72
complexing with them (Renshaw et al. 2002; Duckworth et al. 2009; Harrington
et al. 2015).
Considering the adverse effects of agrochemicals on soil health, the environment, and the biotic community, including humans, the siderophore can ideally be
used in the agriculture system as they not only enhance mineral availability but also
biologically control the pests and pathogens of crop plant. Several workers have
reported the role of siderophore as a biocontrol agent to suppress phytopathogens
(Tariq et al. 2010; Sasirekha and Srividya 2016). Pandey et al. (2005) demonstrated
siderophore-mediated growth enhancement in Indian mustard. There are reports on
siderophore-mediated phytoextraction and bioremediation of metal-contaminated
environment (Hernlem et al. 1999; Rajkumar et al. 2010; Gaonkar and Bhosle
2013). Siderophore also helps in soil mineral weathering (Ahmed and
Holmstrom 2014).
5.6 Mechanism of Action
Plant cell decreases hydrophobicity under low-available iron environment generating iron deficiency signals. Siderophores are low-molecular-weight proteins that
chelate the iron more efficiently and make them available to the plants or microbes.
In the cellular environment, the ferric iron is converted into ferrous iron, which
remains available for utilization by microbes and plants. Many of the siderophoreproducing bacteria may stimulate plant growth by ensuring iron availability to
plants and by producing phytohormones and organic acids that solubilize phosphate
and other lithospheric nutrients present in soil in complex state. Siderophores can
play a role in the prevention of pathogenic microbes from plants by depriving iron
and elicit induced resistance. Liu et al. (2007) have shown that pathogen attack
depletes the intracellular iron leading to transcription of pathogenesis-related genes
for oxidative burst regulating the plant defense. Saxena (2003) reported transcript
accumulation for peroxidase and phenylalanine lyase during induction of systemic
resistance in pear millet against downy mildew disease as expressed by inoculation
with plant growth-promoting rhizobacteria (PGPR) (Figs. 5.1 and 5.2).
Many siderophore-producing bacterial and fungal strains promote plant growth
by enhancing iron solubility. Thus, siderophore chelates the iron and makes it available to the plants. Han et al. (2018) identified the role of sip gene in iron absorption
in Vibrio anguillarum 775. Siderophore-interacting proteins (SIPs) by utilizing ferric siderophore complex make the ferrous iron available to microbial system.
Defense response genes are induced in both incompatible and compatible plant–
pathogen interaction. However, mRNA accumulation for many plant defense genes
is more rapid during interaction involving plant expressing resistance (R) gene corresponding to virulence gene of the pathogen (Christensen et al. 2002; Davis et al.
2002). There are studies related with differential transcript accumulation in multicell hypersensitive response interaction (Burrow et al. 2000; Fossdal et al. 2001;
Christensen et al. 2002).
A. Saxena
complexing with them (Renshaw et al. 2002; Duckworth et al. 2009; Harrington
et al. 2015).
Considering the adverse effects of agrochemicals on soil health, the environment, and the biotic community, including humans, the siderophore can ideally be
used in the agriculture system as they not only enhance mineral availability but also
biologically control the pests and pathogens of crop plant. Several workers have
reported the role of siderophore as a biocontrol agent to suppress phytopathogens
(Tariq et al. 2010; Sasirekha and Srividya 2016). Pandey et al. (2005) demonstrated
siderophore-mediated growth enhancement in Indian mustard. There are reports on
siderophore-mediated phytoextraction and bioremediation of metal-contaminated
environment (Hernlem et al. 1999; Rajkumar et al. 2010; Gaonkar and Bhosle
2013). Siderophore also helps in soil mineral weathering (Ahmed and
Holmstrom 2014).
5.6 Mechanism of Action
Plant cell decreases hydrophobicity under low-available iron environment generating iron deficiency signals. Siderophores are low-molecular-weight proteins that
chelate the iron more efficiently and make them available to the plants or microbes.
In the cellular environment, the ferric iron is converted into ferrous iron, which
remains available for utilization by microbes and plants. Many of the siderophoreproducing bacteria may stimulate plant growth by ensuring iron availability to
plants and by producing phytohormones and organic acids that solubilize phosphate
and other lithospheric nutrients present in soil in complex state. Siderophores can
play a role in the prevention of pathogenic microbes from plants by depriving iron
and elicit induced resistance. Liu et al. (2007) have shown that pathogen attack
depletes the intracellular iron leading to transcription of pathogenesis-related genes
for oxidative burst regulating the plant defense. Saxena (2003) reported transcript
accumulation for peroxidase and phenylalanine lyase during induction of systemic
resistance in pear millet against downy mildew disease as expressed by inoculation
with plant growth-promoting rhizobacteria (PGPR) (Figs. 5.1 and 5.2).
Many siderophore-producing bacterial and fungal strains promote plant growth
by enhancing iron solubility. Thus, siderophore chelates the iron and makes it available to the plants. Han et al. (2018) identified the role of sip gene in iron absorption
in Vibrio anguillarum 775. Siderophore-interacting proteins (SIPs) by utilizing ferric siderophore complex make the ferrous iron available to microbial system.
Defense response genes are induced in both incompatible and compatible plant–
pathogen interaction. However, mRNA accumulation for many plant defense genes
is more rapid during interaction involving plant expressing resistance (R) gene corresponding to virulence gene of the pathogen (Christensen et al. 2002; Davis et al.
2002). There are studies related with differential transcript accumulation in multicell hypersensitive response interaction (Burrow et al. 2000; Fossdal et al. 2001;
Christensen et al. 2002).
A. Saxena