Iron (Fe) is an essential element for plant growth, development and metabolism. Due to its lack of solubility and low bioavailability in soil, Fe levels are usually far below the optimum amount for most plants' growth and development. In apple production, excessive use of nitrogen fertilizer may cause iron chlorosis symptoms in the newly growing leaves, but the regulatory mechanisms underlying this phenomenon are unclear. In this study, low nitrate (NO₃⁻, LN) application alleviated the symptoms of Fe deficiency and promoted lower rhizosphere pH, which was beneficial for root Fe acquisition. At the same time, LN treatment increased citrate and abscisic acid accumulation in roots, which promoted Fe transport from root to shoot and maintained Fe homeostasis. Moreover, qRT-PCR analysis showed that nitrate application caused differential expression of genes related to Fe uptake and transport, as well as transcriptional regulators. In summary, our data reveal that low nitrate alleviated Fe deficiency through multiple pathways, demonstrating a new option for minimizing Fe deficiency by regulating the balance between nutrients.

中文翻译：

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低硝酸盐通过调节苹果铁稳态缓解铁缺乏症

铁（Fe）是植物生长、发育和代谢的必需元素。由于其在土壤中缺乏溶解性和低生物利用度，铁含量通常远低于大多数植物生长发育的最佳量。在苹果生产中，过量使用氮肥可能会导致新生叶片出现铁质萎黄症状，但这种现象背后的调控机制尚不清楚。在本研究中，低硝酸盐（NO ₃ ^-, LN) 的施用减轻了缺铁症状并促进了较低的根际 pH 值，这有利于根系铁的获取。同时，LN 处理增加了根中柠檬酸盐和脱落酸的积累，促进了 Fe 从根向地上部的转运，维持了 Fe 的稳态。此外，qRT-PCR 分析表明，施用硝酸盐会导致与铁摄取和转运相关的基因以及转录调节因子的差异表达。总之，我们的数据表明，低硝酸盐通过多种途径缓解了铁缺乏症，展示了一种通过调节营养素之间的平衡来最大限度减少铁缺乏症的新选择。