Contents lists available at ScienceDirect Ecotoxicology and Environmental Safety journal homepage: www.elsevier.com/locate/ecoenv Diminution of arsenic accumulation in rice seedlings co-cultured with Anabaena sp.: Modulation in the expression of lower silicon transporters, two nitrogen dependent genes and lowering of antioxidants activity Ruma Ranjan a,b , Navin Kumar a , Arvind Kumar Dubey a , Ambedkar Gautam a , Shyam Narain Pandey b , Shekhar Mallick a, ⁎ a CSIR-National Botanical Research Institute, Lucknow, India b University of Lucknow, Lucknow, India ARTICLE INFO Keywords: Arsenic Anabaena sp. Lower silicon transporter S-adenosylmethionine-dependent methyltransferases Oryza sativa L. ABSTRACT The present study was intended to investigate the role of algae, Anabaena sp. in the amelioration of As toxicity, when co-cultured with rice seedlings. The reduction of growth in rice seedlings against As(III) and As(V) was recovered with Anabaena sp. The Anabaena sp. also reduced the accumulation of As, where it was more efficient against 60 μM As(III) (49%) than As(V) (23%) in rice shoot. Similarly, with reduction of As accumulation, lower silicon transporters (Lsi-1 and Lsi-2) was found to be suppressed against As treatments. However, the expression of two nitrogen dependent genes i.e., NR and SAMT were found to be enhanced with the Anabaena sp. Likewise, the activity of antioxidant enzyme, GST, was enhanced, whereas, the activity of other enzymes such as SOD, APX, GPX, GR and DHAR were decreased with As+Algae combinations. Overall, the result suggested that the Anabaena sp. reduces As accumulation, modulates gene expressions and antioxidants to ameliorate the As toxicity in Oryza sativa L. 1. Introduction Arsenic (As) is a non threshold class-I carcinogen which causes many health related ailments including cancer, particularly in South- East Asian countries. The total concentration of As has been found up to 100 μM in the As contaminated regions (Tripathi et al., 2012). The problem is acute due to consumption of rice grown on As contaminated regions (Smedley and Kinniburgh, 2002). The cultivation of rice is water intensive process and is irrigated through As containing ground water in these regions. Among the cereal crops, rice is the efficient accumulator of As, as a result, it accumulates several orders of As higher in the grain than other cereal crops (Su et al., 2010). In the environ- ment, As is abundantly present in two inorganic forms i.e., arsenite [As (III)] predominantly under anaerobic and arsenate [As(V)]under aerobic conditions (Dubey et al., 2016). In rice plants, two silicon transporters are reportedly present, which facilitate the transportation of inorganic As (iAs) from soil to plants (Kumar et al., 2017). The lower silicon transporters (Lsi-1 and Lsi-2) are responsible for the As(III) mobility in the plants. WhereLsi-1 is an influx transporter primarily responsible for the transport of silicon and As(III) from the external solution to the root cells whereas, Lsi-2 has been found to mediate As (III) efflux from root to xylem across the apoplast (Ma et al., 2008). Therefore, the pathway of iAs transport from the external medium to the stele involves the influx of iAs mediated by Lsi-1 (Ma et al., 2008), and the efflux of iAs towards the stele through Lsi-2 (Zhao et al., 2008). Contrarily, the As(V) uptake takes place through the specific phosphate transporters (PHT) (Wu et al., 2011). The accumulation of As inhibits physiological and biochemical processes of the plants, through gen- eration of reactive oxygen species (ROS) (Hartley‐Whitaker et al., 2001). Oxidative stress is a complex chemical and physiological phenom- enon that appears with the biotic and abiotic stresses and generates ROS, causing structural misbalance of the biomolecules (nucleic acids, proteins and lipids). To scavenge the generated ROS, plants elevates the level of antioxidants and activities of antioxidant enzymes, to avoid stress oxidative. The antioxidant enzyme superoxide dismutase (SOD) converts superoxide (O 2 - ) into hydrogen peroxide (H 2 O 2 ) and catalase (CAT), ascorbate peroxidase (APX), glutathione peroxidase (GPX) and peroxidase (POD), coverts H 2 O 2 into H 2 O and O 2 (Gill and Tuteja, 2010). On the other hand, the microorganism plays a crucial role in de- toxification of As by methylation and bioaccumulation process https://doi.org/10.1016/j.ecoenv.2017.12.056 Received 12 September 2017; Received in revised form 26 November 2017; Accepted 27 December 2017 ⁎ Corresponding author. E-mail address: shekharm@nbri.res.in (S. Mallick). Ecotoxicology and Environmental Safety 151 (2018) 109–117 0147-6513/ © 2018 Elsevier Inc. All rights reserved. T