Effect of cadmium stress on morphological and physiological traits of milk thistle (Silybum marianum)

Cadmium (Cd) is a heavy metal that causes oxidative stress in plants. In this study toxicity effect of Cd on Silybum marianum was investigated. Four treatments of CdCl2 (0, 300, 600, 400 and 900 μM) were evaluated in five replications using complete random design. Results of tolerance stress index severity of Cd stress on plants under various levels of treatments. Shoot dry weight, leaf area, chlorophyll a content, and total chlorophyll content were significantly reduced in 900 μM of Cd. Chlorophyll b decreased in all levels of Cd stress in comparison with control. Meanwhile, Carotenoid content did not show significant change in different concentrations of cadmium. Malon De Aldehyde content, Antocyanin content, total Phenol and Flavonoid significantly increased under 900 μM cadmium concentration. Total protein content was significantly decreased in 900 μM Cd concentration while, Phenylalanine ammonia lyase, Glutathione reductase and Ascorbate peroxidases activity enzyme were significantly increased in this level. Results confirmed that this medical plant have different physiological and biochemical mechanisms to reduce toxicity damage of cadmium. Evaluation of cadmium ion concentration in leaves and root showed that most cadmium was concentrated in leaves while; small amount of Cd was in the roots. These results showed that silybum marianum could be an appropriate plant for phytoremediation purposes.