title: Interactive effects of herbicide and enhanced UV-B on growth, oxidative damage and the ascorbate-glutathione cycle in two Azolla species.
abstract: A field experiment was conducted to investigate the impact of alone and combined exposures of herbicide pretilachlor (5, 10 and 20μgml(-1)) and enhanced UV-B radiation (UV-B1; ambient +2.2kJm(-2) day(-1) and UV-B2; ambient +4.4kJm(-2) day(-1)) on growth, oxidative stress and the ascorbate-glutathione (AsA-GSH) cycle in two agronomically important Azolla spp. viz., Azolla microphylla and Azolla pinnata. Decreased relative growth rate (RGR) in both the species under tested stress could be linked to enhanced oxidative stress, thus higher H2O2 accumulation was observed, that in turn might have caused severe damage to lipids and proteins, thereby decreasing membrane stability. The effects were exacerbated when spp. were exposed to combined treatments of enhanced UV-B and pretilachlor. Detoxification of H2O2 is regulated by enzymes/metabolites of AsA-GSH cycle such as ascorbate peroxidase (APX) and glutathione reductase (GR) activity that were found to be stimulated. While, dehydroascorabte reductase (DHAR) activity, and the amount of metabolites: ascorbate (AsA), glutathione (GSH) and ratios of reduced/oxidized AsA (AsA/DHA) and GSH (GSH/GSSG), showed significant reduction with increasing doses of both the stressors, either applied alone or in combination. Glutathione-S-transferase (GST), an enzyme involved in scavenging of xenobiotics, was found to be stimulated under the tested stress. This study suggests that decline in DHAR activity and in AsA/DHA ratio might have led to enhanced H2O2 accumulation, thus decreased RGR was noticed under tested stress in both the species and the effect was more pronounced in A. pinnata. Owing to better performance of AsA-GSH cycle in A. microphylla, this study substantiates the view that A. microphylla is more tolerant than A. pinnata.
authors: Ranjan Plant Physiology and Biochemistry Laboratory, Department of Botany, University of Allahabad, Allahabad 211002 India. Electronic address: profsmprasad@gmail.com.
authors: Sheo Mohan
authors: SM
authors: Prasad
authors: Ranjan Plant Physiology and Biochemistry Laboratory, Department of Botany, University of Allahabad, Allahabad 211002 India.
authors: Sushil
authors: S
authors: Kumar
authors: Ranjan Plant Physiology and Biochemistry Laboratory, Department of Botany, University of Allahabad, Allahabad 211002 India.
authors: Parul
authors: P
authors: Parihar
authors: Ranjan Plant Physiology and Biochemistry Laboratory, Department of Botany, University of Allahabad, Allahabad 211002 India.
authors: Rachana
authors: R
authors: Singh
mesh_terms: D060387:Ascorbate Peroxidases / Q000378:metabolism; D001205:Ascorbic Acid / Q000378:metabolism*; D050260:Carbohydrate Metabolism; D004785:Environmental Pollutants / Q000633:toxicity; D029624:Ferns / Q000187:drug effects*; D005978:Glutathione / Q000378:metabolism*; D006540:Herbicides / Q000633:toxicity*; D006861:Hydrogen Peroxide / Q000378:metabolism; D010084:Oxidation-Reduction; D018384:Oxidative Stress / Q000187:drug effects*; D014466:Ultraviolet Rays / Q000009:adverse effects*
chemical_list: D004785:Environmental Pollutants; D006540:Herbicides; D006861:Hydrogen Peroxide; D060387:Ascorbate Peroxidases; D005978:Glutathione; D001205:Ascorbic Acid
keywords: Ascorbate-glutathione cycle; Enhanced UV-B; Growth rate; Oxidative stress; Pretilachlor