Calcium oxalate (CaOx) crystals in plants are formed in crystal idioblasts cells and have specific geometric shapes. Their proposed functions include calcium homeostasis and carbon source, among others. Amaranth is a plant that presents high tolerance to abiotic stresses and accumulates considerable amounts of CaOx crystals; however, few studies have focused on characterizing the crystals ultrastructure and none is related to identifying proteins bound to them. This information is of great interest to understand the mechanisms related to CaOx crystal formation and to support their proposed functions. Thus, this work aimed to characterize CaOx crystals in amaranth leaves. Crystals were purified and the proteins bound to them were isolated and identified by nLC–MS/MS. Leaf sections were analyzed by light and electron microscopy. The identified proteins were related to the chloroplast such as ATPb synthase, RuBisCO large subunit, and cell wall-related proteins, which were validated by immunohistochemistry and immunogold labeling. In addition, it was observed that CaOx crystal idioblasts were formed from parenchyma cells associated with mesophyll and veins, in which the thylakoid membranes of degraded chloroplasts turned into crystal chambers. These results significantly advance our understanding of the mechanisms of CaOx crystal formation and the potential function as an alternative carbon source in leaves.

中文翻译：

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苋菜草酸钙晶体与叶绿体结构和蛋白质有关

植物中的草酸钙 (CaOx) 晶体在晶体成岩细胞中形成，具有特定的几何形状。他们提出的功能包括钙稳态和碳源等。苋菜是一种对非生物胁迫具有高度耐受性并积累大量 CaOx 晶体的植物；然而，很少有研究专注于表征晶体超微结构，并且没有一项与识别与其结合的蛋白质有关。该信息对于了解与 CaOx 晶体形成相关的机制并支持其提出的功能具有重要意义。因此，这项工作旨在表征苋菜叶中的 CaOx 晶体。纯化晶体并通过 nLC-MS/MS 分离和鉴定与其结合的蛋白质。通过光学和电子显微镜分析叶切片。鉴定的蛋白质与叶绿体有关，如 ATPb 合酶、RuBisCO 大亚基和细胞壁相关蛋白，并通过免疫组织化学和免疫金标记验证。此外，观察到CaOx晶体成体细胞由与叶肉和静脉相关的薄壁细胞形成，其中降解的叶绿体的类囊体膜变成晶体室。这些结果显着促进了我们对 CaOx 晶体形成机制和作为叶子中替代碳源的潜在功能的理解。观察到CaOx晶体成体细胞由与叶肉和静脉相关的薄壁细胞形成，其中降解的叶绿体的类囊体膜变成晶体室。这些结果显着促进了我们对 CaOx 晶体形成机制和作为叶子中替代碳源的潜在功能的理解。观察到CaOx晶体成体细胞由与叶肉和静脉相关的薄壁细胞形成，其中降解的叶绿体的类囊体膜变成晶体室。这些结果显着促进了我们对 CaOx 晶体形成机制和作为叶子中替代碳源的潜在功能的理解。