Lecture 2 Flashcards
How do plant cells know what to develop into?
What controls plant development (general)
by co-ordinated program of cellular processes, gene expression and signalling
How do cells know where they are and what they should develop into?
They are constantly getting information from their neighbours
- each cell receives a signal that tells them what to do and where
why is positional information crucial
allows proper differentiation and morphogenesis
What is the Sussex experiment
First demonstration that cells are signalling each other
what does the top side (adaxial) of the specialize in (leaves)
light absorption
what does the botton side (abaxial) specialize in (leaves)
gas exchange
In the 1950s, what did Ian Sussex show
that a signal from the meristem is required for proper leaf polarity
What were the results of the Sussex experiment (1955)
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
What are the conclusions from the Sussex experiment
Establishment of leaf polarity
- ) signal moves out from meristem into the leaf primordium
- ) signal carries the information for adaxial development (top of leaf)
- ) the nature of the signal is not known
- ) the lower surface is the default state (signal needed to change the identity of the cell)
What are the advantages of rice plants with rolled leaves
can have more erect leaves
reduced water loss by transpiration
higher yields
true or false; meristems have defined cell layers. The cells, once formed stay in their position, so the layers are permanent
true
What are the three layers of the shoot apical meristem
L1
L2
L3
true or false; each layer in SAM undergo their own specific differentiation pathway
true
what does L1 give rise to
epidermis
what does L2 and L3 give rise to
body of the plant (including eggs and pollen)
Describe the root apical meristem RAM
- 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..)
What does the position of the cell do
determine its fate (what it will turn into)
- cells in specific rows develop in specific ways
what are the advantages of using Arabidopsis as a model plant
good for molecular genetics:
- small size
- short life cycle
- small sequenced genome
- gene transfer methods
What are transcription factors
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)
true or false; One TF can activate several other TFs- a cascade
true
true or false; TF can get a co-ordinated regulation of whole pathway
true
What does a TF look like eg. leucine zipper bound to DNA
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
What happens when KNOTTED 1 (an example of leaf formation; overexpression of TF); Tomato plants
- 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
What gene do the cells in the centre of floral buds depend on to develop into the stamens and carpels
AG transcription factor
What is the purpose of root hairs
to increase surface area for the absorption of minerals and water by the root
In Arabidopsis explain how cell to cell signalling influences adventitious root formation
root hairs will develop from epidermal cells (have GLABRA 2 gene; aka GR TF) that are next to two cortical cells
What do the mutant flowers look like (AG TF malfunction)
only have petal and sepal
- no carpel
- no stamen
- flower grows in the middle of the flower
- cannot stop growing
What are two examples of Arabidopsis transcription factors
AG TF
GLABRA 2 gene (GR TF)
