Cadmium stress in rice plants: The effect of cadmium on seed germination and seedling growth of rice plant (Oryza sativa L.)

Abstract

Cadmium (Cd) non-essential, but toxic, element for animals and plants is frequently present in paddy fields. Oryza sativa L., a staple food for at least the half of world population, also aquatic plants are known to accumulate heavy metals, easily absorbs Cd by the root, and in this organ, the pollutants evoke consistent damages and reducing the root system. In this study, the effects of different cadmium chloride concentrations (0,15, 25, 35, 45, and 55 ?M) on some physiological and biochemical processes including seed germination, root and shoot fresh and dry weight in rice were investigated. The results showed that after treatment, the seed germination rate was less affected, but root growth was restrained evidently. It affected the subsequent growth rate in these plants. Higher cadmium concentrations especially at 45 and 55 ?M reduced plant growth significantly. Leaf chlorosis, wilting and leaf abscission was observed in plants treated with cadmium. Also, Cd treatment reduced the germination percentage by 6.9%, root and shoots length by 68.9% and 85.6%, respectively. A decrease of 42.3% in fresh weight was noticed following the treatment with 45, and 55 ?M cadmium doses compared with the control treatment, respectively. Based on the results we concluded that these traits of the rice plants are seriously affected by Cd treatment and also these are symptoms of toxicity of the Cd element. Our results demonstrate that Cd affects the rice root system, by interfering with the formation of the roots and their development. This results in an important change in the root system architecture, which may negatively affect plant survival in highly polluted paddy soils. Therefore, less amount of reduction in a special genotype is referred to as the index of tolerance to Cd. Finally, in the metal-contaminated areas, further research is needed to determine different levels of metals in the environment and various parts of the plants. Having in mind the value of this crop as a food all over the world, the consequences of the reactivity of its root system to these pollutants is very important for evaluating possible economic losses, and for executing repair strategies.