- First plant hormone discovered was auxin.
- By Frits Went
- The chemical itself was first isolated from urine, it is indole acetic acid
- Auxin a- C18 H33 O5 & Auxin b C18 H30O4 (IAA) exist in plants
Naturally occurring auxins
- IAA(Indole3- Acetic Acid)
- Indole-3-acetaldehyde,
- Indole-3-pyruvic acid
- Indole-3-acetonitrile
- Indole-3-ethanol
- Phenyl acetic acid
Synthetic Auxins
- Indole 3- Butyric Acid (IBA)
- Indole 3-propionic acid
- Indole Pyruvic acid
- NAA- Napthelene Acetic acid
- 2,4,D- 2,4, Dichlorophenoxy acetic acid
Major effect of auxin? cell elongation
- Cell division and differentiation
- Prevention of lodging: Naphthyl acetamide is commonly used
Healing of injury in plants by the application of auxins is due to the secretion of traumatic acid (wound hormone)
2, 4-D : high concentration toxic to dicots (broad
leaved plants) but monocots are resistant.
Mode of action of 2,4-D as a weedicide?
Increased metabolic activity and ethylene production leading to
early senescence and disordered morphogenesis
2, 4-D +2, 4, 5-T more effective
2, 4-D +2, 4, 5-T more effective
What is ‘agent orange’?
Agent orange used by US military to defoliate forests in parts
of South Vietnam was 2,4-D +2,4,5-T
Auxin synthesis :Auxin Precursor: Amino acid Tryptophan. The essential element
required for the synthesis for tryptophan is zinc.
- 4 pathways
- IPA indole-3- pyruvic acid pathway
- TAM (tryptamine pathway)
- IAN (indole-3-acetonitrile pathway)
- IAM (indole-3-acetamide pathway)
Auxin destruction
- photo oxidation
- enzymic oxidation by IAA oxidase
- Polar transport of auxin is an active process that involves carriers
- Basipetal transport in the shoot apex (from top to base)
- Acropetal transport in the root (from base to top).
Mechanism of auxin transport: Chemiosmotic hypothesis based on two propositions
- Proton Motive Force(PMF) : a pH gradient is created along the plasma membrane that facilitate the transport of auxin.
- IAA efflux carrier: auxin transporting cells have IAA efflux carrier in their basal part. Auxin can enter cells through by diffusion or influx transporters like AUX I in the plasma membrane and moves out through efflux transporters called PIN proteins: transmembrane proteins inserted in localized portions of the PM.
What are PIN proteins? Are auxin efflux transporters.
What are Phytotropins? Are inhibitors of polar transport (auxin transport inhibitors).
Phytotropins: 3 well known examples
a) Morphactins (9-hydroxyflourine-9-carboxylic acid)
b) TIBA (2,3,5-triiodo benzoic acid)
c) NPA (Naphthylphtalamic acid)
- Mode of action: preventing auxin efflux
- Natural phytotropin : flavonoids
Auxin > increased proton pumping > H+ to acidify cell wall > cell wall loosens (expansin protein catalyze pH dependent wall extension growth > turgor pressure pushes loosened wall and growth occurs.
Proteins involved in auxin action - ABPI (Auxin binding protein I)
- Transport inhibitor response protein
Tags:
agent orange
Auxin binding
auxin efflux
Auxin Precursor
auxin transport
expansin
Natural Auxin
PCIB
Phytotropins?Anti auxins?
PIN proteins?
plant hormone
Synthetic Auxin
wound hormone