水杨酸处理诱导采后甜瓜抗坏血酸-还原型谷胱甘肽循环代谢清除过氧化氢的作用及机制

目的：研究抗坏血酸（ascorbic acid，AsA）-还原型谷胱甘肽（reduced glutathione，GSH）循环代谢在水杨酸处理采后甜瓜诱导的过量H2O2清除过程中的作用。方法：用4 mmol/L水杨酸浸泡‘玉金香’厚皮甜瓜10 min，测定处理后果实常温贮藏过程中丙二醛（malondialdehyde，MDA）含量，分析活性氧的积累水平、超氧化物歧化酶（superoxide dismutase，SOD）和过氧化氢酶（catalase，CAT）活力，以及AsA-GSH循环过程相关酶活力及产物和底物含量。结果：水杨酸处理降低了果实MDA含量，第10天处理组MDA含量较对照组降低14.6%；显著提高了果实O2－·的产生速率和H2O2含量（P＜0.05），其中处理后第2天O2－·的产生速率高出同期对照组的1.9 倍，第6天H2O2含量高出对照组果实29.7%；提高了果实SOD活力，但抑制了CAT活力，说明H2O2的清除可能是依赖于除酶促系统外的其他系统。此外，水杨酸处理提高了果实抗坏血酸过氧化物酶、单脱氢抗坏血酸过氧化物酶、脱氢抗坏血酸还原酶和谷胱甘肽还原酶的活力，增加了AsA和氧化型谷胱甘肽的含量，降低了脱氢抗坏血酸和GSH的含量。结论：水杨酸处理诱导了厚皮甜瓜果实的氧爆，抑制了MDA产生，由水杨酸诱导产生的过量H2O2主要依靠AsA-GSH循环系统清除。

Role and Underlying Mechanism of the Ascorbic Acid-Reduced Glutathione Cycle in Scavenging Hydrogen Peroxide in Postharvest Melons Induced by Salicylic Acid

Objective:To ascertain the role of the ascorbic acid-reduced glutathione(AsA-GSH)cycle in scavenging excessive H2O2 in melons induced by salicylic acid(SA)during postharvest storage.Methods:Melon(cv.Yujinxiang)fruit were soaked in 4 mmol/L SA for 10 min,and stored at ambient temperature.Malondialdehyde(MDA)content and the accumulation level of reactive oxygen species,and the activity of superoxide dismutase(SOD)and catalase(CAT)were determined as well as enzyme activities involved in the AsA-GSH cycle and the contents of substrate and product.Results:SA treatment reduced MDA content,resulting in a 14.6%reduction in MDA content compared with the control group on day 10.SA significantly increased superoxide anion radical production rate and H2O2 content in the fruit(P<0.05).On day 2 after the treatment,the production rate of superoxide anion radical in the treated group was 1.9 times higher in than that in the control at the same time point,and H2O2 content was 29.7%higher than that in the control on day 6.The chemical increased SOD activity and inhibited CAT activity,suggesting that scavenging of H2O2 is not dependent on the enzymatic system but other systems.Moreover,SA increased the activity of ascorbate peroxidase,glutathione reductase,monodehydroascorbate peroxidase,and dehydroascorbate reductase as well as the contents of ascorbic acid and oxidized glutathione,and decreased the contents of dehydroascorbic acid and reduced glutathione.Conclusion:SA treatment promoted oxygen burst in melons and reduced MDA content.Excessive H2O2 induced by SA was scavenged mainly through the AsA-GSH cycle.