Ascorbic Acid in Plants: Biosynthesis and Function
Ascorbic Acid in Plants: Biosynthesis and Function
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DOI：
10.1080/07352680091139231
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发表时间：
2000-07
影响因子：
6.9
通讯作者：
N. Smirnoff;Glen L. Wheeler
中科院分区：
文献类型：
--
作者：
N. Smirnoff;Glen L. Wheeler
抗坏血酸(维生素C)是植物中含量丰富的成分。它在叶绿体中的浓度超过20mm，存在于包括细胞壁在内的所有细胞室中。它在光合作用中作为一种酶辅助因子（包括乙烯、赤霉素和花青素的合成）和控制细胞生长。通过gdp -甘露糖、gdp -l -半乳糖、l -半乳糖和l -半乳糖-1,4-内酯的生物合成途径最近才被提出，并得到来自拟南芥抗坏血酸缺乏的vtc1突变体的分子遗传学证据的支持。其他途径通过醛酸可以提供少量的抗坏血酸来源。抗坏血酸，至少在某些物种中，是酒石酸盐和草酸盐的前体。它在光合作用中起主要作用，参与梅勒过氧化物酶与抗坏血酸过氧化物酶的反应，调节光合电子载体的氧化还原状态，并作为紫黄素去环氧酶的辅助因子，紫黄素去环氧酶参与叶黄素循环介导的光保护。一些vtc突变体对臭氧和UV-B辐射的超敏反应，抗坏血酸过氧化物酶对（光）氧化应激的快速反应，以及抗坏血酸过氧化物酶活性改变的转基因植物的特性，都支持抗坏血酸具有重要的抗氧化作用。与细胞生长有关，抗坏血酸是脯氨酸羟化酶的辅助因子，该酶翻译后羟化细胞壁富含脯氨酸的糖蛋白中的脯氨酸残基，这是细胞分裂和扩增所必需的。此外，细胞壁的高抗坏血酸氧化酶活性与细胞快速扩张的区域有关。这是否是一种因果关系，如果是，其机制是什么，还有待确定。生物合成途径的鉴定现在为操纵植物中的抗坏血酸生物合成开辟了道路，并且，与vtc突变体一起，这将有助于更深入地了解这种多面分子的功能。
Ascorbic acid (vitamin C) is an abundant component of plants. It reaches a concentration of over 20 mM in chloroplasts and occurs in all cell compartments, including the cell wall. It has proposed functions in photosynthesis as an enzyme cofactor (including synthesis of ethylene, gibberellins and anthocyanins) and in control of cell growth. A biosynthetic pathway via GDP-mannose, GDP-L-galactose, L-galactose, and L-galactono-1,4-lactone has been proposed only recently and is supported by molecular genetic evidence from the ascorbate deficient vtc1 mutant of Arabidopsis thaliana. Other pathways via uronic acids could provide minor sources of ascorbate. Ascorbate, at least in some species, is a precursor of tartrate and oxalate. It has a major role in photosynthesis, acting in the Mehler peroxidase reaction with ascorbate peroxidase to regulate the redox state of photosynthetic electron carriers and as a cofactor for violaxanthin de-epoxidase, an enzyme involved in xanthophyll cyclemediated photoprotection. The hypersensitivity of some of the vtc mutants to ozone and UV-B radiation, the rapid response of ascorbate peroxidase expression to (photo)oxidative stress, and the properties of transgenic plants with altered ascorbate peroxidase activity all support an important antioxidative role for ascorbate. In relation to cell growth, ascorbate is a cofactor for prolyl hydroxylase that posttranslationally hydroxylates pro line residues in cell wall hydroxyproline-rich glycoproteins required for cell division and expansion. Additionally, high ascorbate oxidase activity in the cell wall is correlated with areas of rapid cell expansion. It remains to be determined if this is a causal relationship and, if so, what is the mechanism. Identification of the biosynthetic pathway now opens the way to manipulating ascorbate biosynthesis in plants, and, along with the vtc mutants, this should contribute to a deeper understanding of the proposed functions of this multifacetted molecule.