National Key Laboratory of Crop Genetic Improvement, Huazhong Agricultural University, Wuhan, 430070, China.
Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtze River), Ministry of Agriculture, Wuhan, 430070, China.
Plant Cell Environ. 2018 Apr;41(4):767-781. doi: 10.1111/pce.13145. Epub 2018 Feb 9.
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.
植物根系吸收硝酸盐会导致根际 pH 值升高，从而导致水稻缺铁。然而，人们对硝酸盐吸收诱导的高根际 pH 值如何导致缺铁的机制知之甚少。在这里，我们发现，在碱性条件下，水稻表现出严重的叶片黄化，大量的铁斑聚集在根表面和表皮外细胞间隙中，以水铁矿的形式存在。在这种情况下，地上部分的铁浓度显著降低，根中缺铁应答基因强烈诱导。由于 NADPH 氧化酶呼吸爆发氧化酶同源物 1 的表达增加，高根际 pH 值导致表皮中过量的过氧化氢（H O ）产生，从而增强了根的氧化能力，改善了根际中铁斑的形成。此外，过氧化氢集中调控苯丙烷代谢，增加木质素生物合成，减少酚类分泌，从而阻止质外体铁的动员效率。这些因素协同抑制了根际中的铁利用，导致水稻在高 pH 值下缺铁。总之，我们的结果表明，硝酸盐吸收诱导的根际碱化通过 H O 依赖的根氧化能力和苯丙烷代谢途径导致水稻缺铁。
