Study of cadmium contamination and its effects on some physiological and nutritional factors on alfalfa plants

Introduction: Alfalfa is the most important forage plant in Iran as well as Zanjan province in which it is cultivated in soils contaminated by heavy metals like cadmium(Cd). Infected leaves of these plants can threaten the health of animals and ultimately human. Heavy metals are also among the most important and dangerous ecological contaminants because of their long maintenance and their resistance against decomposition by microorganisms and a high potential for being assimilated by plants then entering in the human food chain. Cadmium is one of the most poisonous heavy metals for plants. So in order to analysis the contamination potential of alfalfa plants which are planted in heavy metals like Cd contaminated fields in Zanjan province, a research project was performed to evaluate the rate of accumulation of Cd in alfalfa plants and its effects on some growth, nutritional biochemical and physiological traits.
Material and methods: Seeds of alfalfa (Medicago sativa L.) Hamedani cultivar, were cultured in pots containing perlite and half concentrations of Hoagland’s medium in a hydroponic condition. After three weeks, plantlets with enough growth were subjected to 0(control), 25, 50 and 100 mM concentrations of cadmium nitrate treatments. Then the growth indices such as: root and shoot length, root and shoot dry weight and nutritional traits like: Cd concentration, soluble proteins and sugars and chlorophylls contents at different parts of plants and also two antioxidant enzymes activity and proline and carotenoid contents as biochemical factors were being measured. This experiment was carried out based on randomized complete block design with 4 replications in a greenhouse condition.
Results and discution: Results showed that, shoot and root length and dry weight, the contents of chlorophylls a and b, soluble proteins and also the activity of catalase enzyme in treated plants were decreased at all Cd treatments. This decrease has an upward trend from 25 to 100 m Cd treatment for most of measured traits. The maximum decrease for all measured traits was observed at 100 m Cd treatment. However, the contents of carotenoids, proline, soluble sugars and the activity of peroxidase enzyme were increased in Cd treated plants. The activity of peroxidase enzyme at 100 m Cd treatment increased 1.51 and 1.97 times more than that of control plants in shoot and root respectively. The accumulated amount of Cd in roots of treated plants was much higher than that of shoots.
Conclusion: Generally, it can be concluded that: contamination of alfalfa plants by Cd leads to severe decrease of its growth and nutritional indices specially its protein and chlorophyll contents. Although the negative effects of Cd have been relatively moderated in treated plants by increasing of peroxidase activity and proline and carotenoids contents however, the considerable amounts of Cd have been penetrated from root to shoot which is very harmful ecologically. Also decreasing of total soluble proteins among with increasing of soluble sugars and proline showed a considerable decrease in nutritional indices of Cd contaminated alfalfa plants. So consuming of alfalfa plants which are cultivated in Cd contaminated fields by livestock animals is not advised.