Exogenous calcium alleviates cadmium-induced oxidative stress in rice (Oryza sativa L.) seedlings by regulating the antioxidant defense and glyoxalase systems Calcium-induced cadmium stress tolerance in rice Anisur Rahman 1,2 • Mohammad Golam Mostofa 1 • Kamrun Nahar 1,3 • Mirza Hasanuzzaman 2 • Masayuki Fujita 1 Received: 10 August 2015 / Accepted: 30 November 2015 Ó Botanical Society of Sao Paulo 2015 Abstract The present study was undertaken to investigate the regulatory role of exogenous application of calcium (Ca) in enhancing the antioxidant defense and glyoxalase systems in mitigating cadmium (Cd) stress in rice. Hydroponically grown 14-day-old rice (Oryza sativa L. cv. BRRI dhan29) seedlings were exposed to 0.25 and 0.5 mM CdCl 2 alone and in combination with 2.5 mM CaCl 2 for 3 days. Exposure to Cd caused chlorosis, leaf rolling symptoms, and growth inhibition. A higher concentration of Cd in the growth med- ium resulted in higher Cd accumulation, which induced oxidative stress through overproduction of reactive oxygen species (ROS) by disrupting the antioxidant defense system. Cadmium treatment increased the methylglyoxal (MG) level. Calcium supplementation in the Cd-treated growth medium reduced Cd uptake. Application of Ca also significantly increased the (ascorbate) AsA content, increased the activities of superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase (GST), monodehydroascorbate reductase (MDHAR), and dehydroascorbate reductase (DHAR) in the antioxidant system, and increased the glyoxalase I (Gly I) and glyoxalase II (Gly II) activities in the glyoxalase system in rice seedlings exposed to both levels of Cd. Exogenous Ca appli- cation regulated the antioxidant defense and glyoxalase sys- tems, which reversed overproduced ROS and detoxified MG, which in turn reduced Cd toxicity. Keywords Abiotic stress Á Ca signaling Á Cd toxicity Á Methylglyoxal Á Oxidative stress Abbreviations AO Ascorbate oxidase APX Ascorbate peroxidase AsA Ascorbate BSA Bovine serum albumin Cd Cadmium Ca Calcium CAT Catalase CDNB 1-Chloro-2,4-dinitrobenzene Chl Chlorophyll DAB Diaminobenzidine DHA Dehydroascorbate DHAR Dehydroascorbate reductase DTNB 5,5 0 -Dithio-bis-(2-nitrobenzoic) acid EDTA Ethylenediaminetetraacetic acid Gly Glyoxalase GR Glutathione reductase GSH Reduced glutathione GSSG Oxidized glutathione GPX Glutathione peroxidase GST Glutathione S-transferase LOX Lipoxygenase MDA Malondialdehyde MDHA Monodehydroascorbate MDHAR Monodehydroascorbate reductase MG Methylglyoxal NADPH Nicotinamide adenine dinucleotide phosphate & Masayuki Fujita fujita@ag.kagawa-u.ac.jp Mirza Hasanuzzaman mhzsauag@yahoo.com 1 Laboratory of Plant Stress Responses, Department of Applied Biological Science, Faculty of Agriculture, Kagawa University, Miki-cho, Kita-gun, Kagawa 761-0795, Japan 2 Department of Agronomy, Faculty of Agriculture, Sher-e- Bangla Agricultural University, Sher-e-Bangla Nagar, Dhaka 1207, Bangladesh 3 Department of Agricultural Botany, Faculty of Agriculture, Sher-e-Bangla Agricultural University, Sher-e-Bangla Nagar, Dhaka 1207, Bangladesh 123 Braz. J. Bot DOI 10.1007/s40415-015-0240-0