Contents lists available at ScienceDirect Aquatic Toxicology journal homepage: www.elsevier.com/locate/aqtox Biometric and physiological responses of Egeria densa Planch. cultivated with toxic and non-toxic strains of Microcystis Cihelio A. Amorim, Cláudia Ulisses, Ariadne Nascimento Moura ⁎ Programa de Pós-Graduação em Botânica, Departamento de Biologia, Universidade Federal Rural de Pernambuco – UFRPE, Av. Manoel de Medeiros, s/n, Dois Irmãos, CEP 52171-900, Recife, PE, Brasil, Brazil ARTICLE INFO Keywords: Aquatic macrophytes Cyanotoxins Growth inhibition Microcystins Microcystis aeruginosa Oxidative stress ABSTRACT Cyanobacterial blooms are becoming increasingly common in aquatic environments around the world, mainly due to eutrophication and climate change. Cyanotoxin-producing strains (e.g., microcystins (MC) producers) may be present in these blooms, affecting the growth of other aquatic organisms, such as aquatic macrophytes. In this study, we evaluated the morphometric and physiological responses of the aquatic macrophyte Egeria densa to the exposure to a toxic strain of Microcystis aeruginosa (MCs producer) and a non-toxic Microcystis panniformis (non-MC producer). The effects of Microcystis strains on E. densa growth and biomass were verified for five weeks (Experiment 1) and physiological responses were evaluated for 14 days (Experiment 2). Prolonged exposure of E. densa to the MC producing strain reduced growth, accompanied by the inhibition of shoot and root emission. Both Microcystis strains caused a decrease in the content of photosynthetic pigments, like total chlorophyll and chlorophyll a and b, accompanied by an increase of carotenoids. At the beginning of the MC-producing strain exposure, E. densa showed an increase in the activity of the anti-oxidative enzymes superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX), accompanied by an increase in the levels of malondialdehyde, indicating lipid peroxidation. During the 14th day of exposure, the activity of antioxidant enzymes remained similar to the control, suggesting that E. densa has an efficient anti-oxidative system to control the reactive oxygen species produced in response to the stress caused by microcystins. However, when prolonged exposure occurred, possible damage to proteins may have affected the growth and development of E. densa. No changes were observed in the enzymatic activity of the plants exposed to the non-MC producing strain, suggesting that this cyanobacterial strain do not cause significant damage to the development of E. densa. These results are important for understanding the anti-oxidative defense mechanisms of aquatic macrophytes when coexisting with an MC producing strain. 1. Introduction Aquatic macrophytes are important for maintaining a clear state of shallow lakes (Scheffer et al., 1993), because they present mechanisms that reduce the amount of phytoplankton biomass, either indirectly, by providing shelter for zooplankton (Jeppesen et al., 1997), or directly, by releasing chemical compounds that inhibit phytoplankton growth (Hilt and Gross, 2008; Eigemann et al., 2013). However, eutrophication and global temperature rise, as effects of climate change, favor the persistence of harmful cyanobacterial blooms (CyanoHABs) (Mariani et al., 2015; Paerl et al., 2016; Lürling et al., 2017). These blooms may pose contamination risk to man and aquatic organisms, mainly due to the release of cyanotoxins (Paerl and Otten, 2013; Carmichael and Boyer, 2016). The synthesis of these toxins in blooming events favors cyanobacteria growth, as it inhibits the growth of competing species through allelopathy and kills the predators of cyanobacteria (Granéli et al., 2008). Submerged macrophytes are strongly affected by these cyanotoxins because they are in direct contact with these metabolites in the water (Pflugmacher, 2004). Among the bloom-forming cyanobacteria, Microcystis aeruginosa Kütz. stands out as the most commonly recorded species in continental aquatic environments around the world (Harke et al., 2016). This species is able to synthesize several variants of microcystins (MCs), which are the most harmful and widely distributed hepatotoxins (Martins and Vasconcelos, 2009; Paerl and Huisman, 2009). To date, more than 240 variants of MCs are known (Svirčev et al., 2017; Spoof and Catherine, 2017), among them MC-LR is the most frequent in aquatic ecosystems and mainly acts in the inhibition of protein phos- phatases 1 and 2A (PP1 and PP2A, respectively) (MacKintosh et al., 1990; Dawson, 1998). The toxicity of MCs has been demonstrated in http://dx.doi.org/10.1016/j.aquatox.2017.08.012 Received 14 July 2017; Received in revised form 14 August 2017; Accepted 16 August 2017 ⁎ Corresponding author. E-mail addresses: ariadne_moura@hotmail.com, ariadne.moura@ufrpe.br (A.N. Moura). Aquatic Toxicology 191 (2017) 201–208 0166-445X/ © 2017 Elsevier B.V. All rights reserved. MARK