Lecture 17 - Meristem development Flashcards
What is the shoot apical meristem (SAM)?
A region in the growing shoot containing meristematic cells
What are the three parts of a shoot apical meristem? [3]
- Leaf primordium
- Apical meristem
- Lateral branch bud
What are the two parts of a apical meristem? [2]
- Central zone
- Peripheral zone
How are the cells arranged in the apical meristem?
- Tunica (L1 and L2)
- Corpus (L3)
- Initial cells (stem cell organiser)
What happens to a shootmeristemless1 (STM1) mutant?
The shoot apical meristem is not formed
Where is shootmeristemless1 expressed?
In the shoot apical meristem
What happens during over expression of shootmeristemless1?
There are too many shot apical meristems being formed
What is the role of WUSCHEL in the meristem?
- Expressed in meristem initial cells -
- Helps meristems to form
What is the role of clavata in the meristem?
Maintaining the meristem
Where are STM and WUS expressed?
In the central zone
Where is Clavata1, 3 expressed?
In the peripheral zone
What is phyllotaxy?
The arrangement of leaves
What are the ways leaves can be arranged along a stem? [6]
- Alternate
- Opposite
- Whorled
- Distichous (180’)
- Descussate (90’)
- Spiral
How is phyllotaxy determined?
- Inhibitory field hypothesis
- Biophysical hypothesis
- General control of genes
What are two common features for the development of leaf primordia?
- 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
What is the Inhibitory field hypothesis?
Signals from the emerging leaf primordium inhibits the formation of new new leaf primordium in the neighbouring area
How can the formation of Primordia be induced?
Expansins loosen the cell wall so primordia can form there
What happens to Auxin at low pH?
- It is protonated
- Can move through the plasma membrane
What happens to Auxin at a higher pH?
- Loses the proton
- Can no longer move through the plasma membrane
How is the charged auxin moved through the plasma membrane?
- Through PIN1
- An auxin efflux carrier
What does NPA do?
- It is a auxin transporter inhibitor
- Inhibits leaf primordium formation
What happens to a PIN1 mutant?
They can not form leaf primordia
How is auxin moved within a shoot apical meristem?
It is moved towards a centre site
Where is the auxin concentration at its highest?
Right where primordium will form
How does PIN1 distribution change after primordium initiation?
Changes to direct auxin flow into developing midvein
How does Cytokinin contribute to phyllotaxy patterning?
Sets up inhibitory fields to provide robustness in the meristem
