Dehydroascorbate Reductases and Glutathione Set a Threshold for High-Light-Induced Ascorbate Accumulation.,Plant Physiology

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Dehydroascorbate Reductases and Glutathione Set a Threshold for High-Light-Induced Ascorbate Accumulation.
Plant Physiology ( IF 6.5 ) Pub Date : 2020-03-23 , DOI: 10.1104/pp.19.01556
Yusuke Terai ₁ , Hiromi Ueno ₂ , Takahisa Ogawa _{1,

2,

3} , Yoshihiro Sawa ₁ , Atsuko Miyagi ₄ , Maki Kawai-Yamada ₄ , Takahiro Ishikawa _{1,

2,

3} , Takanori Maruta _{2,

3,

5}

Affiliation

Plants require a high concentration of ascorbate as a redox buffer for survival under stress conditions, such as high light. Dehydroascorbate reductases (DHARs) are enzymes that catalyze the reduction of DHA to ascorbate using reduced glutathione (GSH) as an electron donor, allowing rapid ascorbate recycling. However, a recent study using an Arabidopsis (Arabidopsis thaliana) triple mutant lacking all three DHAR genes (herein called ∆dhar) did not find evidence for their role in ascorbate recycling under oxidative stress. To further study the function of DHARs, we generated ∆dhar Arabidopsis plants as well as a quadruple mutant line combining ∆dhar with an additional vtc2 mutation that causes ascorbate deficiency. Measurements of ascorbate in these mutants under low- or high-light conditions indicated that DHARs have a nonnegligible impact on full ascorbate accumulation under high light, but that they are dispensable when ascorbate concentrations are low to moderate. Because GSH itself can reduce DHA nonenzymatically, we used the pad2 mutant that contains ∼30% of the wild-type GSH level. The pad2 mutant accumulated ascorbate at a wild-type level under high light; however, when the pad2 mutation was combined with ∆dhar, there was near-complete inhibition of high-light-dependent ascorbate accumulation. The lack of ascorbate accumulation was consistent with a marked increase in the ascorbate degradation product threonate. These findings indicate that ascorbate recycling capacity is limited in ∆dhar pad2 plants, and that both DHAR activity and GSH content set a threshold for high-light-induced ascorbate accumulation.

中文翻译：

脱氢抗坏血酸还原酶和谷胱甘肽为高光诱导的抗坏血酸积累设定了阈值。

植物需要高浓度的抗坏血酸作为氧化还原缓冲液，才能在强光等胁迫条件下生存。脱氢抗坏血酸还原酶（DHARs）是使用还原型谷胱甘肽（GSH）作为电子供体，催化DHA还原为抗坏血酸的酶，可快速回收抗坏血酸。但是，最近的一项研究使用缺少所有三个DHAR基因（在此称为Δdhar）的拟南芥（Arabidopsis thaliana）三重突变体，没有发现它们在氧化应激下抗坏血酸循环中的作用的证据。为了进一步研究DHAR的功能，我们生成了Δdhar拟南芥植物以及结合了ddhar和导致抗坏血酸缺乏的其他vtc2突变的四重突变株系。在弱光或强光条件下对这些突变体中抗坏血酸的测量表明，DHARs在强光下对完全抗坏血酸的积累具有不可忽略的影响，但是当抗坏血酸浓度从低到中等时，它们是必不可少的。因为GSH本身可以非酶促地还原DHA，所以我们使用了含有约30％野生型GSH水平的pad2突变体。pad2突变体在强光下以野生型水平积累抗坏血酸。但是，当pad2突变与ddhar结合使用时，几乎完全抑制了高光依赖性抗坏血酸的积累。缺乏抗坏血酸的积累与抗坏血酸降解产物苏氨酸的显着增加是一致的。这些发现表明，Δdharpad2工厂的抗坏血酸回收能力有限，

更新日期：2020-05-01

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