International Journal of Forest, Soil and Erosion (IJFSE), 2012, 2 (3) www.ijfse.com Shabestar, Iran | 128 Int. J. Forest, Soil and Erosion, 2012 2 (3): 128-132 ISSN 2251-6387 © August 2012, GHB's Journals, IJFSE, Shabestar, Iran Research Paper Biochemical and physiological responses of rice cadmium Mohammad Reza Amirjani (Iran) Mohammad Reza Amirjani Department of Biology, Faculty of Sciences, Arak University, Arak 38156-8-8349, Iran E-mail: m-amirjani@araku.ac.ir Received: 2012-02-06 Accepted: 2012-04-09 Abstract: Cadmium (Cd) is a non-essential heavy metal that is recognized as a major environmental pollutant. Cd enters the ecosystem chiefly as the result of human activities. Present investigation was conducted to assess the biochemical and physiological responses of rice to different concentrations of Cd. Seeds of rice were sterilized and were allowed to germinate under various Cd concentrations. Cadmium caused a gradual decrease in vigor index, root length, shoot height and amylase activity. Germination indexes of treated seeds were decreased. Root length decreased under all treatments. Cadmium uptake by seedlings increased with increasing Cd concentration and followed Michaelis-Menten kinetics. The average total amylolytic activities of rice seeds did not have a significant change in less than 4mg Cd l-1 medium compared to the control, but activity was progressively depressed with increasing concentration of Cd (6–10 mg l-1). Antioxidative responses of rice seedlings were also explored. Antioxidant enzyme activity in rice leaves generally showed no significant changes at low levels of Cd exposure. But high levels of Cd stimulated enzyme activity. These results suggested that prompt antioxidative responses might be necessary for the reduction of Cd-induced oxidative stress in roots but not in leaves. Keywords: cadmium, rice, Oryza sativa, antioxidative response This article should be referenced as follows: Amirjani M R (2012). Biochemical and physiological responses of rice cadmium, International Journal of Forest, Soil and Erosion, 2 (3): 128-132. Introduction Environmental pollution caused by the release of a wide range of compounds as a consequence of industrialization has now assumed serious proportions (Jain et al., 2005). Industrial effluents are responsible for serious water (Otokunefor and Obiukwu, 2005) and soil pollution (Konwar and Jha, 2010), which is considered as one of the major factors responsible for low productivity of crops. A considerable number of reports are available on the effect of different industrial effluents on different crops (Cabral et al., 2010; Naaz and Pandey, 2010). Cadmium (Cd) is one of the most serious pollutants, and massive amounts are released into the environment by human activities (Nriagu and Pacyna, 1988) whereas In areas little affected by human activities, Cd is only released during the weathering of rocks. Cd is a heavy metal that enters the environment mainly from industrial processes and phosphate fertilizers and is transferred to animals and humans through the food chain. In the natural environment, the cadmium content in igneous rocks is generally low and has no clear relationship with the concentration of other chemical elements other than Zn. Cd does not have any known biological functions and is highly toxic, for humans, animals, and plants, and is one of the widespread pollutants with a long biological half-life (Chirila et al., 2009). Cadmium has recently been shown to be an endocrine-disrupting chemical with estrogenic properties and a potential prostate carcinogen (Benbrahim-Tallaa et al., 2007). Cd toxicity effects in plants include inhibition of physiological processes such as respiration, photosynthesis, interference with electron-transport chains, plant– water relationship, nitrogen and mineral nutrition. Thus Cd toxicity leading to reduced plant growth, even to death (Pál et al., 2006). Cd is a nonredox metal unable to participate in Fenton and/or Haber–Weiss reactions, but it causes oxidative stress by generating reactive oxygen species (ROS) . Rice (Oryza sativa L.) is an important crop worldwide and is the staple food in the diet of more than one third of the world’s population (Jung et al., 2005; Konwar and Jha, 2010). Rice is also considered to be a model plant among monocots for biological research because of its small genome size (Goff et al., 2002; Yu et al., 2002). The growth and yield of rice depends upon various factors, one of which is the soil quality. Soil pollution is a major cause of change in the quality of the soil. The increased level of ROS induced by Cd is connected with its toxicity, and Cd-related phenomena also include effects on nucleic acids, proteins and gene expression (Deckert, 2005). Cd has a high affinity for protein–thiol groups, thereby inhibiting some essential enzymes (Baudouin-Cornu and Labarre, 2006).. Recently, several literatures focused on specific organs such as barley vacuoles (Schneider et al., 2009), Indian mustard roots (Alvarez et al., 2009) to describe the Cd effects in stressed plants. Detailed proteome analyses of rice have also been done for deeper insights into complex cellular processes (Agrawal et al., 2009; Ahsan et al., 2009; Aina et al., 2007). Cd causes to inhibition of photosynthesis, such as biosynthesis of chlorophyll and functioning of photochemical reactions . Photosystem II (PSII) is extremely sensitive to Cd and its function was inhibited to a much greater extent than that of Photosystem I (PSI). Recent studies have also indicated that Cd exerts multiple effects on both donor and acceptor sites of PSII. On the donor site, the presence of Cd inhibits the oxygen evolving cycle and, consequently, oxygen evolution; on the acceptor site, it inhibits electron transfer from Q A  to Q B  (Sigfridsson et al., 2004). The aim of the present study was to investigate the effect of Cd stress on germination and seedling growth of rice. The germination parameters, Cd concentration, and activities of total amylase, -amylase, and -amylase in seeds were determined. Methods Plant material, growth conditions and growth and germination assay Rice (Oryza sativa L. cv. Tarom Atri) seeds were surface-sterilized and soaked in distilled waterfor 24 h and then sited on filter papers placed in Petri dishes moistened with distilled water containing various Cd concentrations (0, 2, 4, 6, 8, and 10 mM), supplied as CdCl 2 . After germination seedlings were grown on pots filled with vermiculite saturated with Hoagland nutrient solution (Hoagland and Arnon, 1950) supplemented with 0, 2, 4, 6, 8 and 10 mM CdCl 2 . root and shoot lengths of 12-d-old seedlings were measured. Germination percentage, germination index, and vigor index were calculated according to (Liu et al., 2005; Mhatre and Chaphekar, 1982). Seedling biomass was also determined.