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MATERIALS AND METHODS
Virus identification and propagation: Sample from naturally infected onion plants exhibiting characteristic IYSV were collected from the Experimental farm of Faculty of Agriculture , Cairo University. The observed symptoms included chlorotic or necrotic ,straw –colored to white, dry, elongate or spindle shaped lesions. Indirect ELISA technique described by Converse and Martin (1990) was conducted to test the collected samples using an induced antiserum for IYSV ( El-Shazly et al., 2006). The positive samples reacting with IYSV antiserum were used as a source of virus and mechanically inoculated to indicator host plants . The samples were inoculated to Chenopodium quinoa, Chenopodium murale , Datura stramonium, …show more content…
The homogenate was centrifuged at 12000 g for 15 min at 4 ºC. The resulting supernatant was used for analyses of enzyme activities, GSH, lipid peroxidation and protein …show more content…
Enzymes assay: The activity of cytosolic superoxide dismutase( SOD) was assayed by measuring its ability to inhibit the photochemical reduction of NBT according to method of ( Ginnopolitis and Ries 1977). Spectrophotometrically method as described by Amako et al., ( 1994) was used to assay the peroxidase (POD) activity, polyphenol oxidase ( PPO) activity was assayed by using photochemical method as described by Coseteng & Lee (1987) and phenylalanine ammonia- lyase (PAL) activity was done according to Dickerson et al., ( 1984). Determination of lipid peroxidation products: The lipid peroxidation products was estimated by the formation of thiobarbaturic acid reactive substances (TBARS) and quantified in term of malonaldheyde (MDA) as described by Haraguchi et al., ( 1997). The lipid peroxidation was expressed as micromoles of MDA .The extinction coefficient of TBARS was taken as 1.56 ×10 5 mM at wave length 532 nm. Determination of glutathione (GSH): The GSH content was estimated by the acid –soluble sulfhydryl (SH) level in the tissue homogenates as described by Vecchia et al.,(