Department of Biology, Faculty of Arts and Sciences, Rize University, 53100, Rize, Turkey.
Biol Res. 2009;42(3):315-26. Epub 2009 Nov 2.
The ascorbate-glutathione (ASC-GSH) cycle has an important role in defensive processes against oxidative damage generated by drought stress. In this study, the changes that take place in apoplastic and symplastic ASC-GSH cycle enzymes of the leaf and petiole were investigated under drought stress causing leaf rolling in Ctenanthe setosa (Rose.) Eichler (Marantaceae). Apoplastic and symplastic extractions of leaf and petiole were performed at different visual leaf rolling scores from 1 to 4 (1 is unrolled, 4 is tightly rolled and the others are intermediate forms). Glutathione reductase (GR), a key enzyme in the GSH regeneration cycle, and ascorbate (ASC) were present in apoplastic spaces of the leaf and petiole, whereas dehydroascorbate reductase (DHAR), which uses glutathione as reductant, monodehydroascorbate reductase (MDHAR), which uses NAD(P)H as reductant, and glutathione were absent. GR, DHAR and MDHAR activities increased in the symplastic and apoplastic areas of the leaf. Apoplastic and symplastic ASC and dehydroascorbate (DHA), the oxidized form of ascorbate, rose at all scores except score 4 of symplastic ASC in the leaf. On the other hand, while reduced glutathione (GSH) content was enhanced, oxidized glutathione (GSSG) content decreased in the leaf during rolling. As for the petiole, GR activity increased in the apoplastic area but decreased in the symplastic area. DHAR and MDHAR activities increased throughout all scores, but decreased to the score 1 level at score 4. The ASC content of the apoplast increased during leaf rolling. Conversely, symplastic ASC content increased at score 2, however decreased at the later scores. While the apoplastic DHA content declined, symplastic DHA rose at score 2, but later was down to the level of score 1. While GSH content enhanced during leaf rolling, GSSG content did not change except at score 2. As well, there were good correlations between leaf rolling and ASC-GSH cycle enzyme activities in the leaf (GR and DHAR) and leaf rolling and GSSG. These results showed that in apoplastic and symplastic areas, ASC-GSH cycle enzymes leading ROS detoxification may have a role in controlling leaf rolling.
抗坏血酸-谷胱甘肽 (ASC-GSH) 循环在防御由干旱胁迫引起的氧化损伤方面具有重要作用。在这项研究中，研究了在引起 Ctenanthe setosa (Rose.) Eichler（马兰科）叶片卷曲的干旱胁迫下，叶片和叶柄的质外体和共质体 ASC-GSH 循环酶发生的变化。在从 1 到 4 的不同视觉叶片卷曲评分下（1 是未卷曲，4 是紧紧卷曲，其他是中间形式），对叶片和叶柄进行质外体和共质体提取。谷胱甘肽还原酶 (GR)，GSH 再生循环中的关键酶，存在于叶片和叶柄的质外体空间中，而使用谷胱甘肽作为还原剂的脱氢抗坏血酸还原酶 (DHAR)、使用 NAD(P)H 作为还原剂的单脱氢抗坏血酸还原酶 (MDHAR) 和谷胱甘肽则不存在。GR、DHAR 和 MDHAR 活性在叶片的共质体和质外体区域增加。除了叶片的共质体 ASC 评分 4 外，叶片的质外体和共质体 ASC 和脱氢抗坏血酸 (DHA)，即 ASC 的氧化形式，在所有评分中均升高。另一方面，虽然还原型谷胱甘肽 (GSH) 含量增加，但在叶片卷曲过程中氧化型谷胱甘肽 (GSSG) 含量减少。至于叶柄，GR 活性在质外体区域增加，但在共质体区域减少。DHAR 和 MDHAR 活性在所有评分中均增加，但在评分 4 时降至评分 1 水平。叶片卷曲过程中质外体 ASC 含量增加。相反，共质体 ASC 含量在评分 2 时增加，但后来下降到评分 1 的水平。虽然质外体 DHA 含量下降，但共质体 DHA 在评分 2 时上升，但后来降至评分 1 的水平。叶片卷曲过程中，GSH 含量增加，GSSG 含量不变，除了评分 2。同样，叶片卷曲与叶片质外体和共质体 ASC-GSH 循环酶活性（GR 和 DHAR）以及叶片卷曲与 GSSG 之间存在良好的相关性。这些结果表明，在质外体和共质体区域中，可能参与控制叶片卷曲的抗坏血酸-谷胱甘肽 (ASC-GSH) 循环酶在 ROS 解毒中起作用。
