Agriculture Reference
In-Depth Information
Fig. 2.3
Indoleacetic acid affecting various stages of plant development
Physiological Functions of IAA
The production of phytohormones such as auxins by microbial communities has
been reported by various workers over the last 20 years (Giordano et al.
1999a
,
b
;
Rajkumar and Freitas
2008
; Singh
2008
; Ahemad and Khan
2012
). Among plant
hormones, auxins are the major plant growth regulators produced by PSM (Oves
et al.
2013
) and exhibit many physiological functions as shown in Fig.
2.3
. Apart
from varying physiological functions of IAA, the role of IAA in legume-
Rhizobium
symbiosis is briefly discussed in the following section.
Role of Indoleacetic Acid in Legume-
Rhizobium
Symbiosis
Among nodule bacteria, rhizobial strains have been reported to produce auxins in
variable amounts. For example, Vargas et al. (
2009
) in a study reported consider-
ably lower frequency of auxin producers (23 %) among populations of clover
nodulating
R. leguminosarum
bv.
trifolii
. The auxins so released by nodule bacteria
are reported to affect nodulation, and accordingly, IAA synthesizing rhizobia have
been found to produce more nodules than IAA-negative mutants (Boiero
et al.
2007
). The IAA produced by rhizobia may also induce root morphogenesis
and consequently enhance its (1) size and weight, (2) branch numbers and patterns
and (3) the surface area of roots as reported in non-legumes (Dazzo and Yanni
