Lecture 2

Question 1

What controls plant development (general)

Answer 1

by co-ordinated program of cellular processes, gene expression and signalling

Question 2

How do cells know where they are and what they should develop into?

Answer 2

They are constantly getting information from their neighbours
- each cell receives a signal that tells them what to do and where

Question 3

why is positional information crucial

Answer 3

allows proper differentiation and morphogenesis

Question 4

What is the Sussex experiment

Answer 4

First demonstration that cells are signalling each other

Question 5

what does the top side (adaxial) of the specialize in (leaves)

Answer 5

light absorption

Question 6

what does the botton side (abaxial) specialize in (leaves)

Answer 6

gas exchange

Question 7

In the 1950s, what did Ian Sussex show

Answer 7

that a signal from the meristem is required for proper leaf polarity

Question 8

What were the results of the Sussex experiment (1955)

Answer 8

1955 Sussex - incision in meristem
- leaves on that side developed asymmetrically
- instead of top; a bottom formed
- rounded
- no waxy cuticle 
- no pallisade cells
- stomata all round
 over all the asymmetry of the plant is lost 
(both surfaces are abaxial)

ONCE MERISTEM IS CUT, SIGNAL IS LOST

Question 9

What are the conclusions from the Sussex experiment

Answer 9

Establishment of leaf polarity

1. ) signal moves out from meristem into the leaf primordium
2. ) signal carries the information for adaxial development (top of leaf)
3. ) the nature of the signal is not known
4. ) the lower surface is the default state (signal needed to change the identity of the cell)

Question 10

What are the advantages of rice plants with rolled leaves

Answer 10

can have more erect leaves
reduced water loss by transpiration
higher yields

Question 11

true or false; meristems have defined cell layers. The cells, once formed stay in their position, so the layers are permanent

Answer 11

true

Question 12

What are the three layers of the shoot apical meristem

Answer 12

L1
L2
L3

Question 13

true or false; each layer in SAM undergo their own specific differentiation pathway

Answer 13

true

Question 14

what does L1 give rise to

Answer 14

epidermis

Question 15

what does L2 and L3 give rise to

Answer 15

body of the plant (including eggs and pollen)

Question 16

Describe the root apical meristem RAM

Answer 16

• cells are in rows
• each row of cells differentiates along a defined pathway to become a particular class of cell
  (epidermis, cortex, endodermis, pericycle, etc..)

Question 17

What does the position of the cell do

Answer 17

determine its fate (what it will turn into)

- cells in specific rows develop in specific ways

Question 18

what are the advantages of using Arabidopsis as a model plant

Answer 18

good for molecular genetics:

• small size
• short life cycle
• small sequenced genome
• gene transfer methods

Question 19

What are transcription factors

Answer 19

control development:

• TF’s are proteins that bind to DNA regulatory sequences(promoters) upstream of genes
• the binding can activate or repress production of mRNA from gene (can stimulate or inhibit RNA pol 2)

Question 20

true or false; One TF can activate several other TFs- a cascade

Answer 20

true

Question 21

true or false; TF can get a co-ordinated regulation of whole pathway

Answer 21

true

Question 22

What does a TF look like eg. leucine zipper bound to DNA

Answer 22

modular proteins

• 2 large alpha helices
• Dimerisation and DNA binding domain interact to form coiled coil to hold helices together
• insert into major groove of DNA

Question 23

What happens when KNOTTED 1 (an example of leaf formation; overexpression of TF); Tomato plants

Answer 23

• knotted 1 is a homeotic gene involved in leaf and leaflet formation
• its overexpression in tomato plants results in leaves that are SUPER COMPOUND in comparison to normal leaves

Question 24

What gene do the cells in the centre of floral buds depend on to develop into the stamens and carpels

Answer 24

AG transcription factor

Question 25

What is the purpose of root hairs

Answer 25

to increase surface area for the absorption of minerals and water by the root

Question 26

In Arabidopsis explain how cell to cell signalling influences adventitious root formation

Answer 26

root hairs will develop from epidermal cells (have GLABRA 2 gene; aka GR TF) that are next to two cortical cells

Question 27

What do the mutant flowers look like (AG TF malfunction)

Answer 27

only have petal and sepal

• no carpel
• no stamen
• flower grows in the middle of the flower
• cannot stop growing

Question 28

What are two examples of Arabidopsis transcription factors

Answer 28

AG TF

GLABRA 2 gene (GR TF)