phyA is rapidly degraded following its activation by light. Thus, protein degradation, in addition to phosphorylation, is emerging as a ubiquitous mechanism regulating many cellular processes, including light and hormone signaling, circadian rhythms, and flowering time.

TLS Online TPP Program

#Id: 10114

#Unit 6. System Physiology – Plant

Indole-3-acetic acid (IAA) occurs in all plants, 

Peas contain 4-chloroindole-3-acetic acid. 

Mustards and corn contain indole-3- butyric acid (IBA).

TLS Online TPP Program

#Id: 10115

#Unit 6. System Physiology – Plant

Rapidly dividing tissues, shoot apical meristems, young leaves, and developing fruits and seeds are the primary sites of IAA synthesis.

TLS Online TPP Program

#Id: 10116

#Unit 6. System Physiology – Plant

IAA is synthesises by tryptophan and is primarily synthesized in a two-step process 

Indole-3-pyruvate (IPyA) as the intermediate. 

The second step in the pathway is carried out by the YUCCA gene product, a tryptophan aminotransferase.

TLS Online TPP Program

#Id: 10117

#Unit 6. System Physiology – Plant

Auxins in biological samples can be determined by bioassay, mass spectrometry, or enzyme-linked immunosorbent assay (ELISA).

The Avena coleoptile curvature assay is a sensitive measure of auxin activity (it is effective for IAA concentrations of about 0.02 to 0.2 mg L–1).

TLS Online TPP Program

#Id: 10118

#Unit 6. System Physiology – Plant

Trp transaminase

Tryptophan (Trp)-----------------------→ Indole-3-pyruvic acid

IPA decarboxylase

(IPA) -----------------------→ Indole-3-acetaldehyde (IAld)

---------------------------------------→ Indole-3-acetic acid (IAA)

TLS Online TPP Program

#Id: 10119

#Unit 6. System Physiology – Plant

In plants that produce indole glucosinolate defense compounds, IAA can also be synthesized from tryptophan via a pathway with indole acetonitrile as an intermediate