Effects of La on growth and some physiological characteristics of rice seedlings under Cd stress

The effects of 10 mg·L-1 La(NO3)3 on the activities of protecting enzymes (superoxide dismutase--SOD, catalase--CAT)、 content of malondialdehyde (MDA), permeability of cell membrane、chlorophyll content, roots activity, the growth of seedlings and the accumulation of cadmium in shoots and roots of rice (Oryza sativa L.) seedlings under stress of cadmium (two CdCl2 concentra- tions of 50 mg·L-1 and 100 mg·L-1 ) were evaluated by the nutrient solution culture experiment. Thus discussions were made on the protecting effect of the rare earth on crops under stress of heavy metals. The activities of superoxide dismutase (SOD) and catalase (CAT) , content of malondialdehyde (MDA) of the seedlings in different experiments were determined and calculated after 0, 3, 6, 9 days; Permeability of cell membrane、chlorophyll content、roots activity、the growth of seedlings and the accumulation of cadmium in shoots and roots of rice seedlings in different experiments were determined and calculated after 10 days. The results showed that the treatment of lanthanum enhanced the activities of protecting enzymes (superoxide dismutase--SOD, catalase--CAT), decreased content of malondialdehyde (MDA) and permeability of cell membrane in shoots and roots of rice seed- lings, increased roots activity and chlorophyll content of rice seedlings during the initial stage under stress of cadmium. However, with extending of the stress and increase of cadmium concentration, the effects of lanthanum were reduced, even in synergy with cadmium. Then cadmium inhibits the growth of rice seedlings more grievously. It implied that proper lanthanum concentration could be selected to enhance the cadmium tolerance abilities of rice seedlings, but this relieving function of lanthanum on the threats of cadmium had relation with the concentration of cadmium stress and time of cadmium stress. In addition, the patterns of cadmium accumulation in seedlings of rice were the accumulation in the root was larger than that in the parts above, and the accumulation of cadmium had an obvious dose-effect relation with the densities of the different disposing groups. The disposal of lanthanum didn’t reduce the quantity of cadmium in the roots above the earth of the seedlings of rice. All results indicated that the possible defense mechanism of rare earth elements lanthanum on the growth of rice seedlings under cadmium stress was as follows: to reduce the level of the active oxygen in the plants, to decrease the harm of the adverse threats on the membrane of the plants, to improve the content of chlorophyll and the activity of the roots, to promote the metabolism of the plants.