Journal of Plant Physiology 173 (2015) 9–18 Contents lists available at ScienceDirect Journal of Plant Physiology journal h om epage: www.elsevier.com/locate/jplph Physiology Selenium and sulfur influence ethylene formation and alleviate cadmium-induced oxidative stress by improving proline and glutathione production in wheat M. Iqbal R. Khan, Faroza Nazir, Mohd. Asgher, Tasir S. Per, Nafees A. Khan ∗ Plant Physiology Section, Department of Botany, Aligarh Muslim University, Aligarh 202 002, India a r t i c l e i n f o Article history: Received 3 July 2014 Received in revised form 29 September 2014 Accepted 29 September 2014 Available online 7 October 2014 Keywords: Cadmium Ethylene Photosynthesis Selenium Sulfur s u m m a r y We have studied the influence of selenium (Se) and sulfur (S) in the protection of photosynthetic capacity of wheat (Triticum aestivum) against cadmium (Cd) stress. The involvement of ethylene and its interaction with proline and antioxidant metabolism in the tolerance of plants to Cd stress was evaluated. Application of Se or S alleviated Cd-induced oxidative stress by increasing proline accumulation as a result of increased activity of glutamyl kinase (GK) and decreased activity of proline oxidase (PROX). These nutrients also induced the activity of ATP-sulfurylase and serine acetyl transferase and the content of cysteine (Cys), a precursor for the synthesis of both reduced glutathione (GSH) and ethylene. Further, application of Se and S to plants under Cd stress reduced ethylene level and increased the activity of glutathione reductase (GR) and glutathione peroxidase (GPX), reduced oxidative stress and improved photosynthesis and growth. The involvement of ethylene in Se and S-mediated alleviation of Cd stress was substantiated with the use of ethylene biosynthesis inhibitor aminoethoxyvinylglycine (AVG). The use of AVG reversed the effects of Se and S on ethylene, content of proline and GSH and photosynthesis. The results suggested that Se and S both reversed Cd-induced oxidative stress by regulating ethylene formation, proline and GSH metabolism. Thus, Se or S-induced regulatory interaction between ethylene and proline and GSH metabolism may be used for the reversal of Cd-induced oxidative stress. © 2014 Elsevier GmbH. All rights reserved. Introduction Cadmium (Cd) is a powerful pollutant due to its long half life in soil and greater solubility in water. Plants grown under excess Cd show reduced growth and metabolism. Elevated levels of Cd induce excessive production of reactive oxygen species (ROS). These ROS cause damage to photosynthetic apparatus resulting in adverse effects on photosynthetic potential of plants (Mobin and Khan, Abbreviations: ACS, 1-aminocyclopropane carboxylic acid synthase; ATP-S, adenosine triphosphate sulfurylase; AVG, aminoethoxyvinylglycine; Cd, cadmium; Cys, cysteine; DAS, days after sowing; ETR, electron transport rate; GK, glutamyl kinase; GPX, glutathione peroxidase; GR, glutathione reductase; GSH, reduced glu- tathione; NPQ, non-photochemical quenching; NR, nitrate reductase; PROX, proline oxidase; PS, photosystem; qP, photochemical quenching; ROS, reactive oxygen species; Rubisco, ribulose-1,5-bisphosphate carboxylase/oxygenase; S, sulfur; SAT, serine acetyltransferase; Se, selenium; TBARS, thiobarbituric acid reactive sub- stances. ∗ Corresponding author. Tel.: +91 571 2702016; fax: +91 571 2702016. E-mail address: naf9@lycos.com (N.A. Khan). 2007; Astolfi et al., 2012; Dias et al., 2013; Asgher et al., 2014). Several efforts have been made to counteract Cd-induced toxicity and restore the photosynthetic ability of plants. Supplementation of plants with mineral elements is one of the strategies adopted. The added mineral elements benefit plants because of their known biological role in metabolism and also help to reduce the toxic- ity generated by Cd. It has been reported that inputs of essential or beneficial nutrients such as nitrogen (N), sulfur (S), iron (Fe) and selenium (Se) restore photosynthetic ability, improve antiox- idants capacity and productivity of crop plants (Iqbal et al., 2011; Hasanuzzaman and Fujita, 2011; Hasanuzzaman et al., 2011; Astolfi et al., 2012; Asgher et al., 2014). Sulfur is an essential mineral nutrient element and an integral part of certain amino acids (cysteine, Cys and methionine), antiox- idant (reduced glutathione; GSH), co-enzymes, prosthetic groups, vitamins, secondary metabolites, phytochelatins (PCs) and lipids (Khan et al., 2014a,b). The role of S in detoxification of Cd-induced oxidative stress was correlated with adequate S availability in Hordeum vulgare and Brassica juncea plants with increased GSH pro- duction (Astolfi et al., 2012; Masood et al., 2012; Asgher et al., 2014). http://dx.doi.org/10.1016/j.jplph.2014.09.011 0176-1617/© 2014 Elsevier GmbH. All rights reserved.