action of chelating compounds in roots of plants

3. PHYTOSIDEROPHORES
• Phytosiderophores have a different structure having two α-
aminocarboxylate binding centers, together with a single α-
hydroxycarboxylate unit. this latter bidentate function
provides phytosiderophores with a high selectivity for iron

4. Although there is sufficient iron in most soils for plant
growth, plant iron deficiency is a problem in calcareous
soil, due to the low solubility of iron hydroxide.
Calcareous soil accounts for 30% of the world's farmland

5. • Numerous metabolic activities
• Electron transport system
• Formation of heme
• Act as cofactors for enzymes
• Synthesis of chlorophyll
• In the presence of oxygen, iron converts to oxyhydroxide, which is
relatively a less soluble complex

6. • 1) Under iron deficency conditions graminaceous plants (grasses, cereals and
rice) secrete phytosiderophores into the soil,
• A typical example being deoxymugineic acid.
• solubilize inorganic Fe compounds by chelation,
• 2 ) In case of Non Graminaceous plants Phytosiderophores increase their ferric
reduction capacity at the root surface,
• Under both plants transportation of Fe ion is through the Fe transporter in the
plasma membrane using a proton symport mechanism.
• The iron complex is then reduced to iron and the iron is transferred
to nicotianamine
• Nicotianamine translocate iron in phloem to all plant parts.

7. Iron balance in plant is maintains through transcriptional
control of gene expression
ferritin mRNA in response to iron overload
FRO2,IRT1, and IRT2 mRNAs respond to iron deficiencies
 Phytosiderophores are composed of a family of
mugineic acids (MAs)
Include mugineic acid (MA), 2-deoxymugineic acid
(DMA), 3-epihydroxymugineic acid (epi-HMA), and 3-
epihydroxy 2-deoxymugineic acid (epi-HDMA)

8. First step condensation of three molecules of S-adenosyl methionine
(SAM) to produce one molecule of nicotianamine (NA)
The critical enzyme in the specific pathway in grasses is the
nicotianamineaminotransferase (NAAT) that catalyzes the transfer of
an amino residue to NA
Resulting in the production of 2 -deoxymugineic acid (DMA) which is
the precursor of all other MAs
In contrast to the biosynthetic pathway of MAs, the molecular
mechanisms of MAs secretion remain unclear

9. It is well documented that heavy metals possess a negative effect
against IAA hormone( Dimkpa C, et al 2008 )
Interestingly it has observed that, in the presence of siderophores
the IAA degradation was reduced
Thereby, it enhances the ability of plant to withstand against heavy
metal stress ( Neubauer U, et al)
Siderophores promote auxin synthesis in the presence of Al3+,
Cd2+, Cu2+and Ni2+ by chelating them, and the chelation makes
the metals less able to inhibit auxins synthesis.
(Seneviratne M and Vithanage M 2015)

10. Siderophore also reduces stress to the plant by helping the ACC
deaminase in a way of interior translocation of ACC through root to
soil .
In the presence of heavy metals, it causes destruction in membrane
bound ferric reductase enzyme, and thereby declines the fe uptake in
plant. this fe deficiency exhibits as young leaf chlorosis this can be
controlled by plant trough siderophores