H₂O₂ mediates nitrate‐induced iron chlorosis by regulating iron homeostasis in rice

Abstract

The uptake of nitrate by plant roots causes a pH increment in rhizosphere and leads to iron (Fe) deficiency in rice. However, little is known about the mechanism how the nitrate uptake-induced high rhizosphere pH causes Fe deficiency. Here, we found that rice showed severe leaf chlorosis and large amounts of Fe plaque were aggregated on the root surface and intercellular space outside the exodermis in a form of ferrihydrite under alkaline conditions. In this case, there was significantly decreased Fe concentration in shoots, and the Fe deficiency responsive genes were strongly induced in the roots. The high rhizosphere pH induced excess hydrogen peroxide (H O ) production in the epidermis due to the increasing expression of NADPH-oxidase respiratory burst oxidase homolog 1, which enhanced root oxidation ability and improved the Fe plaque formation in rhizosphere. Further, the concentrated H O regulated the phenylpropanoid metabolism with increased lignin biosynthesis and decreased phenolics secretion, which blocked apoplast Fe mobilization efficiency. These factors coordinately repressed the Fe utilization in rhizosphere and led to Fe deficiency in rice under high pH. In conclusion, our results demonstrate that nitrate uptake-induced rhizosphere alkalization led to Fe deficiency in rice, through H O -dependent manners of root oxidation ability and phenylpropanoid metabolism.

Overexpression of a High-Affinity Nitrate Transporter OsNRT2.1 Increases Yield and Manganese Accumulation in Rice Under Alternating Wet and Dry Condition

“…However, Mn uptake drastically increased in the transgenic lines in 0.5 mM NO 3 - ( Supplementary Figure S5 and Figure 4D ). It was recently shown that NO 3 - uptake induces external alkalization, reducing Fe/Mn concentrations by enhancing the levels of H 2 O 2 in rice ( Chen et al, 2018 ). In this study, we performed hydroponic experiments in MES buffered nutrient medium (to control pH) and nutrient treatments were replaced every 2 days.…”

Assessment of Subcellular ROS and NO Metabolism in Higher Plants: Multifunctional Signaling Molecules

“…Nitrate root uptake increases pH in the rice rhizosphere, which triggers Fe deficiency. This is due to an increase in H 2 O 2 induced by RBOH1, with a concomitant boost in lignin biosynthesis and low phenolic secretion, which blocks apoplastic Fe mobilization efficiency [161].…”

A Comparative Assessment of Measures of Leaf Nitrogen in Rice Using Two Leaf-Clip Meters

“…For example, SPAD value decreased or increased after a change in petiole nitrate concentration. Chen et al [17] found that when nitrate-N was the only N source, the increase of rhizosphere pH led to the slow growth and yellowing of new leaves, which was mainly attributed to an increase of phenolic compounds in the phenylpropane metabolism pathway in roots under high pH conditions. Meanwhile, Schijlen et al [18] also found that more rutin and other flavonoid polyphenols appeared when Arabidopsis thaliana seedlings grew for two days under N deficiency conditions.…”