The accumulation of NiCo following the termination of the accumulation of iron in chloroplast suggests that NiCo is not solely involved in iron uptake processes of chloroplasts. Chloroplast iron (Fe) uptake is thought to be operated by a complex containing permease in chloroplast 1 (PIC1) and nickel–cobalt transporter (NiCo) proteins, whereas the role of other Fe homeostasis-related transporters such as multiple antibiotic resistance protein 1 (MAR1) is less characterized. Although pieces of information exist on the regulation of chloroplast Fe uptake, including the effect of plant Fe homeostasis, the whole system has not been revealed in detail yet. Thus, we aimed to follow leaf development-scale changes in the chloroplast Fe uptake components PIC1, NiCo and MAR1 under deficient, optimal and supraoptimal Fe nutrition using Brassica napus as model. Fe deficiency decreased both the photosynthetic activity and the Fe content of plastids. Supraoptimal Fe nutrition caused neither Fe accumulation in chloroplasts nor any toxic effects, thus only fully saturated the need for Fe in the leaves. In parallel with the increasing Fe supply of plants and ageing of the leaves, the expression of BnPIC1 was tendentiously repressed. Though transcript and protein amount of BnNiCo tendentiously increased during leaf development, it was even markedly upregulated in ageing leaves. The relative transcript amount of BnMAR1 increased mainly in ageing leaves facing Fe deficiency. Taken together chloroplast physiology, Fe content and transcript amount data, the exclusive participation of NiCo in the chloroplast Fe uptake is not supported. Saturation of the Fe requirement of chloroplasts seems to be linked to the delay of decomposing the photosynthetic apparatus and keeping chloroplast Fe homeostasis in a rather constant status together with a supressed Fe uptake machinery.

中文翻译：

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PIC1 和 NiCo 的发育和铁营养模式不支持它们在欧洲油菜叶绿体铁转运中的相互依赖和排他性合作

在叶绿体中铁的积累终止后 NiCo 的积累表明 NiCo 不仅仅参与叶绿体的铁吸收过程。叶绿体铁 (Fe) 的吸收被认为是由含有叶绿体通透酶 1 (PIC1) 和镍钴转运蛋白 (NiCo) 蛋白的复合物控制的，而其他与 Fe 稳态相关的转运蛋白如多种抗生素抗性蛋白 1 的作用是MAR1) 的特征较少。虽然存在一些关于叶绿体铁摄取调节的信息，包括植物铁稳态的影响，但整个系统尚未详细揭示。因此，我们旨在以欧洲油菜为模型，在缺铁、最佳和超最佳铁营养条件下跟踪叶绿体铁吸收组分 PIC1、NiCo 和 MAR1 的叶片发育规模变化。Fe缺乏降低了质体的光合活性和Fe含量。超优的铁营养既不会导致叶绿体中铁的积累，也不会产生任何毒性作用，因此只能完全满足叶子对铁的需求。随着植物铁供应量的增加和叶片的老化，BnPIC1 的表达受到抑制。虽然 BnNiCo 的转录本和蛋白质含量在叶片发育过程中呈上升趋势，但在衰老叶片中甚至显着上调。BnMAR1的相对转录量主要在缺铁的老化叶片中增加。综合叶绿体生理学、Fe 含量和转录量数据，不支持 NiCo 独家参与叶绿体 Fe 摄取。