Mechanism of Phosphate Solubilization and Physiological Functions of Phosphate-Solubilizing Microorganisms - Phosphate Solubilizing Microorganisms - page 40

Table 2.5 Examples of plant growth-promoting substances synthesized by symbiotic nitrogen
fixers
Symbiotic N 2 fixer Crop enhancer References

Rhizobium leguminosarum
RP2

ACC deaminase, IAA, HCN, siderophore,
ammonia, EPS

Bradyrhizobium MRM6 IAA, HCN, siderophore, ammonia, EPS

Rhizobium MRL3 IAA, HCN, siderophore, ammonia

Sinorhizobium strain Chitinase Qing-xia

et al. ( 2011 )

Rhizobium leguminosarum
var. Phaseoli

IAA Stajkovi´

et al. ( 2011 )

Rhizobium spp. IAA, siderophore Mehboob

et al. ( 2010 )

Sinorhizobium meliloti IAA, P-solubilization Bianco and Defez

( 2010 )

Bradyrhizobium IAA, gibberellic acid Afzal et al. ( 2010 )

Mesorhizobium

IAA

Rhizobium spp.

IAA Chakraborty

et al. ( 2009 )

Rhizobium leguminosarum IAA, siderophore

Mesorhizobium IAA, HCN, siderophore, ammonia,

P-solubilization

Rhizobium strain TAL 1145 ACC deaminase Tittabutr

et al. ( 2008 )

Rhizobium spp. IAA, gibberellic acid, zeatin Boiero et al. ( 2007 )

Mesorhizobium loti MP6 IAA, HCN, siderophore, P-solubilization Chandra

et al. ( 2007 )

Rhizobium etli USDA9032 Phenazine, antibiotic Krishnan

et al. ( 2007 )

2.3.1.1 Synthesis and Physiological Functions of Phytohormones

Synthesis of IAA

The synthesis of IAA by microbes (Fig. 2.2 ) involves one of the three pathways:
(1) Indoleacetic acid formation via indole-3-pyruvic acid and indole-3-acetic alde-
hyde is found in the majority of bacteria like Erwinia herbicola ; saprophytic species
of the genera Agrobacterium and Pseudomonas ; and certain representatives of
Bradyrhizobium , Rhizobium , Azospirillum , Klebsiella and Enterobacter. (2) The
conversion of tryptophan into indole-3-acetic aldehyde may involve an alternative
pathway in which tryptamine is formed. This pathway is believed to operate in
pseudomonads and azospirilla. (3) IAA biosynthesis via indole-3-acetamide for-
mation is reported for phytopathogenic bacteria Agrobacterium tumefaciens ,
Pseudomonas syringae and E. herbicola and saprophytic pseudomonads like
Pseudomonas putida and P. fluorescens . The genes controlling IAA synthesis via
this pathway are also reported in symbiotic bacteria like Rhizobium spp.,