The accumulation of iron (Fe) in the apical meristem is considered as a critical factor involved in limiting the elongation of roots under low phosphate (Pi) conditions. Furthermore, the antagonism between Fe and Pi largely affects the effective utilization of Fe. Although the lack of Pi serves to increase the effectiveness of Fe in rice under both Fe-sufficient and Fe-deficient conditions, the underlying physiological mechanism governing this phenomenon is still unclear. In this study, we found that low Pi alleviated the Fe-deficiency phenotype in apples. Additionally, low Pi treatments increased ferric-chelated reductase (FCR) activity in the rhizosphere, promoted proton exocytosis, and enhanced the Fe concentration in both the roots and shoots. In contrast, high Pi treatments inhibited this process. Under conditions of low Pi, malate and citrate exudation from apple roots occurred under both Fe-sufficient and Fe-deficient conditions. In addition, treatment with 0.5 mM malate and citrate effectively alleviated the Fe and Pi deficiencies. Taken together, these data support the conclusion that a low Pi supply promotes organic acids exudation and enhances Fe absorption during Fe deficiency in apples.

中文翻译：

---

磷酸盐调节苹果酸/柠檬酸盐介导的苹果铁吸收和运输

铁（Fe）在顶端分生组织中的积累被认为是在低磷酸盐（Pi）条件下限制根伸长的关键因素。此外，Fe和Pi之间的拮抗作用在很大程度上影响了Fe的有效利用。尽管在 Fe 充足和 Fe 缺乏的条件下，缺乏 Pi 有助于提高水稻中 Fe 的有效性，但控制这种现象的潜在生理机制仍不清楚。在这项研究中，我们发现低 Pi 减轻了苹果的缺铁表型。此外，低磷处理增加了根际中铁螯合还原酶 (FCR) 的活性，促进了质子胞吐作用，并提高了根和芽中的 Fe 浓度。相比之下，高 Pi 处理抑制了这个过程。在低 Pi 条件下，在铁充足和铁缺乏的条件下，苹果根部的苹果酸和柠檬酸盐渗出物发生。此外，用 0.5 mM 苹果酸盐和柠檬酸盐处理可有效缓解 Fe 和 Pi 的缺乏。综上所述，这些数据支持以下结论：在苹果缺铁期间，低 Pi 供应促进有机酸渗出并增强铁吸收。