Responses of Antioxidative Defense System and Composition of Photosynthetic Pigments in Brassica juncea L. upon Imidacloprid Treatments
Responses of Antioxidative Defense System and Composition of Photosynthetic Pigments in Brassica juncea L. upon Imidacloprid Treatments
Mudasir Irfan Dar*, Fareed Ahmad Khan and Farha Rehman
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ABSTRACT
The effect of the insecticide Imidacloprid on photosynthetic pigments and antioxidative enzymes in Brassica juncea L. cv. alankar was investigated. Forty-day-old pot plants were exposed to different concentrations of the insecticide, ranging from 0 to 40 grams active ingredient per hectare (g.a.i ha-1) through foliar spray. Analyses were done at days 3, 7, and 15 after treatment. Lipid peroxidation rates and contents of proline, ascorbate (ASC), glutathione (GLU), antioxidative enzymes; superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) were assessed. Imidacloprid enhanced malondi- aldehyde (MDA) and proline contents over their respective controls at all doses and growth stages observed, attaining maximum with 40 grams Imidacloprid active ingredient per hectare-1 at day 15 after treatment. The antioxidative enzyme activity of SOD, APX and GR showed increasing trend in a dose-dependent manner, attaining maximum at 40 g.a.i ha-1 of Imidacloprid treatment at day 7 after treatment (DAT) followed by 3 and 15 DAT, respectively. On the contrary, the CAT activity was increased at lower concentrations of Imida- cloprid but showed a dose dependence decline at higher concentrations of the insecticide at all the observed growth stages, with maximum decrease under 40 g.a.i ha-1 at 15 DAT followed by 3 and 7 DAT respectively. Among the non-enzymatic antioxidants, a dose dependent decline was observed in Ascorbate (ASC), de- hydroascorbate (DHA) and reduced glutathione (GSH) levels. The photosynthetic pigments showed slight increases over their respective controls at lower concentrations of the insecticide at all the growth stages, but at higher concentrations (30 and 40 g.a.i ha-1), both the pigments were decreased considerably at all the observed growth stages. These results suggested that the lower concentrations of Imidacloprid applied on the mustard might have no severe effect on the mustard plant because of the regulation of the anti-oxidative enzyme system and MDA, but provoked oxidative stress when applied at high dosages. Therefore, pesticide application at high concentrations can be considered as a kind of stress, similarly to other stresses such as salt, drought and low or high temperatures.
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