Effects of drought stress on ascorbic acid contents and activities of related metabolic enzymes in apple leaves

Chinese. 研究干旱胁迫对苹果叶片抗坏血酸（ASA）含量及其代谢相关酶活性的影响，探讨干旱胁迫与抗坏血酸-谷胱甘肽（ASA-GSH）循环的关系，为植物抗旱研究提供理论依据。以2年生嘎拉苹果(Malus domestica Borkh.)盆栽苗为试验材料，分别在轻度、中度和重度干旱胁迫及复水条件下，检测其叶片相对膜透性、丙二醛 (MDA)、过氧化氢（H2O2）和ASA-GSH循环各组分（ASA）、脱氢抗坏血酸（DHA）、GSH、氧化型谷胱甘肽（GSSG）、抗坏血酸过氧化物酶（APX）、单脱氢抗坏血酸还原酶（MDHAR）、脱氢抗坏血酸还原酶（DHAR）和谷胱甘肽还原酶（GR））含量或活性的变化。苹果叶片相对膜透性、MDA、H2O2含量随胁迫程度的加剧而上升，复水后下降。ASA-GSH循环各组分，除ASA含量在轻度干旱胁迫时上升之后略有下降、GSSG含量持续增加外，DHA和GSH含量，APX、DHAR、MDHAR和GR活性均在中度胁迫时达最大值，之后下降；ASA/DHA、GSH/GSSG比值均随胁迫程度的加剧而下降，复水后上升。随着干旱胁迫程度的加剧，苹果叶片ASA-GSH循环系统的防御能力在达到最大防御机能后下降。

English. The study was to investigate the changes in contents ofascorbic acid and activities of related metabolic enzymes in leaves of apple plants under the drought stress conditions and primary theory for the future study of drought-resistance. The experiment was carried out in the 2-year-old potted apple(Malus domestica Borkh.) plants to investigate the changes of relative membrane permeability, MDA content, hydrogen peroxide content (H2O2), the levels of components of ascorbate-glutathione (ASA-GSH) cycle including ASA, dehydroascorbate (DHA), GSH, oxidized glutathione (GSSG), ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR) and glutathione reductase (GR) under the light drought stress, moderate drought stress, severe drought stress and rewatering conditions respectively. Relative membrane permeability, MDA and H2O2 contents were gradually increased under the drought stress conditions, and decreased after rewatering. The contents of DHA and GSH and the activities of APX, DHAR, MDHAR and GR reached the highest point at the moderate drought stress, then decreased, except ASA, whose content increased at the light drought stress and then decreased slightly, and the GSSG whose content rose steadily. The ratios of ASA/DHA and GSH/GSSG decreased under the drought stress conditions, and increased after rewatering. The recovery ability of ASA-GSH cycle declined obviously after reaching the maximum with the increasing of drought stress.