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Flashcards in W11 Deck (16):

Which part of the seed embryo builds the Quiescent Centre?

It makes an anticlinal division. The top cell becomes the QC and the bottom the Columella root cap initials


What is the QC in the root meristem?

The Quiescent Centre is the organising centre of the meristem. It is surrounded by stem cells and is responsible for stopping these cells from differentiating. The suppression of differentiation leads to more division.


Which stem cells are located directly below the QC?

Columella (Wurzelhaube)


Which stem cells are located directly above the QC?

Stele initials.
Stele initials are divided into Pericycle and Procambium cells.


Which stem sells are distal to stele initials?

Endodermis/cortex initials. The daughter cells of this stem cell divide asymmetrically to produce Endodermis and Cortex cells.


Which stem cells are distal to the Endodermis/cortex stem cells?

Ectodermis initials


What does the term "Positional Information" refer to?

A local chemical field comprising of morphogens which is interpreted by the cells that are present at this location. These cells are then set on a specific differentiation path. The information which is given by this area is referred to as positional information.


Where are pluripotent and totipotent stem cells found?

Pluripotent stem cells are found in the embryo.
Totibotent stem cells are found in Blostomere.


What determines the position of the Hypophyse and therefore the Quiescent centre?

The Auxin Maximum. Auxin is pumped into the Hy by PIN. When the Hy divides horizontally, Auxin is centred in the lower cell which becomes the Columella initials. The QC has a high level of CK?


How are the endodermis and Cortex cells determined.

Positional information from the already determined endodermis and cortex cells gives the information to the younger cell to divide asymmetrically.


What are the phenotypes of Scaarecrow and short root?

Both lead to plants with short roots.
In both mutants there is no asymmetrical division of the endodermis/cortex initial.
Scarecrow: the resulting layer is a mixture of cortex and endodermis.
Short root: the resulting layer is cortex.


Where are scarecrow and short root expressed?

Scarecrow is expressed in the endodermis.
Short root is expressed in the stele (Zentralzylinder) and is transported one cell outwards into the cell nucleus of the endodermis.


How do scarecrow and short root interact?

Short root determins endodermis identity
Short root promotes scarecrow.
Scarecrow promotes periklinal division (creating the endodermis and cortex)


How do the cells in the stele and the endodermis communicate?

The communicate directly through intercellular transport of transcription factors.


What is shown with laser ablation experiments?

1. Cells are determined as endodermis/cortex cells by positional information.
-when all older cells are killed, the endodermis/cortex initial daughters no longer differentiate correctly.
Quiescent centre inhibits differentiation
-when QC killed, stem cells differentiate.
Cells can cross their compartment boundaries and take on another identity because of positional information.


What marker is used to show Auxin?

GUS with promoter gene DR5.
Problems with this is that DR5 only promotes at a certain threshold of Auxin. It also reacts to other substances. e.g. aminoacids.