Plant siderophores

PLANT SIDEROPHORES

Siderophores (greek: "iron carrier") , high-affinity iron chelating compounds having low molecular weight secreted by microorganisms such as bacteria, fungi and grasses under low iron stress. They are amongst the strongest soluble fe3+ binding agents known.

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

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

IRON IS AN ESSENTIAL ELEMENT FOR BOTH PLANTS AND MICROBES

• 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

PLANT SIDEROPHORE AND ACTION • 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.

BIOSYNTHESIS OF PHYTO-SIDEROPHORESIron balance in plant is maintains through

transcriptional control of gene expressionferritin mRNA in response to iron overloadFRO2,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)

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

SIDEROPHORE AND USES 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 reducedThereby, 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)

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