14 Siderophore in Plant Nutritional Management …
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14.3 Shuttling Mechanism Through Siderophore Mediated
Iron Transporter System
Fe is considered as the key regulatory element of cellular metabolic pathway. It
regulates the activity of many antioxidative enzymes like catalase, peroxidase (POD),
ascorbate, and superoxide dismutase. Deficiency of Fe in plant system may affect
oxidative defensive system and cause oxidative injury. Therefore, all the living beings
are required a well-organized and controlled system of Fe absorption and utilization.
Siderophore by forming a multi-complex system with the nutrient molecules play
an important role in the transportation of ferric ions into the plant cell. Specific
siderophore receptors are present on the cell membrane which helps in transporting
the siderophore–iron complex to the cell interior.
14.4 Cell Membrane Siderophore Receptors
There are different types of siderophore specific receptors present in different types of
gram-positive and gram-negative bacteria. Gram-negative bacteria (e.g., Escherichia
sp.) possess receptor specifically on the outer membrane that recognize the Fe (III)–
siderophore complexes at the cell surface (Krewulak and Vogel 2008) whereas grampositive bacteria (e.g., Bacillus sp.), lacks the outer membrane and their receptor
molecules. Therefore, periplasmic siderophore receptor helps in binding Fe (III)–
siderophore complexes (Fukushima et al. 2013). Fec A and Fep A protein receptors
are present on the outer membrane, whereas Ton B-Exb B complex siderophore
receptor is present on the inner membrane. Fec CDE- Fep CDE- ATP dependent
carrier molecules are present as an inner membrane and periplasmic transporting
proteins.
14.5 Channel of Fe Transportation in Microbes and Plants
When the siderophore is released from the cell, the membrane receptors protein binds
with iron and forms iron–siderophore complex and transported into the cell via Fec
A and Fep A (an outer membrane receptor), then it is transported to Fec CDE- Fep
CDE an ATP-dependent transporter systems (or ABC-Transporter systems). Finally,
siderophore–iron complex is released into the cytosol with the help of membrane
receptor protein Ton B. In the cytoplasm, iron is released from the complex via
hydrolytic breakdown in the presence of NADPH linked siderophore reductase and
Ent ABCD protein. Such produced Fe
++ does not have a high affinity with siderophore
and it separates from the siderophore–iron complex. The released siderophores either
get degraded or recycled by excretion through efflux pumping system (Table 14.2).
321
14.3 Shuttling Mechanism Through Siderophore Mediated
Iron Transporter System
Fe is considered as the key regulatory element of cellular metabolic pathway. It
regulates the activity of many antioxidative enzymes like catalase, peroxidase (POD),
ascorbate, and superoxide dismutase. Deficiency of Fe in plant system may affect
oxidative defensive system and cause oxidative injury. Therefore, all the living beings
are required a well-organized and controlled system of Fe absorption and utilization.
Siderophore by forming a multi-complex system with the nutrient molecules play
an important role in the transportation of ferric ions into the plant cell. Specific
siderophore receptors are present on the cell membrane which helps in transporting
the siderophore–iron complex to the cell interior.
14.4 Cell Membrane Siderophore Receptors
There are different types of siderophore specific receptors present in different types of
gram-positive and gram-negative bacteria. Gram-negative bacteria (e.g., Escherichia
sp.) possess receptor specifically on the outer membrane that recognize the Fe (III)–
siderophore complexes at the cell surface (Krewulak and Vogel 2008) whereas grampositive bacteria (e.g., Bacillus sp.), lacks the outer membrane and their receptor
molecules. Therefore, periplasmic siderophore receptor helps in binding Fe (III)–
siderophore complexes (Fukushima et al. 2013). Fec A and Fep A protein receptors
are present on the outer membrane, whereas Ton B-Exb B complex siderophore
receptor is present on the inner membrane. Fec CDE- Fep CDE- ATP dependent
carrier molecules are present as an inner membrane and periplasmic transporting
proteins.
14.5 Channel of Fe Transportation in Microbes and Plants
When the siderophore is released from the cell, the membrane receptors protein binds
with iron and forms iron–siderophore complex and transported into the cell via Fec
A and Fep A (an outer membrane receptor), then it is transported to Fec CDE- Fep
CDE an ATP-dependent transporter systems (or ABC-Transporter systems). Finally,
siderophore–iron complex is released into the cytosol with the help of membrane
receptor protein Ton B. In the cytoplasm, iron is released from the complex via
hydrolytic breakdown in the presence of NADPH linked siderophore reductase and
Ent ABCD protein. Such produced Fe
++ does not have a high affinity with siderophore
and it separates from the siderophore–iron complex. The released siderophores either
get degraded or recycled by excretion through efflux pumping system (Table 14.2).