Changes in growth, physiological and biochemical characteristics under salt stress with or without La 3+ treatment in Saussurea involucrata Kar. et Kir. were investigated. The results showed that La 3+ relieved the plant growth inhibition, improved the leaf water potential and water content, increased the soluble protein and the proline contents and decreased malondialdehyde content under salt stress. Further, addition of La 3+ significantly increased the activities of superoxide dismutase, ascorbate peroxidase, catalase, and glutathione reductase, decreased the photosynthetic pigment decomposition and increased the ratio of total chlorophyll to carotenoids under salt stress.Additional key words: antioxidative enzymes, carotenoids, chlorophyll, growth, leaf water potential, proline, proteins.
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Saussurea involucrataKar. et Kir. is an endangered medicinal plant growing in the Tianshan and Kunlun mountain ranges of China, and is very sensitive to salinity stress. High salinity causes both water stress and ionic toxicity, which disputes the various enzymes, function of photosynthetic apparatus and many other processes and severely affects yield and quality of this medicinal plant (Chen et al. 1999). It is well known that rare-earth elements form a special group and have interesting effects on plant growth (He and Loh 2000, Ouyang et al. 2003). Lanthanum is a rare-earth element and can relieve oxidative damage in plants exposed to a variety of environmental stresses (Gao and Chen 2005, Shi and Chen 2005, Wei et al. 1997). Feng et al. (1999 reported that La 3+ could alleviate the decrease of osmotic potential, increase the content of proline and reduce the accumulation of MDA under osmotic stress in the leaves of maize seedlings. There is salt stress affecting the growth of S. involucrata in saline area. Up to now, there is few reports on the role of La 3+ in alleviating the oxidative damage in this plant under salt stress. So, study on this may improve the endangered plant growth and production. In the present study, the effect of La 3+ on oxidative damage in S. involucrata under salt stress was investigated. The investigation also goes in some way towards studying the effects of La 3+ on plant growth, soluble protein content and photosynthetic pigments in this species in response to salinity stress.Seeds of Saussurea involucrata Kar. et Kir. were surface-disinfested and aseptically planted into Vermiculite, then they were irrigated with liquid NaCl solution at different concentrations (0, 20, 50 and 100 mM) on 0, 5 th , 10 th and 15 th day. The 15-d-old germinated seedlings were divided into two groups. Previous reports indicated that 0.1 mM La 3+ was more suitable concentration for alleviating environment stress (Pang et al. 2002. So, in this experiment, treatment group seedlings under varying salinity stress were sprayed with 100 cm 3 0.1 mM La(NO 3 ) 3 . 6 H 2 O solution once a day for five consecutive days. The control group seedlings under varying salinity stress were sprayed with the same volume water. The...