Agriculture Reference
In-Depth Information
phytoremediation technology for enhancing metal removal by plants (Jing
et al.
2007
). Furthermore, rhizobacteria affect the adsorption/desorption of metals
by altering their chemical properties, pH, organic matter content, redox state, etc.,
consequently affecting their solubility and mobility (Gray et al.
1998
). PGPR also
improve the efficiency of phytoremediation strategy of metal cleanup by increasing
the hyper-accumulating abilities of certain plants through their rapid growth in
metal stress (Varsha et al.
2011
).
11.5.1.4 P Solubilization
The amount of P available to plants is very less as compared to total soil P pool. One
of the important attributes of PGPR is phosphate solubilization and the group of
microorganisms capable of converting inorganic P into soluble forms is known as
P-solubilizing microorganisms (Khan et al.
2007
). Along with P assimilation, these
microorganisms release a fair amount of soluble P into soil which can be used as P
source by the plants. The most efficient PS bacterial strains are
Pseudomonas
(Das
et al.
2003
) and
Rhizobium
(Sridevi and Mallaiah
2009
), whereas
Penicillium
(Chai
et al.
2011
) and
Aspergillus
(Singh and Reddy
2011
) are the most powerful fungal
PS strains (Khan et al.
2010
; Brahmaprakash and Sahu
2012
).
11.5.1.5
Improves Plant Defense Mechanisms Under Stressed
Environment
Modulating Enzyme: 1-Aminocyclopropane-1-Carboxylate Deaminase
Under normal condition, plant maintains its homeostasis by producing a hormone
“ethylene” which plays important role in various developmental processes.
Under stress conditions, the amount of ethylene produced by plant increases
due to which it is also known as “stress ethylene.” At higher concentrations, it
decreases root and shoot growth and also induces defense responses of plant to
mitigate adverse effects. Plant growth-promoting rhizobacteria produce an enzyme
1-aminocyclopropane-1-carboxylate (ACC) deaminase, which degrades ACC, the
precursor for ethylene, into ammonia and
-ketobutyrate. Bacteria utilize ammonia
as N source thereby restricting the ethylene accumulation consequently rescuing the
plant growth from the stress (Khan et al.
2009
). Also, PGPR synthesize growth
hormone IAA from tryptophan produced in plant root exudates which in turn
enhances both plant growth and activates enzyme ACC synthase involved in
ACC production. ACC so produced is then exuded from the plant roots and
acted upon by the bacteria (Selvakumar et al.
2012
).
α
