Iron plaque formation, characteristics, and its role as a barrier and/or facilitator to heavy metal uptake in hydrophyte rice (Oryza sativa L.)

Speciation and distribution of chromium (III) in rice root tip and mature zone: The significant impact of root exudation and iron plaque on chromium bioavailability

“…Among them, primary roots are classified into root tips and mature root regions according to the level of development (Seyferth et al, 2010;Zandi et al, 2022). Root tips have underdeveloped vascular systems, lacking the complete formation of the aerenchyma and Casparian bands (CBs).…”

“…Similarly to many aquatic or semi-aquatic plants, rice is a hydrophyte species grown in flooded paddy fields. Rice has to cope with anaerobic conditions by radial oxygen diffusion from the root aerenchyma towards the root surface and adjacent rhizosphere , where it mediates iron oxidation [Fe (II) to Fe (III)] and development of an amorphous coating of iron (hydr)oxides (known as iron plaque, IP) on the root surface Tripathi et al, 2014;Zandi et al, 2022). Moreover, continuous flooding was indicated to create a favourable rhizosphere environment for IP formation (Xiao et al, 2021).…”

“…There is consensus that root capacity for aerobic respiration is the main factor in the oxidising power of the rhizoplane zone (Wu et al, 2012;, and consequently the degree of IP formation (Zandi et al, 2022). Rice root tips with no discernible aerenchyma structures were found to have a higher oxygen discharge in comparison to the basal part of the root .…”

“…Many studies concerning the whole root system have shown that iron (hydr)oxides have a strong binding affinity for metal(loid) ions on the root surface and reduce their mobility and bioavailability, thereby inhibiting the uptake and transport of toxic metals, including Cr Zandi et al, 2022). Previous studies have shown that in the absence or weak presence of IP, higher concentrations of Cr were accumulated in root cells rather than in shoots of rice Zandi et al, , 2021, suggesting that Cr mainly deposited in root cell walls hindered its transport to the aerial organs .…”

Zinc Fertilizers Modified the Formation and Properties of Iron Plaque and Arsenic Accumulation in Rice (Oryza sativa L.) in a Life Cycle Study

“…Iron plaques, containing both amorphous and crystalline iron (oxyhydr)­oxides, are formed on the root surface when Fe 2+ in soil pore water is oxidized by molecular oxygen released from rice aerenchyma. − Iron plaques play an important role in plant As uptake because they can act as a protective barrier against As accumulation in rice roots as a result of their high adsorption capacity. ,− In addition to their formation, the composition of iron plaques is also critical. For example, amorphous iron (oxyhydr)­oxides and weak crystalline ferrihydrite generally display higher adsorption capacity for As than fine-ordered crystalline structures. , Thus, the amount of iron plaque formation and their composition structure can markedly affect As accumulation in rice grains.…”