title: Evaluating the combined effects of pretilachlor and UV-B on two Azolla species.
abstract: The present study assessed the comparative responses of two agronomic species of Azolla (A.microphylla and A. pinnata) exposed to man-made and natural stressors by evaluating biomass accumulation, pigments (chlorophyll a and b and carotenoid contents), photosynthetic activity and nitrogen metabolism. The study was carried out in field where two species of Azolla were cultured and treated with various concentrations (5, 10 and 20 μg ml(-1)) of herbicide; pretilachlor [2-chloro-2,6-diethyl-N-(2-propoxyethyl) acetanilide] and enhanced levels (UV-B1: ambient +2.2 kJ m(-2) day(-1) and UV-B2: ambient +4.4 kJ m(-2) day(-1)) of UV-B, alone as well as in combination. Biomass accumulation, photosynthetic pigments; chlorophyll a, b and carotenoids, photosynthetic oxygen yield and photosynthetic electron transport activities i.e. photosystem II (PS II) and photosystem I (PS I) in both the species declined with the increasing doses of pretilachlor and UV-B radiation, which further declined when applied in combination. The lower doses (5 and 10 μg ml(-1)) of pretilachlor and UV-B (UV-B1 and UV-B2) alone, damaged mainly the oxidation side of PS II, whereas higher dose (20 μg ml(-1)) of pretilachlor alone and in combination with UV-B1 and UV-B2 caused damage to PS II reaction centre and beyond this towards the reduction side. A significant enhancement in respiration was also noticed in fronds of both the Azolla species following pretilachlor and UV-B treatment, hence indicating strong damaging effect. The nitrate assimilating enzymes - nitrate reductase and nitrite reductase and ammonium assimilating enzymes - glutamine synthetase and glutamate synthase were also severely affected when treated either with pretilachlor and/or UV-B while glutamate dehydrogenase exhibited a stimulatory response. The study suggests that both the species of Azolla showed considerable damage under pretilachlor and UV-B treatments alone, however, in combination the effect was more intense. Further, in comparison to A. pinnata, A. microphylla exhibited greater resistance against tested doses of both the stresses, either alone or in combination.
authors.affiliation: Ranjan Plant Physiology and Biochemistry Laboratory, Department of Botany, University of Allahabad, Allahabad 211002, India. Electronic address: profsmprasad@gmail.com.
authors.forename: Sheo Mohan
authors.initials: SM
authors.lastname: Prasad
authors.affiliation: Ranjan Plant Physiology and Biochemistry Laboratory, Department of Botany, University of Allahabad, Allahabad 211002, India.
authors.forename: Sushil
authors.initials: S
authors.lastname: Kumar
authors.affiliation: Ranjan Plant Physiology and Biochemistry Laboratory, Department of Botany, University of Allahabad, Allahabad 211002, India.
authors.forename: Parul
authors.initials: P
authors.lastname: Parihar
authors.affiliation: Ranjan Plant Physiology and Biochemistry Laboratory, Department of Botany, University of Allahabad, Allahabad 211002, India.
authors.forename: Anita
authors.initials: A
authors.lastname: Singh
authors.affiliation: Ranjan Plant Physiology and Biochemistry Laboratory, Department of Botany, University of Allahabad, Allahabad 211002, India.
authors.forename: Rachana
authors.initials: R
authors.lastname: Singh
mesh_terms: D000083:Acetanilides / Q000494:pharmacology*; D018533:Biomass; D010788:Photosynthesis; D010860:Pigments, Biological / Q000378:metabolism; D057949:Streptophyta / Q000187:drug effects* / Q000528:radiation effects*; D014466:Ultraviolet Rays
chemical_list: D000083:Acetanilides; D010860:Pigments, Biological; C118050:pretilachlor
keywords: Biomass accumulation; Enhanced UV-B; Nitrogen metabolism; Photosynthetic pigment; Pretilachlor; Respiration