhibits the formation of new new leaf primordium in the neighbouring area

Question 17

How can the formation of Primordia be induced?

Answer 17

Expansins loosen the cell wall so primordia can form there

Question 18

What happens to Auxin at low pH?

Answer 18

• It is protonated

- Can move through the plasma membrane

Question 19

What happens to Auxin at a higher pH?

Answer 19

• Loses the proton

- Can no longer move through the plasma membrane

Question 20

How is the charged auxin moved through the plasma membrane?

Answer 20

• Through PIN1

- An auxin efflux carrier

Question 21

What does NPA do?

Answer 21

• It is a auxin transporter inhibitor

- Inhibits leaf primordium formation

Question 22

What happens to a PIN1 mutant?

Answer 22

They can not form leaf primordia

Question 23

How is auxin moved within a shoot apical meristem?

Answer 23

It is moved towards a centre site

Question 24

Where is the auxin concentration at its highest?

Answer 24

Right where primordium will form

Question 25

How does PIN1 distribution change after primordium initiation?

Answer 25

Changes to direct auxin flow into developing midvein

Question 26

How does Cytokinin contribute to phyllotaxy patterning?

Answer 26

Sets up inhibitory fields to provide robustness in the meristem