Differential effects of glyphosate and aminomethylphosphonic acid (AMPA) on photosynthesis and chlorophyll metabolism in willow plants Marcelo Pedrosa Gomes a,c , Sarah Gingras Le Manac'h a , Sophie Maccario c , Michel Labrecque b , Marc Lucotte c , Philippe Juneau a, ⁎ a Université du Québec à Montréal, Department of Biological Sciences, TOXEN, Ecotoxicology of Aquatic Microorganisms Laboratory, Succ. Centre-Ville, Montréal H3C 3P8, Québec, Canada b Institut de Recherche en Biologie Végétale, Montreal Botanical Garden, 4101 Sherbrooke East, Montréal H1X 2B2, Québec, Canada c Université du Québec à Montréal, Institut des Sciences de l'environnement & GEOTOP, Succ. Centre-Ville, C.P. 8888, Montréal H3C 3P8, Québec, Canada abstract article info Article history: Received 25 March 2015 Received in revised form 26 November 2015 Accepted 27 November 2015 Available online xxxx We used a willow species (Salix miyabeana cultivar SX64) to examine the differential secondary-effects of glyph- osate and aminomethylphosphonic acid (AMPA), the principal glyphosate by-product, on chlorophyll metabolism and photosynthesis. Willow plants were treated with different concentrations of glyphosate (equivalent to 0, 1.4, 2.1 and 2.8 kg ha -1 ) and AMPA (equivalent to 0, 0.28, 1.4 and 2.8 kg ha -1 ) and evaluations of pigment contents, chlorophyll fluorescence, and oxidative stress markers (hydrogen peroxide content and antioxidant enzyme activ- ities) in leaves were performed after 12 h of exposure. We observed that AMPA and glyphosate trigger different mechanisms leading to decreases in chlorophyll content and photosynthesis rates in willow plants. Both chemicals induced ROS accumulation in willow leaves although only glyphosate-induced oxidative damage through lipid peroxidation. By disturbing chlorophyll biosynthesis, AMPA induced decreases in chlorophyll contents, with con- sequent effects on photosynthesis. With glyphosate, ROS increases were higher than the ROS-sensitive threshold, provoking chlorophyll degradation (as seen by pheophytin accumulation) and invariable decreases in photosyn- thesis. Peroxide accumulation in both AMPA and glyphosate-treated plants was due to the inhibition of antioxidant enzyme activities. The different effects of glyphosate on chlorophyll contents and photosynthesis as described in the literature may be due to various glyphosate:AMPA ratios in those plants. © 2015 Published by Elsevier Inc. Keywords: Aminolevulinic acid Herbicide Oxidative stress Pigments ROS Photosynthesis 1. Introduction Since the introduction of glyphosate-resistant (GR) plants, glyphosate-based products have become the most widely used herbicides globally. Glyphosate has a short half-life and has been considered one of the least toxic herbicides [1,2]. However, following glyphosate application and its degradation by microorganisms, the aminomethylphosphonic acid (AMPA), the principal glyphosate by-product, was detected in soils and in water [1]. Similarly to soil and aquatic microorganisms, it was pro- posed that some plants can metabolize glyphosate to sarcosine through C-P lyase activity [3], or to AMPA through glyphosate oxidase (GOX) ac- tivity [4]. GOX pathway is usually the most expected one, since AMPA is found as the major glyphosate-metabolite in plants [5]. In addition to AMPA produced through glyphosate metabolism, plants can also be pre- sumably exposed to AMPA through their contact with environmental ma- trices (i.e., soil and water) [1]. However, not so many studies have examined the effects of AMPA on plants [4,6,7] and to date, only high AMPA concentrations were described to induce detrimental effects in GR and non-GR plants [6]. Glyphosate effects on plant physiological processes have recently been reviewed [8], and include deleterious effect on photosystem II quan- tum efficiency as well as electron transport rate (ETR). It is known that de- creased photochemical efficiency is associated with glyphosate-induced decreases in chlorophyll contents [9–11], although the exact mechanisms by which glyphosate affects chlorophyll contents are not well known. It was assumed that by disturbing plant mineral nutrient (i.e., Mg and Fe) uptake, glyphosate can affect chlorophyll biosynthesis [12]. However, glyphosate effects on mineral nutrition is contradictory, and a number of studies did not report any effect [13,14]. It was proposed that even at high glyphosate concentrations in the plant phloem, glyphosate was un- able to compete with biological chelating agents for minerals implicated in chlorophyll biosynthesis [15]. Reddy et al. [4], alternatively argued that AMPA, and not glyphosate, was responsible for the deleterious effects observed on chlorophyll biosynthesis in GR soybeans. It is important to note, however, that decreased chlorophyll contents have been observed even in plants that do not degrade glyphosate to AMPA [9,10]. Increased reactive oxygen species (ROS) concentrations and oxidative stress have been also observed in glyphosate-exposed plants [16,17], as in many other herbicide-exposed plants [18], although according to Moldes et al. [19] the slight oxidative stress induced by glyphosate has no relevance to plant mortality. However, it is widely accepted that modulation in Pesticide Biochemistry and Physiology xxx (2015) xxx–xxx ⁎ Corresponding author. E-mail address: juneau.philippe@uqam.ca (P. Juneau). YPEST-03902; No of Pages 6 http://dx.doi.org/10.1016/j.pestbp.2015.11.010 0048-3575/© 2015 Published by Elsevier Inc. Contents lists available at ScienceDirect Pesticide Biochemistry and Physiology journal homepage: www.elsevier.com/locate/pest Please cite this article as: M.P. Gomes, et al., Differential effects of glyphosate and aminomethylphosphonic acid (AMPA) on photosynthesis and chlorophyll metabolism in willow pl..., Pesticide Biochemistry and Physiology (2015), http://dx.doi.org/10.1016/j.pestbp.2015.11.010