Auxin Flashcards
Auxin polar transporters
- AUX1 influx carrier: contributes to the movement of IAAH into the cytoplasm. It codes for a protein similar to an amino acid permease.
- PIN1 Efflux carriers: contribute to the directional movement of auxin out of the cell via acting as a transmembrane
- The ABCB transporter: contribute to moving auxin out of the cell, regulating auxin homeostasis.
Where is AUX 1 expressed, and mutation effects
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
Where is PIN1 expressed, and mutation effects
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.
(Auxin) Antibody structure
Constant portion: distinctive of the organism that makes the ab.
Variable portion: specific to the antigen the organism recognizes as foreign.
Immunolocalization
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.
What causes the directional flow of IAA
Because different PIN proteins come into play at different places in the plant.
Physiological effects of auxin
- Cell elongation
- Phototropism
- Gravitropism
- Apical dominance
- Lateral root formation
- Fruit development
- Vascular differentiation
Cell elongation formula
Three factors control growth: turgor pressure (ψp ), yield threshold (ψ),
and irreversible extensibility of the wall (m). GR=m (ψp -ψ)
auxin affect on cell elongation
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.
Acid-growth hypothesis cycle
- auxin activates proton pumps, releasing H+ into the rh apoplast.
- The release of H+ lowers the pH.
- The acidity of the environment activates expansions.
- with looser cell walls, water can flow into the cell, causing cell wall expansion, increasing the cell size, and allowing plants to grow.
Expansins
Enzymes, when activated, loosen H-bonds between polysaccharides in the cell wall, inducing cell elongation.
Auxin as Herbicides
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.
Auxin (agent orange)
A defoliant during the Vietnam war stimulates ethylene production: leaf fall.
(Auxin) Apical dominance
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.
Auxin can trigger what in shoots?
organogenesis
Auxin levels determine what?
Phyllotaxy
GFP
Green Fluorescence protein:
unique protein that emits green color in Blue/UV light.
produced by a Jellyfish
Chromophore
required making a transgenic plant
(Auxin) Establishment of Primordia in Organogenesis
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.
Parthenocarpy
Treatment of flowers with auxin can induce fruit development without pollination or seed production.
(Auxin) Vascular differentiation
Auxin promotes vascular differentiation: new buds in the spring produce auxin that facilitates new vascularization.
Formation of new vasculature after wounding promoted by auxin.
Auxin Transport inhibitors (NPA, TIBA)
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.
Auxin involvment in tropsim
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
(Auxin) Differential growth leads to what?
Bending of the stem
Cholodny-Went theory
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.
PIN3
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.
Different tissues were recognized to have what?
Different sensitivities to auxin
How does auxin change gene expression
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.
The plasma membrane-bound auxin receptor TMK is involved with
Cell expansion, cell loosening, and other processes.
