title: Plants fabricate Fe-nanocomplexes at root surface to counter and phytostabilize excess ionic Fe.
abstract: While evaluating the impact of iron nanoparticles (NPs) on terrestrial plants we realized potential of root system of intact plants to form orange-brown complexes constituted of NPs around their roots and at bottom/side of tubes when exposed to FeCl3. These orange-brown complexes/plaques seen around roots were similar to that reported in wetland plants under iron toxicity. Transmission electron microscopy coupled with energy dispersive X-ray analysis revealed that orange-brown complexes/plaques, formed by root system of all 16 plant species from 11 distinct families tested, were constituted of NPs containing Fe. Selected area electron diffraction and powder X-ray diffraction spectra showed their amorphous nature. Thermogravimetric and fourier transform infra-red analysis showed that these Fe-NPs/nanocomplexes were composed of iron-oxyhydroxide. These plant species generated orange-brown Fe-NPs/nanocomplexes even under strict sterile conditions establishing inbuilt and independent potential of their root system to generate Fe-NPs. Root system of intact plants showed ferric chelate reductase activity responsible for reduction of Fe(3+) to Fe(2+). Reduction of potassium ferricyanide by root system of intact plants confirmed that root surface possess strong reducing strength, which could have played critical role in reduction of Fe(3+) and formation of Fe-NPs/nanocomplexes. Atomic absorption spectrophotometric analysis revealed that majority of iron was retained in Fe-nanocomplexes/plaques, while only 2-3 % was transferred to shoots, indicating formation of nanocomplexes is a phytostabilization mechanism evolved by plants to restrict uptake of iron above threshold levels. We believe that formation of Fe-NPs/nanocomplexes is an ideal homeostasis mechanism evolved by plants to modulate uptake of desired levels of ionic Fe.
authors.affiliation: Department of Environmental Studies, University of Delhi, Delhi, 110007, India, ppsaradhi@gmail.com.
authors.forename: P
authors.initials: P
authors.lastname: Pardha-Saradhi
authors.forename: G
authors.initials: G
authors.lastname: Yamal
authors.forename: Tanuj
authors.initials: T
authors.lastname: Peddisetty
authors.forename: P
authors.initials: P
authors.lastname: Sharmila
authors.forename: Jyoti
authors.initials: J
authors.lastname: Singh
authors.forename: Rajamani
authors.initials: R
authors.lastname: Nagarajan
authors.forename: K S
authors.initials: KS
authors.lastname: Rao
mesh_terms: D007477:Ions / Q000737:chemistry / Q000378:metabolism; D007501:Iron / Q000737:chemistry* / Q000378:metabolism*; D019684:Magnoliopsida / Q000737:chemistry / Q000378:metabolism*; D053768:Metal Nanoparticles / Q000737:chemistry; D010316:Particle Size; D018517:Plant Roots / Q000737:chemistry / Q000378:metabolism*; D013499:Surface Properties
chemical_list: D007477:Ions; D007501:Iron