VL 38 (Markus Grebe)

Question 1

What is Cell Polarity?

Answer 1

A persistent asymmetrical, distribution of structures (or molecules) along an axis

Question 2

Some cues for cell and tissue polarity in plants

Answer 2

Exogenous factors
- light direction and quality
- gravity
- sperm entry (some algae)

Endogenous factors
- directionally transported hormones e.g. auxin
- other genetically determined intrinsic cues like small signalling peptides

Question 3

The Asymmetric Division of the Arabidopsis thaliana Zygote

Answer 3

is defect in mutants (gnom)

–> Early Defects in Cell Polarity and Asymmetric Zygote Division Are Accompanied by Defective Organ Polarity in Seedlings

–> GNOM Is Required for Coordinate Polar Positioning of the PIN-FORMED1 (PIN1) Auxin Efflux Carrier in the Embryo

–> GNOM Encodes for an ARF GEF, a Guanine-Nucleotide-Exchange Factor (GEF) for Small GTP-binding Proteins of the ARF1 Family

Question 4

The Vesicle Trafficking Inhibitor Brefeldin A (BFA) Reversibly Inhibits Polar PIN1 Protein Recycling from/to the Basal Membrane

Answer 4

–> GNOM is a Direct Target for BFA and Mediates Polar PIN1 Recycling Between Plasma Membrane and Endosomes

Question 5

A Model for PIN-Dependent Polar Auxin Transport in the Early Arabidopsis Embryo

Answer 5

–> PIN Polarity Is First Established Directly After Cell Division

Question 6

Cell Polarity, Planar Polarity, Tissue Polarity, Organ Polarity

Answer 6

planar polarity specific tissue polarity involving coordinate asymmetrical distribution of cells and subcellular structures within the plane of a single cell layer
–> In Animals and in Plants

tissue polarity coordinate asymmetrical and ordered distribution of cells and subcellular structures within a tissue

organ polarity asymmetrical and ordered distribution of cell and tissue
layers along an axis of an organ

Question 7

Planar Polarity in the Drosophila Wing