Studies On Effects Of La On The Growth Of Rice Seedlings Under Stress

Through the experiments on La³⁺, this paper made a research on the influences of the rare earth element lanthanum on the sprout of the seeds of rice and the growth of the seedlings. And on the basis of the above research, with 10mg·L^-1 La³⁺ as the biological regulator and through the nourish liquid cultivating experiment, further researches were made on the influences of lanthanum on the physiology , the bio-chemistry and the growth index of the seedlings of rice under stress (heavy metals , salts and acid rains) . Thus discussions were made on the protecting effect of the rare earth on crops under stress. The results of those researches will provide powerful evidences to the decision on the safety density of the rare earth element applied to agriculture, and the proper solution to relieve the harmful effect on crops caused by the polluting threat such as heavy metals, salts and acid rains. Main achievements are as follows: 1. In a range of concentration (1 mg·L^-1～20 mg·L^-1), La³⁺ increased seed vigor, activity of proteinase,amylase and lipase, promoted the growth of plant shoots and roots. Optimal effect happened in the treatment of 10 mg·L^-1 La³⁺. The seeds germination and seedlings growth were restrained when concentrations were over 30 mg·L^-1 La³⁺. 2. The effect of the lanthanum on the roots was much more apparent than that on the shoots. The sensitivities of enzymes to La³⁺ were: proteinase> lipase> amylase. 3. While the rice seedling grew normally, the treatment of lanthanum increased activities of protecting enzymes (superoxide dismutase--SOD, catalase--CAT ) , reduced levels of lipid peroxidantion malondialdehyde (MDA) and cell membrane permeability, raised roots activity and chlorophyll content, thus improved the growth of rice seedlings. 4. 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 seedlings, increased roots activity and chlorophyll content of rice seedlings during the initial stage under stress of heavy metals (copper and cadmium) . However, with extending of the stress and increase of heavy metals concentration, the effects of lanthanum were reduced, even in synergy with heavy metals. 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. 5. For the seedlings of rice under the stress of salts and acid rains, lanthanum could improve the activities of protecting enzymes (superoxide dismutase--SOD, catalase--CAT), decreasecontent of malondialdehyde(MDA) and praline(Pro), and the penetrability of cell membrane, raise the content of chlorophyll in the leaves and the ratio of a/b in chlorophyll, improve roots activity in rice seedlings, then promoted the growth rice seedling under stress. The relieving function of La on the threats of salts and acid rains had relation with the density of salts and the acid of acid rains. La's relieving function would disappear if there was too much salt and acid. 6. The possible defense mechanism of rare earth elements lanthanum on the growth of rice seedlings under 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.