Fotopoulos Vasileios, Sanmartin Maite, Kanellis Angelos K
Group of Biotechnology of Pharmaceutical Plants, Laboratory of Pharmacognosy, Department of Pharmaceutical Sciences, Aristotle University of Thessaloniki, 541 24 Thessaloniki, Greece.
J Exp Bot. 2006;57(14):3933-43. doi: 10.1093/jxb/erl147. Epub 2006 Sep 22.
Ascorbate oxidase (AO) is a cell wall-localized enzyme that uses oxygen to catalyse the oxidation of ascorbate (AA) to the unstable radical monodehydroascorbate (MDHA) which rapidly disproportionates to yield dehydroascorbate (DHA) and AA, and thus contributes to the regulation of the AA redox state. Here, it is reported that in vivo lowering of the apoplast AA redox state, through increased AO expression in transgenic tobacco (Nicotiana tabacum L. cv. Xanthi), exerts no effects on the expression levels of genes involved in AA recycling under normal growth conditions, but plants display enhanced sensitivity to various oxidative stress-promoting agents. RNA blot analyses suggest that this response correlates with a general suppression of the plant's antioxidative metabolism as demonstrated by lower expression levels of AA recycling genes. Furthermore, studies using Botrytis cinerea reveal that transgenic plants exhibit increased sensitivity to fungal infection, although the response is not accompanied by a similar suppression of AA recycling gene expression. Our current findings, combined with previous studies which showed the contribution of AO in the regulation of AA redox state, suggest that the reduction in the AA redox state in the leaf apoplast of these transgenic plants results in shifts in their capacity to withstand oxidative stress imposed by agents imposing oxidative stress.
抗坏血酸氧化酶（AO）是一种定位于细胞壁的酶，它利用氧气催化抗坏血酸（AA）氧化为不稳定的自由基单脱氢抗坏血酸（MDHA），MDHA迅速歧化生成脱氢抗坏血酸（DHA）和AA，从而有助于调节AA的氧化还原状态。在此，有报道称，在转基因烟草（Nicotiana tabacum L. cv. Xanthi）中通过增加AO表达来降低质外体AA氧化还原状态，在正常生长条件下对参与AA循环的基因表达水平没有影响，但植株对各种促进氧化应激的试剂表现出增强的敏感性。RNA印迹分析表明，这种反应与植物抗氧化代谢的普遍抑制相关，这表现为AA循环基因的表达水平较低。此外，使用灰葡萄孢进行的研究表明，转基因植株对真菌感染表现出更高的敏感性，尽管这种反应并没有伴随着AA循环基因表达的类似抑制。我们目前的研究结果，结合先前显示AO在调节AA氧化还原状态中作用的研究，表明这些转基因植物叶片质外体中AA氧化还原状态的降低导致它们抵御由施加氧化应激的试剂所造成的氧化应激能力发生变化。
