14 Siderophore in Plant Nutritional Management …
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sustainable soil fertility as well as plant growth (Tilak et al. 2005). PGPB supports
the growth of plants through phosphorus solubilization, nitrogen fixation, absorption and assimilation of minerals/nutrients. These Endophytic bacteria also produce
siderophore and many phytohormones which support the plant life in adverse stressful
condition (Glick 1995; Bhardwaj et al. 2014; Pahari et al. 2016) (Table 14.1).
Siderophores have potential roles and applications in various areas of environmental research due to their affinity in metal binding especially with iron. Chemically siderophores are the iron-containing low molecular weight chelating agents,
showing specific affinity with ferric ions, therefore, siderophores can be termed as
“Fe-biosensors.” They facilitate bioremediation, weathering of soil-mineral particles, and enhanced plant growth. Most of the aerobic and facultative anaerobic
microorganisms like Pseudomonas, Azotobacter, Bacillus, Enterobacter, Serratia,
Azospirillum, and Rhizobium (Glick et al. 1999; Loper and Henkels 1999; Pahari and
Mishra 2017) synthesize siderophore under iron-limited conditions (Neilands 1981).
As per research report, all microbes do not require iron and siderophores. There are
some lactic acid-producing bacteria which showed poor growth in iron-containing
medium because they don’t have iron regulating ribotide reductase enzyme. Iron is
the fourth most abundant element on the earth, an essential micronutrient for plant
growth, though deemed as most lacking micronutrients due to its insoluble nature
of Fe
+3 . The preliminary role of siderophores is scavenging of Fe. They also form
complex molecules with other essential micro-elements like Mo, Mn, Co, and Ni
in the environment and make them available for microbial cells (Bellenger et al.
2008; Braud et al. 2009a, b). There are no specific and defined procedures for the
isolation of siderophores, as they differ substantially in their structures. Detection
of siderophores can be finished by paper electrophoresis method whereas; structural
characterization is best carried out by NMR and mass spectroscopy. In this chapter we
will focus on the structure, functions, and applications of siderophores specifically
in nutrient absorption by crop plants in the agriculture field.
14.2 Types of Siderophore
At present nearly 500 siderophores are reported from selected microorganisms.
A great variation is seen in siderophore structure from one species to another.
Broadly such siderophore is classified into two (a) Microbial siderophore, and (b)
Phytosiderophore.
(a) Microbial siderophores: According to the oxygen ligands for Fe
3+ organization bacterial siderophores can be differentiated into three main categories, namely,
catecholate (i.e., enterobactin), carboxylates (i.e., rhizobactin), and hydroxamates
(i.e., ferrioxamine B) (Matzanke1991). However, there is also a certain type of
microbial siderophores that contain a mix of the main functional groups (i.e., pyoverdine) (Cornelis 2010). One such most common fungal siderophores is hydroxamates
belonging to the ferrichrome family (i.e., ferrichrome), which is further divided into
317
sustainable soil fertility as well as plant growth (Tilak et al. 2005). PGPB supports
the growth of plants through phosphorus solubilization, nitrogen fixation, absorption and assimilation of minerals/nutrients. These Endophytic bacteria also produce
siderophore and many phytohormones which support the plant life in adverse stressful
condition (Glick 1995; Bhardwaj et al. 2014; Pahari et al. 2016) (Table 14.1).
Siderophores have potential roles and applications in various areas of environmental research due to their affinity in metal binding especially with iron. Chemically siderophores are the iron-containing low molecular weight chelating agents,
showing specific affinity with ferric ions, therefore, siderophores can be termed as
“Fe-biosensors.” They facilitate bioremediation, weathering of soil-mineral particles, and enhanced plant growth. Most of the aerobic and facultative anaerobic
microorganisms like Pseudomonas, Azotobacter, Bacillus, Enterobacter, Serratia,
Azospirillum, and Rhizobium (Glick et al. 1999; Loper and Henkels 1999; Pahari and
Mishra 2017) synthesize siderophore under iron-limited conditions (Neilands 1981).
As per research report, all microbes do not require iron and siderophores. There are
some lactic acid-producing bacteria which showed poor growth in iron-containing
medium because they don’t have iron regulating ribotide reductase enzyme. Iron is
the fourth most abundant element on the earth, an essential micronutrient for plant
growth, though deemed as most lacking micronutrients due to its insoluble nature
of Fe
+3 . The preliminary role of siderophores is scavenging of Fe. They also form
complex molecules with other essential micro-elements like Mo, Mn, Co, and Ni
in the environment and make them available for microbial cells (Bellenger et al.
2008; Braud et al. 2009a, b). There are no specific and defined procedures for the
isolation of siderophores, as they differ substantially in their structures. Detection
of siderophores can be finished by paper electrophoresis method whereas; structural
characterization is best carried out by NMR and mass spectroscopy. In this chapter we
will focus on the structure, functions, and applications of siderophores specifically
in nutrient absorption by crop plants in the agriculture field.
14.2 Types of Siderophore
At present nearly 500 siderophores are reported from selected microorganisms.
A great variation is seen in siderophore structure from one species to another.
Broadly such siderophore is classified into two (a) Microbial siderophore, and (b)
Phytosiderophore.
(a) Microbial siderophores: According to the oxygen ligands for Fe
3+ organization bacterial siderophores can be differentiated into three main categories, namely,
catecholate (i.e., enterobactin), carboxylates (i.e., rhizobactin), and hydroxamates
(i.e., ferrioxamine B) (Matzanke1991). However, there is also a certain type of
microbial siderophores that contain a mix of the main functional groups (i.e., pyoverdine) (Cornelis 2010). One such most common fungal siderophores is hydroxamates
belonging to the ferrichrome family (i.e., ferrichrome), which is further divided into