The effects of different iron and phosphorus treatments on the formation and morphology of iron plaque in rice roots (Oryza sativa L)

Introduction Rice (Oryza sativa L.) is a pivotal cereal crop worldwide. It relies heavily on the presence of iron plaque on its root surfaces for optimal growth and enhanced stress resistance across diverse environmental conditions. Method To study the crystallographic aspects of iron plaque formation on rice roots, the concentrations of Fe2+ and PO43- were controlled in this study. The effects of these treatments were assessed through comprehensive analyzes encompassing root growth status, root surface iron concentration, root vitality, enzyme activities, and microstructural characteristics using advanced techniques such as root analysis, scanning electron microscopy (SEM), and ultrathin section transmission electron microscopy (TEM). Results The results demonstrated that an increase in the Fe2+ concentration or a decrease in the PO43- concentration in the nutrient solution led to improvements in various root growth indicators. There was an elevation in the DCB (dithionite-citrate-bicarbonate) iron content within the roots, enhanced root vitality, and a significant increase in the activities of the superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) enzymes. Moreover, as the Fe2+ concentration increased, amorphous iron oxide minerals on the root surface were gradually transformed into ferrihydrite particles with sizes of approximately 200 nm and goethite particles with sizes of approximately 5 mu m. This study showed that an increase in the Fe2+ concentration and a decrease in the PO43- concentration led to the formation of substantial iron plaque on the root surfaces. It is noteworthy that there was a distinct gap ranging from 0.5 to 3 mu m between the iron plaque formed through PO43- treatment and the cellular layer of the root surface. Discussion This study elucidated the impacts of Fe2+ and PO43- treatments on the formation, structure, and morphology of the iron plaque while discerning variations in the spatial proximity between the iron plaque and root surface under different treatment conditions.