Graduate School of Natural Science and Technology, Shimane University, 1060 Nishikawatsu, Matsue, Shimane 690-8504, Japan.
Bioresource and Life Sciences, The United Graduate School of Agricultural Sciences, Tottori University, 4-101 Koyama-Minami, Tottori, Tottori 680-8553, Japan.
J Exp Bot. 2024 May 3;75(9):2664-2681. doi: 10.1093/jxb/erae062.
Plants accumulate high concentrations of ascorbate, commonly in their leaves, as a redox buffer. While ascorbate levels have increased during plant evolution, the mechanisms behind this phenomenon are unclear. Moreover, has the increase in ascorbate concentration been achieved without imposing any detrimental effects on the plants? In this review, we focus on potential transitions in two regulatory mechanisms related to ascorbate biosynthesis and the availability of cellular dehydroascorbate (DHA) during plant evolution. The first transition might be that the trigger for the transcriptional induction of VTC2, which encodes the rate-limiting enzyme in ascorbate biosynthesis, has shifted from oxidative stress (in green algae) to light/photosynthesis (in land plants), probably enabling the continuous accumulation of ascorbate under illumination. This could serve as a preventive system against the unpredictable occurrence of oxidative stress. The second transition might be that DHA-degrading enzymes, which protect cells from the highly reactive DHA in green algae and mosses, have been lost in ferns or flowering plants. Instead, flowering plants may have increased glutathione concentrations to reinforce the DHA reduction capacity, possibly allowing ascorbate accumulation and avoiding the toxicity of DHA. These potential transitions may have contributed to strategies for plants' safe and effective accumulation of ascorbate.
植物会在其叶片中积累高浓度的抗坏血酸，通常作为氧化还原缓冲剂。虽然植物进化过程中抗坏血酸水平有所增加，但这一现象背后的机制尚不清楚。此外，抗坏血酸浓度的增加是否在对植物没有造成任何不利影响的情况下实现的？在这篇综述中，我们重点关注与抗坏血酸生物合成和细胞脱氢抗坏血酸（DHA）可用性相关的两个调节机制的潜在转变。第一个可能的转变是，编码抗坏血酸生物合成限速酶的 VTC2 的转录诱导的触发因素可能已经从氧化应激（在绿藻中）转变为光照/光合作用（在陆生植物中），这可能使抗坏血酸在光照下能够持续积累。这可以作为一种预防系统，防止不可预测的氧化应激发生。第二个可能的转变是，在绿藻和苔藓中保护细胞免受高反应性 DHA 侵害的 DHA 降解酶在蕨类植物或开花植物中已经丢失。相反，开花植物可能增加了谷胱甘肽浓度，以增强 DHA 的还原能力，从而可能允许抗坏血酸的积累并避免 DHA 的毒性。这些潜在的转变可能为植物安全有效地积累抗坏血酸提供了策略。
