The cloned ascorbate peroxidase SPAPX mitigates and delays ethephon-induced leaf senescence in sweet potato

• Main Authors: Chun-ya Liu, 劉純雅
• Other Authors: Hsien-Jung Chen
• Format: Others
• Language: zh-TW
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/w7u4g8

碩士 === 國立中山大學 === 生物科學系研究所 === 103 === Ascorbate peroxidase (APXs) is a key enzyme of glutathione-ascorbate cycle and plays an important role in the removal of reactive oxygen species(ROS)and protection against oxidative stress in plants under developmental cues and environmental stresses. With ascorbic acid as the electron donor, APXs catalyze the conversion of H2O2into H2O and O2.Ethephon, an ethylene-releasing compound, promoted leaf senescence and H2O2 elevation, which correlated with the increased level of oxidized AsA in sweet potato leaves. The APX gene and its association with ethephon mediated effects, whereas, mostly remains unclear. In this report, a full-length cDNA, SPAPX, encoding putative ascorbate peroxidase has been cloned from sweet potato leaves. Its open reading frame contains 753 nucleotides (250 amino acids) and exhibits high amino acid sequence identity (ca. 84% to 92%) with various plant APXs, including Nicotiana tabacum, Capsicum annuum, Pimpinella brachycarpa, Solanum melongena, Solanum tuberosum, Gossypium hirsutum, Glycine max, and Vigna unguiculata. Gene expression patterns showed that SPAPX was remarkably enhanced in mature leaves, then drastically reduced in partially and completely yellow senescent leaves. Ethephon significantly promoted SPAPX expression within the first 24 h, and the induction was much reduced at 48 and 72 h after treatment. NaCl stress also temporarily enhanced SPAPX expression starting from day 3 to day 6, and then gradually decreased until day 9 after treatment. During leaf senescence, the H2O2 amount, malondialdehyde (MDA) and ion leakage levels were also significantly increased and exhibited a negative correlation with the SPAPX expression patterns. Furthermore, exogenous purified SPAPX fusion protein significantly mitigated ethephon-mediated leaf senescence. These data conclude for the first time that an ethephon and NaCl stress-inducible ascorbate peroxidase (SPAPX) has been cloned and exhibits a negative association with ethephon and NaCl stress induced.leaf senescence and H2O2 elevation. A speculated role of SPAPX in the protection against ROS and leaf senescence caused by ethephon or NaCl stress in sweet potato leaf is suggested.