Iron oxidation on the surface of adventitious roots and its relation to aerenchyma formation in rice genotypes

Abstract

Establishment of the water layer in an irrigated rice crop leads to consumption of free oxygen in the soil which enters in a chemical reduction process mediated by anaerobic microorganisms, changing the crop environment. To maintain optimal growth in an environment without O2, rice plants develop pore spaces (aerenchyma) that allow O2 transport from air to the roots. Carrying capacity is determined by the rice genome and it may vary among cultivars. Plants that have higher capacity for formation of aerenchyma should theoretically carry more O2 to the roots. However, part of the O2 that reaches the roots is lost due to permeability of the roots and the O2 gradient created between the soil and roots. The O2 that is lost to the outside medium can react with chemically reduced elements present in the soil; one of them is iron, which reacts with oxygen and forms an iron plaque on the outer root surface. Therefore, evaluation of the iron plaque and of the formation of pore spaces on the root can serve as a parameter to differentiate rice cultivars in regard to the volume of O2 transported via aerenchyma. An experiment was thus carried out in a greenhouse with the aim of comparing aerenchyma and iron plaque formation in 13 rice cultivars grown in flooded soils to their formation under growing conditions similar to a normal field, without free oxygen. The results indicated significant differences in the volume of pore spaces in the roots among cultivars and along the root segment in each cultivar, indicating that under flooded conditions the genetic potential of the plant is crucial in induction of cell death and formation of aerenchyma in response to lack of O2. In addition, the amount of Fe accumulated on the root surface was different among genotypes and along the roots. Thus, we concluded that the rice genotypes exhibit different responses for aerenchyma formation, oxygen release by the roots and iron plaque formation, and that there is a direct relationship between porosity and the amount of iron oxidized on the root surface.

Iron Plaque: A Shield against Soil Contamination and Key to Sustainable Agriculture

“…A wide variety of plants were proven to form IP, comprising underwater plants, emergent plants, terrestrial plants in aquatic environments, and so on. Representatives of Previous studies have shown that IP is more likely to occur in acidic pH environments [61,62]. After a series of redox reactions, it ultimately precipitates on the root surface in the form of Fe 2 O 3 or Fe(OH) 3 [20].…”

“…In the middle and late stages, through the equation of 4Fe(II) + 10H2O + O2 → 4Fe(OH)3 + 8H + [58][59][60], Fe(II) is transformed into iron oxide, which precipitates on the surface of the roots, thus forming IP and protecting plant roots from HMs via adsorption. Previous studies have shown that IP is more likely to occur in acidic pH environments [61,62]. After a series of redox reactions, it ultimately precipitates on the root surface in the form of Fe2O3 or Fe(OH)3 [20].…”

“…Previous studies have shown that IP is more likely to occur in acidic pH environments [ 61 , 62 ]. After a series of redox reactions, it ultimately precipitates on the root surface in the form of Fe 2 O 3 or Fe(OH) 3 [ 20 ].…”

West Sumatera Brown Rice Resistance to Fe

“…Aerenchyma was formed up to 20-50% of the total volume of rice root in a flooded condition. The aerenchyma formation was started from 2-4 weeks after planting, and the highest oxidation ability occurred in the maximum tiller formation stage [39]. The Fe concentration did not affect the total of the tiller ( Table 3).…”