title: 2,4-dichlorophenoxyacetic acid-induced leaf senescence in mung bean (Vigna radiata L. Wilczek) and senescence inhibition by co-treatment with silver nanoparticles.
abstract: Leaf senescence induced by 2,4-dichlorophenoxyacetic acid (2,4-D) and senescence inhibition caused by supplementation with silver (Ag(+)) ions in the form of silver nitrate (AgNO(3)) or silver nanoparticles (AgNPs) were investigated in 8-day-old mung bean (Vigna radiata L. Wilczek) seedlings. Inhibition of root and shoot elongation were observed in mung bean seedlings treated with 500μM 2,4-D. Concomitantly, the activity of 1-aminocyclopropane-1-carboxylic acid synthase was significantly induced in leaf tissue. Leaf senescence induced by 2,4-D was closely associated with lipid peroxidation as well as increased levels of cytotoxic hydrogen peroxide (H(2)O(2)) and superoxide radicals (O(2)(·-)). Despite decreased catalase activity, the activities of peroxidase, superoxide dismutase, monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase were increased during 2,4-D-induced leaf senescence. Further, the levels of reduced ascorbate, oxidized ascorbate, and reduced glutathione were markedly decreased, whereas the level of oxidized glutathione increased. 2,4-D-induced leaf senescence in mung bean was accompanied by an increase in positive terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling, nuclear DNA fragmentation, and the activity of a 15-kDa Ca(2+)-dependent DNase. Supplementation with 100μM AgNO(3) or AgNPs inhibited 2,4-D-induced leaf senescence. The present results suggest that increased oxidative stress (O(2)(·-) and H(2)O(2)) led to senescence in mung bean leaves. Furthermore, significantly induced antioxidative enzymes are not sufficient to protect mung bean cells from 2,4-D-induced harmful ROS.
authors.affiliation: Department of Plant Sciences, Centre for Excellence in Genomic Sciences, School of Biological Sciences, Madurai Kamaraj University, Madurai 625021, India.
authors.forename: Thirupathi
authors.initials: T
authors.lastname: Karuppanapandian
authors.forename: Hong Wei
authors.initials: HW
authors.lastname: Wang
authors.forename: Natarajan
authors.initials: N
authors.lastname: Prabakaran
authors.forename: Kandhavelu
authors.initials: K
authors.lastname: Jeyalakshmi
authors.forename: Mi
authors.initials: M
authors.lastname: Kwon
authors.forename: Kumariah
authors.initials: K
authors.lastname: Manoharan
authors.forename: Wook
authors.initials: W
authors.lastname: Kim
mesh_terms: D015084:2,4-Dichlorophenoxyacetic Acid / Q000494:pharmacology*; D000975:Antioxidants / Q000378:metabolism; D002374:Catalase / Q000378:metabolism; D016922:Cellular Senescence / Q000187:drug effects; D007887:Fabaceae / Q000187:drug effects* / Q000201:enzymology; D005978:Glutathione / Q000378:metabolism; D020287:In Situ Nick-End Labeling; D015227:Lipid Peroxidation / Q000187:drug effects; D053768:Metal Nanoparticles / Q000737:chemistry*; D018384:Oxidative Stress / Q000187:drug effects; D018515:Plant Leaves / Q000187:drug effects* / Q000201:enzymology; D017382:Reactive Oxygen Species / Q000378:metabolism; D012834:Silver / Q000494:pharmacology*; D013482:Superoxide Dismutase / Q000378:metabolism
chemical_list: D000975:Antioxidants; D017382:Reactive Oxygen Species; D015084:2,4-Dichlorophenoxyacetic Acid; D012834:Silver; D002374:Catalase; D013482:Superoxide Dismutase; D005978:Glutathione