Auxin

Question 1

Auxin polar transporters

Answer 1

1. AUX1 influx carrier: contributes to the movement of IAAH into the cytoplasm. It codes for a protein similar to an amino acid permease.
2. PIN1 Efflux carriers: contribute to the directional movement of auxin out of the cell via acting as a transmembrane
3. The ABCB transporter: contribute to moving auxin out of the cell, regulating auxin homeostasis.

Question 2

Where is AUX 1 expressed, and mutation effects

Answer 2

Expressed in the subset of the columella, lateral root cap, and stele tissues, localized at the apex of protophloem cells.

aux1 mutants: dwarf, insensitive to auxin and agravitropic

Question 3

Where is PIN1 expressed, and mutation effects

Answer 3

It is detected at the basal end of auxin transport-competent cells in vascular tissue and acts as a transmembrane efflux carrier.

pin1 mutants: lessens polar auxin transport.

Question 4

(Auxin) Antibody structure

Answer 4

Constant portion: distinctive of the organism that makes the ab.

Variable portion: specific to the antigen the organism recognizes as foreign.

Question 5

Immunolocalization

Answer 5

Imaging technique: where ab is raised to the protein of interest and the second ab recognizes the constant region first. The second ab has a fluorescent tag attached, allowing localization of primary antigen in tissue.

Question 6

What causes the directional flow of IAA

Answer 6

Because different PIN proteins come into play at different places in the plant.

Question 7

Physiological effects of auxin

Answer 7

1. Cell elongation
2. Phototropism
3. Gravitropism
4. Apical dominance
5. Lateral root formation
6. Fruit development
7. Vascular differentiation

Question 8

Cell elongation formula

Answer 8

Three factors control growth: turgor pressure (ψp ), yield threshold (ψ),
and irreversible extensibility of the wall (m). GR=m (ψp -ψ)

Question 9

auxin affect on cell elongation

Answer 9

Acid growth hypothesis: Auxin rapidly increases the extensibility of the cell wall (m) via an increased rate of proton extrusion. Neutral buffers inhibit auxin-induced growth, and compounds that acidify the wall increase growth.

Question 10

Acid-growth hypothesis cycle

Answer 10

1. auxin activates proton pumps, releasing H+ into the rh apoplast.
2. The release of H+ lowers the pH.
3. The acidity of the environment activates expansions.
4. with looser cell walls, water can flow into the cell, causing cell wall expansion, increasing the cell size, and allowing plants to grow.

Question 11

Expansins

Answer 11

Enzymes, when activated, loosen H-bonds between polysaccharides in the cell wall, inducing cell elongation.

Question 12

Auxin as Herbicides

Answer 12

Synthetic auxins, which are dicot herbicides, work by causing uncontrolled cell division in vascular tissue via an abnormal increase in cell wall plasticity, protein biosynthesis, and ethylene production.

Disruption of metabolism, ion channels, and more.

Question 13

Auxin (agent orange)

Answer 13

A defoliant during the Vietnam war stimulates ethylene production: leaf fall.

Question 14

(Auxin) Apical dominance

Answer 14

The presence of the growing apical bud inhibits the growth of the lateral buds. A balance between auxin, cytokinin (coming up from the roots), and ABA (dormant lateral buds) maintains the inhibition.

Question 15

Auxin can trigger what in shoots?

Answer 15

organogenesis

Question 16

Auxin levels determine what?

Answer 16

Phyllotaxy

Question 17

GFP

Answer 17

Green Fluorescence protein:

unique protein that emits green color in Blue/UV light.

produced by a Jellyfish

Chromophore

required making a transgenic plant

Question 18

(Auxin) Establishment of Primordia in Organogenesis

Answer 18

Auxin is continuously transported to the SAM and controls the position at which cells are recruited into organogenesis. High auxin in meristem region = primordia emergence.

Once established, it functions as a sink for auxin depleting auxin in the surrounding cells.

Question 19

Parthenocarpy

Answer 19

Treatment of flowers with auxin can induce fruit development without pollination or seed production.

Question 20

(Auxin) Vascular differentiation

Answer 20

Auxin promotes vascular differentiation: new buds in the spring produce auxin that facilitates new vascularization.

Formation of new vasculature after wounding promoted by auxin.

Question 21

Auxin Transport inhibitors (NPA, TIBA)

Answer 21

The role of auxin in vascular development can be determined using these transporter inhibitors.
Mutants in auxin transport cause vascular development similar to auxin transport inhibitors.

Question 22

Auxin involvment in tropsim

Answer 22

Tropic response - response to a directional stimulus

Phototropism - light response mediated by lateral redistribution of auxin.
Gravitropism - gravity response correlates with cholodyn-went model.

positive phototropism - grows toward the light
positive gravitropism - grows toward the center of the earth

Question 23

(Auxin) Differential growth leads to what?

Answer 23

Bending of the stem

Question 24

Cholodny-Went theory

Answer 24

Phototropic stimulus results in unequal lateral distribution of
auxin at the coleoptile tip. Polar transport redistributes this auxin to the growth zone and gets
differential growth and curvature.

Question 25

PIN3

Answer 25

Changes polarity in response to a change in the gravity vector. responsible for the
lateral reorientation of
auxin during shoot and root
phototropism and
gravitropism.

Question 26

Different tissues were recognized to have what?

Answer 26

Different sensitivities to auxin

Question 27

How does auxin change gene expression

Answer 27

Auxin receptor – TIR1
An F-box protein that is part
of a larger protein complex
that facilitates protein
degradation.
Auxin binding to TIR1
activates and causes
ubiquitination and proteolytic
degradation of AUX/IAA
transcriptional repressors.
Auxin acts as a “molecular
glue” to hold the AUX/IAA
repressors in place.

Question 28

The plasma membrane-bound auxin receptor TMK is involved with

Answer 28

Cell expansion, cell loosening, and other processes.