Dehydroascorbate Reductases and Glutathione Set a Threshold for High-Light?Induced Ascorbate Accumulation
Dehydroascorbate Reductases and Glutathione Set a Threshold for High-Light?Induced Ascorbate Accumulation
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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阈值
DOI：
10.1104/pp.19.01556
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发表时间：
2020
期刊：
影响因子：
7.4
通讯作者：
Maruta Takanori
中科院分区：
文献类型：
--
作者：
Terai Yusuke;Ueno Hiromi;Ogawa Takahisa;Sawa Yoshihiro;Miyagi Atsuko;Kawai-Yamada Maki;Ishikawa Takahiro;Maruta Takanori
植物需要高浓度的抗坏血酸作为在逆境条件下生存的氧化还原缓冲，例如强光。脱氢抗坏血酸还原酶(DHARs)是一种利用还原型谷胱甘肽(GSH)作为电子供体催化DHA还原为抗坏血酸的酶，允许抗坏血酸快速循环。然而，最近的一项研究使用了一个缺失所有这三个DHAR基因的拟南芥(Arabiopsis Thaliana)三重突变体(这里称为∆DHAR)，没有发现它们在氧化胁迫下抗坏血酸循环中作用的证据。为了进一步研究DHARs的功能，我们建立了∆达哈尔拟南芥植株以及一个将∆达哈尔与导致抗坏血酸缺乏的附加vtc2突变相结合的四重突变系。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在强光下对抗坏血酸的充分积累有不可忽视的影响，但当抗坏血酸浓度在低到中等时，它们是可有可无的。因为谷胱甘肽本身可以非酶作用地降低DHA，所以我们使用了pad2突变体，它含有野生型谷胱甘肽水平的30%的∼。在强光下，pad2突变体在野生型水平上积累抗坏血酸；然而，当pad2突变体与∆dhar结合时，几乎完全抑制了依赖强光的抗坏血酸积累。抗坏血酸缺乏积累与抗坏血酸降解产物苏氨酸的显著增加相一致。这些发现表明，在∆DharPad2植物中，抗坏血酸的循环能力是有限的，DHAR活性和谷胱甘肽含量都为高光诱导的抗坏血酸积累设定了一个阈值。
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 threeDHARgenes (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 ∆dharArabidopsis plants as well as a quadruple mutant line combining ∆dharwith an additionalvtc2mutation 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 thepad2mutant that contains ∼30% of the wild-type GSH level. Thepad2mutant accumulated ascorbate at a wild-type level under high light; however, when thepad2mutation 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 pad2plants, and that both DHAR activity and GSH content set a threshold for high-light–induced ascorbate accumulation.