PDF(Pubmed)
Abstract：
Ascorbate (vitamin C) is one of the most abundant primary metabolites in plants. Its complex chemistry enables it to function as an antioxidant, as a free radical scavenger, and as a reductant for iron and copper. Ascorbate biosynthesis occurs via the mannose/l-galactose pathway in green plants, and the evidence for this pathway being the major route is reviewed. Ascorbate accumulation is leaves is responsive to light, reflecting various roles in photoprotection. GDP-l-galactose phosphorylase (GGP) is the first dedicated step in the pathway and is important in controlling ascorbate synthesis. Its expression is determined by a combination of transcription and translation. Translation is controlled by an upstream open reading frame (uORF) which blocks translation of the main GGP-coding sequence, possibly in an ascorbate-dependent manner. GGP associates with a PAS-LOV protein, inhibiting its activity, and dissociation is induced by blue light. While low ascorbate mutants are susceptible to oxidative stress, they grow nearly normally. In contrast, mutants lacking ascorbate do not grow unless rescued by supplementation. Further research should investigate possible basal functions of ascorbate in severely deficient plants involving prevention of iron overoxidation in 2-oxoglutarate-dependent dioxygenases and iron mobilization during seed development and germination.
摘要：
抗坏血酸（维生素C）是植物中最丰富的初级代谢产物之一。其复杂的化学性质使其能够起到抗氧化剂的作用，自由基清除剂和铁和铜的还原剂。在绿色植物中通过甘露糖/L-半乳糖途径发生抗坏血酸生物合成，并回顾了该途径是主要途径的证据。抗坏血酸的积累是叶子对光的反应，反映光保护的各种作用。GDP-L-半乳糖磷酸化酶（GGP）是该途径中的第一个专用步骤，在控制抗坏血酸合成中很重要。其表达由转录和翻译的组合决定。翻译由上游开放阅读框（uORF）控制，该开放阅读框阻止主要GGP编码序列的翻译，可能以依赖抗坏血酸的方式。GGP与PAS-LOV蛋白结合，抑制其活性和解离是由蓝光诱导。虽然低抗坏血酸突变体易受氧化应激，它们几乎正常生长。相比之下,缺乏抗坏血酸的突变体不会生长，除非通过补充来拯救。进一步的研究应研究抗坏血酸在严重缺乏植物中的可能基础功能，包括防止2-酮戊二酸依赖性双加氧酶中铁的过度氧化和种子发育和发芽过程中的铁动员。
