8. Phototropism, Auxin & Microtubule Dynamics

Question 1

Which experiments performed Darwin already 1880?

Answer 1

intact seed: curvature to light
cut cap: no curvature
cap on seed: no curvature

Question 2

What is a coleoptil?

Answer 2

Schutzorgan für das aufgehende erste Blatt

Question 3

Which experiments did Wendt around 1926?

Answer 3

1. Put Coleoptil tips on gelatin
2. discarded tips and cut gelatin in smaller blocks
3. each gelantine placed on one side of coleoptil stump (nicht direkt drauf sondern versetzt)
4. Coleoptil bends in total darkness –> one can measure the angle of the coleoptil

Question 4

At which blue light wave length oat coleoptiles have the most curvature per photon?

Answer 4

440 nm

Question 5

What happens on molecular level if plant switches from light into darkness?

Answer 5

FMN - Flavinadeninmonenucleotide changes their conformation.
LOV domain sturcture 390 (wicht SH and CYS) binds to FMN (just S, not SH)
reaction is reversible and goes back during darkness

Question 6

What is an apoprotein?

Answer 6

Part of a protein which consists just of amino acids + postetisch group = functional protein

Question 7

What are phototropins?

Answer 7

Lichtrezeptoren (FMN an denen LOV bindet)

Question 8

What is a LOV domain and how does it work?

Answer 8

LOV-Domänen (light, oxygen or voltage) bind flavine mononucleotide. The N-terminal domain undergoes phosphorylation upon blue light irradiation. Subsequently downstream protein substrates are phosphorylated
(requires further characterization).

Question 9

What induces unilateral light (von nur einer Seite)? How can you investigate that?

Answer 9

Unilateral light induces a lateral redistribution of auxin during the phototropism of Arabidopsis thaliana seedlings

An auxin-sensiIve promoter element (DR5 an ARF
DNA-binding sequence) generates expression of the enzyme β-glucuronidase (GUS), which converts a substrate to a blue product

Question 10

Where is the PIN 3 carrier distributed and what does it contributes to?

Answer 10

The PIN3 auxin efflux carrier contributes to phototropism and can be located at the lateral membranes of the starch sheath/endodermis, and pericycle cells.
PIN3-GFP polarises laterally, away from the light on the light-facing side of the hypocotyl endodermis
GNOM and PINOID have opposite effects on PIN3 localization

Question 11

What does Auxin induces in the corn (Zea mays) coleoptile?

Answer 11

Auxin induces transverse microtubule orientation in the corn (Zea mays) coleoptile
Microtubules in the oat (Avena sativa) coleoptile are oriented transversely at the light-facing side and longitudinally at the light-remote side

Question 12

What induces reorientation in microtubules in Arabidopsis thaliana hypocotyl (Keimstängel)?

Answer 12

Blue light

Question 13

What can KATANIN1 (KTN1) do? (and also kantenin in general)

Answer 13

KTN1 can induce the shrinkage of transverse microtubules at crossing points
KTN1 activity is required for reorientation from transversal to longitudinal
KTN1 activity is required for blue light-dependent phototropism
Katanin activity of microtubule separation and reinitiation can be compared to the function of a railway turntable
Many animal cells also show an alignment of microtubule patterns, which does not arise from the centrosome (i.e. acentrosomal), and katanin may play an important role here as well.

Question 14

What is phototropin activity good for?

Answer 14

Phototropin activity (PHOT1 and PHOT2) is primarily required for microtubule orientation from transverse to longitudinal