Abstract

Ascorbic acid (AA) is one of the most important antioxidants and redox-active substances of plants found in the apoplast. In the form of ascorbate anion, it can be exported to the cell wall through anion channels, where it is further oxidized to dehydroascorbic acid (DHA) and in this form is translocated back into the cytoplasm through as yet unidentified transporters. In the apoplast AA is exposed to both enzymatic and non-enzymatic oxidation, participating in the antioxidant and pro-oxidant processes: detoxification of O₃, generation of hydroxyl radicals, reduction of phenoxyl radicals, etc. The intermediate product of the AA oxidation in apoplast, monodehydroascorbic acid (MDHA), serves as an extracellular electron acceptor for a number of redox chains localized at the plasma membrane (PM). All three forms of ascorbate, AA, DHA and MDHA, can potentially be involved in the cell signalling. Released from the cell through anionic channels during PM depolarization, AA can stimulate the production of hydroxyl radicals that activate Ca²⁺-permeable channels, and thus trigger Ca²⁺-signalling. Due to the ability to generate hydroxyl radicals and reduce phenoxyl radicals, AA affects cell wall extensibility and extension growth. By reducing Fe³⁺ to a freely soluble transport form of Fe²⁺, AA is involved in iron uptake by root cells. Apoplastic AA also plays an important role in a number of other processes and is potentially a unique signal-regulatory molecule functioning in the plant cell walls.

中文翻译：

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质外体中的抗坏血酸：代谢和功能

摘要

抗坏血酸（AA）是质外体中最重要的植物抗氧化剂和氧化还原活性物质之一。它可以以抗坏血酸阴离子的形式通过阴离子通道输出到细胞壁，在此处它被进一步氧化成脱氢抗坏血酸（DHA），并以这种形式通过尚未被确定的转运蛋白重新转运回细胞质。在质外体中，AA暴露于酶促和非酶促氧化中，参与抗氧化剂和促氧化剂过程：O _3的解毒，羟基自由基的产生，苯氧基自由基的还原等。质外体中AA氧化的中间产物一氢脱氢抗坏血酸（MDHA），对于质膜（PM）上的许多氧化还原链起细胞外电子受体的作用。抗坏血酸的所有三种形式，AA，DHA和MDHA，都可能参与细胞信号传导。在PM去极化过程中，AA通过阴离子通道从细胞中释放出来，可以刺激激活Ca ²⁺渗透通道的羟基自由基的产生，从而触发Ca ²⁺信号传递。由于具有产生羟基自由基和还原苯氧基自由基的能力，AA影响细胞壁的延伸性和延伸生长。通过将Fe ³⁺还原为易溶的Fe转运形式²⁺，AA与根细胞摄取铁有关。质外性AA在许多其他过程中也起着重要作用，并且潜在地是在植物细胞壁中起作用的独特的信号调节分子。