The relationship between activation energy and the rate constant of the reaction, k, is given by the Arrhenius equation

Arrhenius equation

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

TLS Online TPP Program

#Id: 10120

#Unit 6. System Physiology – Plant

In maize kernels, IAA also appears to be synthesized by a tryptophan independent pathway via indole-3- glycerol phosphate

TLS Online TPP Program

#Id: 10121

#Unit 6. System Physiology – Plant

Covalent conjugation of amino acids to IAA can also result in permanent inactivation.

TLS Online TPP Program

#Id: 10122

#Unit 6. System Physiology – Plant

The IAA conjugate to Asp or Glu causes irreversibly degraded to the oxIAA conjugate. IAMT1, indole-3-acetate O-methyltransferase1.