甘藷傷害後一氧化氮促進超氧歧異酶以及抗壞血酸過氧化物酶並抑制細胞死亡

Abstract

無論是環境或是生物因子所造成的傷害，都可以使植物產生防禦機制。在前人研究中指出，物理性的傷害可以使植物產生一氧化氮 (NO) 以及過氧化氫 (H2O2)。因此，在此篇研究中，我們將專注於討論甘藷 (Ipomoea batatas cv. Tainung 57) 受到傷害後，NO與H2O2的功能，以及其交互作用。物理性傷害會使得植物細胞產生細胞死亡，預先處理NO供應劑之後，則會使此細胞死亡的現象降低，然而預先處理NO清除劑則是使此現象更加劇烈。分析植物體內傷害後產生的H2O2含量，也可以發現預先處理NO供應劑之後H2O2含量較低，而預先處理NO清除劑則是會提高H2O2含量。因此我們認為NO可以調控植物體內，傷害後所產生的H2O2含量，達到調控細胞死亡的功能。我們利用蛋白質二維電泳，分離出NO誘導的蛋白質：Copper/Zinc superoxide dismutases (CuZnSODs)，CuZnSODs屬於抗氧化的蛋白質。並且也發現CuZnSOD和 ascorbate peroxidase (APX) 兩個抗氧化蛋白質活性，也同樣會受到NO的誘導而增加。除此之外，傷害誘導CuZnSOD和APX的基因表現，必須透過NO作為媒介，並且NO的訊息傳遞也需要透過cGMP來達成。NO誘導APX基因表現的訊息傳遞，還需要透過鈣離子與NADPH oxidase來完成。綜合實驗的結果，當植物受到傷害後會產生細胞死亡，然而同時間傷害也可以產生NO，此NO的生成可以透過cGMP、鈣離子以及NADPH oxidase所產生的H2O2，進而誘導CuZnSOD和APX的基因表現，以代謝過多的過氧化物，保護植物不至於引發過多的細胞死亡。

Wounding caused by rain, wind, and pathogen may cause plants to onset defense response. Previous studies indicated that mechanical wounding stimulates plants to generate nitric oxide (NO) and hydrogen peroxide (H2O2). In this study, the functions of NO and H2O2 after wounding in sweet potato (Ipomoea batatas cv. Tainung 57) was further analyzed. Mechanical wounding damaged cells to become necrosis, but the presence of NO donor and NO scavenger might reduce and enhance the cell death caused by wounding, respectively. The amount of H2O2 induced by wounding was also decreased and increased when plants were incubated in NO donor and NO scavenger, individually. These results may indicate that NO regulates H2O2 generation to affect cell death. NO-induced proteins were further isolated from two-dimensional electrophoresis, and were identified to be Copper/Zinc superoxide dismutases (CuZnSODs). The activities of CuZnSODs and ascorbate peroxidase (APX) could be enhanced by NO. In addition, the expression of CuZnSOD and APX was induced by wounding via NO, and their expression was further stimulated by NO through the generation of cGMP. The influx of calcium ions and the activity of NADPH oxidase were also involved in the NO signal transduction pathway inducing the expression of APX. Collectively, when plants were wounded the generation of H2O2 might trigger cell death. Meanwhile, the production of NO induced by wounding stimulated signal transducers, including cGMP, calcium ions, and H2O2, to activate CuZnSOD and APX , which further decreased H2O2 level and reduced the cell death caused by wounding.