title: Delayed senescence of apple leaves by exogenous melatonin treatment: toward regulating the ascorbate-glutathione cycle.
abstract: The objectives of this study were to test the effects of exogenous melatonin on apple (Malus domestica Borkh. cv. Golden Delicious) leaves and investigate its possible physiological role in delaying leaf senescence. Detached leaves treated with 10 mm melatonin solutions clearly showed a slowing in their process of dark-induced senescence, as evidenced by both biochemical and molecular parameters. Melatonin delayed the normal reduction in chlorophyll content and maximum potential photosystem II efficiency (F(v) /F(m) ). It also suppressed the transcript levels of a key chlorophyll degradation gene, pheide a oxygenase (PAO), and the senescence-associated gene 12 (SAG12). This outcome was thought to be because of the enhanced antioxidant capabilities of melatonin. Indeed, H(2) O(2)  accumulation was inhibited by exogenous melatonin, which might have resulted from direct reactive oxygen species scavenging by melatonin and a great enhancement of ascorbate peroxidase (APX; EC 1.11.1.11), which acted on both mRNA and protein activity levels. Melatonin treatment led to the maintenance of higher contents of ascorbic acid (AsA) and glutathione (GSH) but less dehydroascorbate (DHA) and oxidized glutathione (GSSG) compared with the control, possibly through its regulation of the AsA-GSH cycle.
authors: State Key Laboratory of Crop Stress Biology in Arid Areas/College of Horticulture, Northwest A&F University, Yangling, Shaanxi, China.
authors: Ping
authors: P
authors: Wang
authors: Lihua
authors: L
authors: Yin
authors: Dong
authors: D
authors: Liang
authors: Chao
authors: C
authors: Li
authors: Fengwang
authors: F
authors: Ma
authors: Zhiyong
authors: Z
authors: Yue
mesh_terms: D000975:Antioxidants / Q000494:pharmacology*; D060387:Ascorbate Peroxidases / Q000378:metabolism; D001205:Ascorbic Acid / Q000378:metabolism; D016922:Cellular Senescence / Q000187:drug effects*; D002734:Chlorophyll / Q000378:metabolism; D003546:Cysteine Endopeptidases / Q000378:metabolism; D005978:Glutathione / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000494:pharmacology; D027845:Malus / Q000166:cytology / Q000378:metabolism*; D008550:Melatonin / Q000494:pharmacology*; D016877:Oxidants / Q000494:pharmacology; D010084:Oxidation-Reduction / Q000187:drug effects; D010105:Oxygenases / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000378:metabolism; D018515:Plant Leaves / Q000166:cytology / Q000378:metabolism*; D010940:Plant Proteins / Q000378:metabolism
chemical_list: D000975:Antioxidants; D016877:Oxidants; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D002734:Chlorophyll; D006861:Hydrogen Peroxide; D060387:Ascorbate Peroxidases; D010105:Oxygenases; C112915:pheide a oxygenase; D003546:Cysteine Endopeptidases; D005978:Glutathione; D008550:Melatonin; D001205:Ascorbic Acid