Exogenous proline and glycinebetaine mitigate cadmium stress in two genetically different spring wheat (Triticum aestivum L.) cultivars Rizwan Rasheed • Muhammad Arslan Ashraf • Iqbal Hussain • Muhammad Zulqurnain Haider • Uzma Kanwal • Muhammad Iqbal Received: 30 March 2014 / Revised: 7 July 2014 / Accepted: 16 July 2014 / Published online: 24 September 2014 Ó Botanical Society of Sao Paulo 2014 Abstract A pot experiment (completely randomized design with four replications) was conducted to appraise the role of exogenously applied proline and glycinebetaine in ameliorating the inhibitory effects of cadmium (Cd) in two wheat cultivars, namely Millat-2011 and Punjab-2011. The Cd stress caused a marked decrease in shoot fresh and dry masses, leaf chlorophylls, carotenoids, anthocyanins, and phenolic contents while increase in tissue malondial- dehyde (MDA) and hydrogen peroxide (H 2 O 2 ) contents. Foliar spray of proline and glycinebetaine caused a sig- nificant change in growth and physiochemical attributes of two wheat cultivars under Cd stress. Although both proline and glycinebetaine were effective, plants treated with proline had markedly greater shoot and root fresh masses, leaf phenolics, lesser degradation of chlorophylls, and accumulation of MDA and H 2 O 2 contents under Cd stress. Of the two wheat cultivars, Millat-2011 exhibited better tolerance to Cd toxicity in terms of greater leaf phenolics, lesser damage to photosynthetic pigments, and reduced accumulation of MDA and H 2 O 2 contents. Keywords Antioxidant defense system Á Cadmium Á Heavy metals Á Organic compounds Introduction Cadmium, being a non-essential metal, is among the major environmental pollutants which are considered toxic for both animals and plants (Islam et al. 2009; Hussain et al. 2013). It inhibits plant growth and development by inducing cell death due to its interference with important biochemical and physiological processes (Guo et al. 2009; Popova et al. 2009; Xu et al. 2009). Cadmium negatively affects the functions of various cellular processes through disrupted electron transport chain, loss of membrane integrity, activation/inhibition of different enzymes, and alteration in DNA (Domı ´nguez et al. 2010; Choppala et al. 2014). The exact mechanism of Cd toxicity in plants has not been fully elucidated (Domı ´nguez et al. 2010). How- ever, Cd induces oxidative stress through enhanced gen- eration of reactive oxygen species (ROS) and inhibits uptake and distribution of water and nutrients (Popova et al. 2009; Choppala et al. 2014). The superoxide radicals and H 2 O 2 are among the lethal ROS, which are formed due to the reaction of molecular oxygen with electrons leaked from electron transport chains of mitochondria and chloroplast during normal metabolic reactions (Tripathi and Gaur 2004). The ROS are highly reactive in nature and induce substantial damage to a number of macromolecules such as DNA, RNA, pig- ments, proteins, lipids, etc. (Ashraf 2009; Domı ´nguez et al. 2010; Sana et al. 2014). Redox-active metals like Fe and Cu are known to catalyze the generation of hydroxyl rad- icals by interfering in Haber–Weiss reactions, while metals without redox potential (Zn, Hg, Pb, Cd) cause increase in cellular levels of ROS by disturbing metabolic balance (Briat 2002; Tripathi and Gaur 2004). However, plants have well-developed antioxidant system comprising enzy- matic and non-enzymatic components. Enzymatic part of this antioxidant system includes superoxide dismutase (SOD), peroxidase (POD) catalase (CAT), ascorbate per- oxidase (APX), glutathione reducase (GR), while ascorbic acid, tocopherols, proline, phenolics, flavonoids, and R. Rasheed Á M. A. Ashraf (&) Á I. Hussain Á M. Z. Haider Á U. Kanwal Á M. Iqbal Department of Botany, Faculty of Science and Technology, GC University, Faisalabad, Pakistan e-mail: arsilpk@gmail.com 123 Braz. J. Bot (2014) 37(4):399–406 DOI 10.1007/s40415-014-0089-7