Split-root solution culture was used to study the promoting effect of lanthanum on rice (Oryza sativa) growth and its physiological mechanisms. Results sho w that low concentration (0.05～1.5 mg·L -1) increases rice yield an d grain numbers. High concentration depresses grain formation (9～30 mg·L -1 ) and root elongation (1.5～30 mg·L -1). No significant influence on str aw dry weight was found over the whole concentration range except the 0.05 mg·L -1 treatment. With the increase of La concentration from 0.05 to 0.75 mg· L -1, catalase (CAT) activity in the first fully expandeing leaves and root s decreases. When La concentration is greater than 0.75 mg·L -1 or less than 9 mg·L -1, it significantly decreases superoxide dismutase activity ( SOD) in the leaves and roots. No significant effects were found on chlorophyll, protein and malondialdehyde (MDA) content. Possible mechanisms of La′s promotin g effect on rice growth and reduction effect of ·O- 2 were discussed.
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