Shigeoka Shigeru, Ishikawa Takahiro, Tamoi Masahiro, Miyagawa Yoshiko, Takeda Toru, Yabuta Yukinori, Yoshimura Kazuya
Department of Food and Nutrition, Faculty of Agriculture, Kinki University, Nakamachi, Nara 631-8505, Japan.
J Exp Bot. 2002 May;53(372):1305-19.
Even under optimal conditions, many metabolic processes, including the chloroplastic, mitochondrial, and plasma membrane-linked electron transport systems of higher plants, produce active oxygen species (AOS). Furthermore, the imposition of biotic and abiotic stress conditions can give rise to excess concentrations of AOS, resulting in oxidative damage at the cellular level. Therefore, antioxidants and antioxidant enzymes function to interrupt the cascades of uncontrolled oxidation in each organelle. Ascorbate peroxidase (APX) exists as isoenzymes and plays an important role in the metabolism of H(2)O(2) in higher plants. APX is also found in eukaryotic algae. The characterization of APX isoenzymes and the sequence analysis of their clones have led to a number of investigations that have yielded interesting and novel information on these enzymes. Interestingly, APX isoenzymes of chloroplasts in higher plants are encoded by only one gene, and their mRNAs are generated by alternative splicing of the gene's two 3'-terminal exons. Manipulation of the expression of the enzymes involved in the AOS-scavenging systems by gene-transfer technology has provided a powerful tool for increasing the present understanding of the potential of the defence network against oxidative damage caused by environmental stresses. Transgenic plants expressing E. coli catalase to chloroplasts with increased tolerance to oxidative stress indicate that AOS-scavenging enzymes, especially chloroplastic APX isoenzymes are sensitive under oxidative stress conditions. It is clear that a high level of endogenous ascorbate is essential effectively to maintain the antioxidant system that protects plants from oxidative damage due to biotic and abiotic stresses.
即使在最佳条件下，许多代谢过程，包括高等植物的叶绿体、线粒体以及与质膜相连的电子传递系统，都会产生活性氧（AOS）。此外，生物和非生物胁迫条件的施加会导致AOS浓度过高，从而在细胞水平上造成氧化损伤。因此，抗氧化剂和抗氧化酶的作用是中断每个细胞器中不受控制的氧化级联反应。抗坏血酸过氧化物酶（APX）以同工酶的形式存在，在高等植物H₂O₂的代谢中起重要作用。在真核藻类中也发现了APX。APX同工酶的特性及其克隆的序列分析引发了许多研究，这些研究产生了关于这些酶的有趣且新颖的信息。有趣的是，高等植物叶绿体中的APX同工酶仅由一个基因编码，其mRNA是由该基因两个3'末端外显子的可变剪接产生的。通过基因转移技术操纵参与AOS清除系统的酶的表达，为增进目前对防御网络抵御环境胁迫引起的氧化损伤潜力的理解提供了一个有力工具。向叶绿体中表达大肠杆菌过氧化氢酶的转基因植物对氧化胁迫的耐受性增强，这表明AOS清除酶，尤其是叶绿体APX同工酶在氧化胁迫条件下很敏感。显然，高水平的内源性抗坏血酸对于有效维持保护植物免受生物和非生物胁迫引起的氧化损伤的抗氧化系统至关重要。
