Physiological and proteolytic activities of Medicago truncatula under different cadmic treatments

Medicago truncatula (A17) were cultivated under strictly controlled growth conditions, in a nutrient solution in the absence or presence of Cd (10, 20 and 50 μM CdSO₄). After 20 days, decrease on the plant growth was detected and chlorosis appeared on the foliar limbs. Root growth, relative root growth (Cd -treated/untreated seedlings) and tolerance index (difference of root growth between Cd-treated and untreated seedlings) were considered as the indices of tolerance to this toxic metal. The results showed that the internal quantity of cadmium increases essentially in roots level with the elevation of the cadmium concentration in the growth medium. Different cadmium treatments significantly and considerably decreased shoot growth and root growth at Cd concentration 20μM. In addition, cadmium induced the proteolytic activity endopeptidase in roots. The increase of calcium, magnesium and potassium content in plant tissues in response to different Cd treatments reflected a kind of adaptive mineral strategy that apparently failed to give resistance to M. truncatula plant against Cd treatments.