Hamada Tamami, Yamamoto Kojiro, Hamada Akane, Maruta Takanori
Graduate School of Natural Science and Technology, Shimane University, 1060 Nishikawatsu, Matsue, Shimane 690-8504, Japan.
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.
Plant Sci. 2025 Oct;359:112608. doi: 10.1016/j.plantsci.2025.112608. Epub 2025 Jun 11.
Ascorbate is a key antioxidant that protects plant cells from oxidative damage. While plants actively synthesize ascorbate during the day, its degradation becomes prominent under prolonged dark conditions. Since ascorbate degradation begins with its oxidized form, dehydroascorbate (DHA), this process inherently requires ascorbate oxidation. However, the molecular mechanisms underlying dark-induced ascorbate oxidation and subsequent degradation remain unclear. In this study, we investigated the role of intracellular and extracellular ascorbate redox regulation in controlling this process. Using Arabidopsis knockout mutants for key enzymes involved in ascorbate oxidation and recycling, including ascorbate peroxidase (APX), monodehydroascorbate reductase (MDAR), dehydroascorbate reductase (DHAR), and ascorbate oxidase (AO), as well as NADPH oxidases (rbohD and rbohF), we found that none of these enzymes significantly influenced the dark-induced decrease in ascorbate levels. Notably, ascorbate levels decreased similarly in newly generated multiple mutants, including a quintuple mutant (∆dhar pad2 mdar5), which has severely impaired ascorbate recycling capacity, and the ao2 rbohD double mutant, which is strongly expected to exhibit a highly altered apoplastic redox state. Furthermore, we examined the potential involvement of senescence signaling, including ORESARA1 and ethylene signaling components, but found no evidence for their contribution. These findings indicate that the dark-induced decrease in ascorbate levels is not governed by conventional pathways for ascorbate oxidation and recycling or senescence signaling processes, suggesting an unidentified regulatory mechanism.
抗坏血酸盐是一种关键的抗氧化剂，可保护植物细胞免受氧化损伤。虽然植物在白天会积极合成抗坏血酸盐，但在长时间黑暗条件下其降解会变得显著。由于抗坏血酸盐的降解始于其氧化形式脱氢抗坏血酸盐（DHA），因此这个过程本质上需要抗坏血酸盐的氧化。然而，黑暗诱导的抗坏血酸盐氧化及随后降解的分子机制仍不清楚。在本研究中，我们调查了细胞内和细胞外抗坏血酸盐氧化还原调节在控制这一过程中的作用。利用拟南芥中参与抗坏血酸盐氧化和循环的关键酶的敲除突变体，包括抗坏血酸过氧化物酶（APX）、单脱氢抗坏血酸还原酶（MDAR）、脱氢抗坏血酸还原酶（DHAR）、抗坏血酸氧化酶（AO）以及NADPH氧化酶（rbohD和rbohF），我们发现这些酶均未显著影响黑暗诱导的抗坏血酸盐水平下降。值得注意的是，在新产生的多个突变体中，抗坏血酸盐水平的下降情况相似，包括抗坏血酸盐循环能力严重受损的五重突变体（∆dhar pad2 mdar5）以及强烈预期会表现出高度改变的质外体氧化还原状态的ao2 rbohD双突变体。此外，我们研究了衰老信号传导（包括ORE-SARA1和乙烯信号成分）的潜在参与情况，但未发现它们发挥作用的证据。这些发现表明，黑暗诱导的抗坏血酸盐水平下降不受抗坏血酸盐氧化和循环的传统途径或衰老信号传导过程的控制，这表明存在一种未知的调节机制。
