Biosynthesis of IAA

Biosynthesis of Auxins:- 

> It is biosynthesized from the amino acid tryptophan. Zinc ions are required for the synthesis of auxin. IAA or Indole acetic acid is structurally related to amino acid tryptophan.

Tryptophan dependent pathway:- Since the 1930s, when K.V. Thimann first observed the synthesis of IAA in the mold Rhizopus suinus, which had been fed the tryptophan, the conversion of tryptophan to IAA has been studied in vivo in more than 20 different plant species and in vitro with atleast 10 different cell free enzyme preparations.

> IPA pathway is found in most higher plants. 

> Species generally not having IPA pathway have TAM pathway (here, deamination and decarboxylation reactions are reversed). Tomato has both IPA and TAM pathways.

> IAN pathway is mostly present in members of the families Brassicaceae, Poaceae, and

Musaceae. Recently, nitrilase like genes are identified in Cucurbitaceae, Solanaceae, Fabaceae,

and Rosaceae.

> IAM pathway is present in pathogenic bacteria.