[Effect of Water Extracts from Rhizosphere Soil of Cultivated Astragalus membranaceus var. mongholicus on It's Seed Germination and Physiological Characteristics].

OBJECTIVE: To explore the relationship between continuous cropping obstacle and autotoxicity of Astragalus membranaceus var. mongholicus. METHODS: Distilled water(CK), water extracts of rhizosphere soil(50, 100, 200 and 400 mg/mL) were applied to test their effect on early growth and physiological characteristics of Astragalus membranaceus var. mongholicus. RESULTS: The water extracts from rhizospher soil of cultivated Astragalus membranaceus var. mongholicus significantly increased seedling emergence rate, root length and vigor index of Astragalus membranaceus var. mongholicus seedling when at the concentration of 100 mg/mL or below, however,there was no significant effect at 200 mg/mL or higher. The water extracts from rhizosphere soil of cultivated Astragalus membranaceus var. mongholicus significantly reduced the SOD activity in Astragalus membranaceus var. mongholicus seedling at 400 mg/mL and POD activity at 200 mg/mL and 400 mg/mL,while significantly increased the MDA content. CONCLUSION: Water extracts from Astragalus membranaceus var. mongholicus rhizosphere soil significantly affected Astragalus membranaceus var. mongholicus germination and seedling growth in a concentration-dependent manner, generally, low concentrations increased the SOD and POD activity which improved seed germination and seedling growth, while high concentrations caused cell membrane damage of the seedling.

[Effect of drought stress on growth and physiological-biochemical characteristics of Stellaria dichotoma].

A pot experiment was conducted to study effect of drought stress on leaf physiological characteristics and growth of one year old Stellaria dichotoma seedlings. The result showed that plant height and shoot dry weight significantly decreased with decrease in soil water content; however, root length and root dry weight increased at light drought stress and decreased at severe drought stress. The result also showed that with the decrease of soil water content, proline content in S. dichotoma leaves decreased then increase, while solube protein content decreased. Activities of SOD and POD in S. dichotoma leaves significantly decreased as soil water content decreased, while activity of CAT significantly decreased at severe drought stress. Membrane permeability in S. dichotoma leaves increased, while MDA content decreased then increased as soil water decreased. These results suggest that S. dichotoma had osmotic stress resistance ability and reactive oxygen scavenging capacity at light drought stress, which caused S. dichotoma growth was no inhibited at a certain extent drought stress.

[Autotoxicity of aqueous extracts from plant of cultivated Astragalus membranaceus var. mongholicus].

OBJECTIVE: To exploring the relationship between continuous cropping obstacle and autotoxicity of Astragalus membranaceus var. mongholicus, autotoxic effect of plant aqueous extract were determined. METHODS: Distilled water (CK), aqueous extract of plant, including root, stem and leaf (12.5, 25, 50 and 100 mg/mL respectively)were applied to testing their effect on early growth of Astragalus membranaceus var. mongholicus. Specifically, seed germination rate, germination index, emergence rate, elongation of radical and embryo, and seedling vigor index were determined. RESULTS: The aqueous extract of root, stem, and leaf at 25 mg/mL significantly inhibited the seed germination and seedling growth of Astragalus membranaceus var. mongholicus, and this inhibitory effect generally increased with the increase of the concentration of aqueous extracts. To the comprehensive allelopathic effect, the extracts from Astragalus membranaceus var. mongholicus stem were more inhibitory than those from leaf and root. The germination index and seedling vigor index were more sensitive to extract than other determined parameters. CONCLUSION: Aqueous extracts from Astragalus membranaceus var. mongholicus plant gave inhibitory effects on Astragalus. membranaceus var. mongholicus germination and seedling growth, and this inhibitory effect generally increased with the increases of aqueous extract concentration at a certain ranges. In conclusion, there is an autotoxicity in continuous cropping of Astragalus membranaceus var. mongholicus.

[Construction and immunogenicity analysis of the attenuated recombinant Salmonella typhimurium strains expressing Echinococcus granulosus Eg95 antigen].

OBJECTIVE: To study the feasibility of using attenuated Salmonella typhimurium as carrier for oral immunization of Eg95 antigen of Echinococcus granulosus. METHODS: The recombinant plasmid pYA3341-Eg95 was constructed by inserting the Eg95 gene into expression vector pYA3341, and identified by the methods of PCR and enzyme digestion. The recombinant plasmid pYA3341-Eg95 was electro-transformed into attenuated S. typhimurium strains X3730 and X4550 one by one to construct the recombinant strain St-Eg95. The expression of recombinant Eg95 protein in the recombinant strains St-Eg95 was analyzed by Western blotting. The strains of St-Eg95 were passaged 10 times in vitro and the recombinant plasmids were extracted at one generation interval. The genetic stability of recombinant plasmids was identified by PCR. BALB/c mice were randomly divided into six groups (five mice per group) and inoculated orally with St-Eg95, 100 µl/mouse, at dosage of 1 x 10(9), 1 x 10(10), 1 x 10(11), and 1 x 10(12) cfu/ml, wild-type S. typhimurium strain(l x l0(7)cfu/ml), and PBS, respectively. The survival rate was monitored daily for 30 days. Another 15 mice were divided into three groups and inoculated orally with St-Eg95(5 x 10(5) cfu/ml), X4550(pYA3341)(5 x 10(5) cfu/ml), and PBS, respectively, for 2 times, 0.5 ml/mouse/time, at biweekly intervals. On weeks 0, 2, 4, and 6 after the second immunization, sera were collected and tested for the presence of Eg95 antibody titers using commercially Eg antibody detection ELISA kit. The splenic lymphocyte proliferation was detected by MTT assay at 6 weeks after the second immunization. RESULTS: The constructed recombinant plasmid pYA3341-Eg95 was identified by enzyme digestion and PCR identification. The Eg95 protein (M, 18000) was expressed in the recombinant strains St-Eg95. After the recombinant strains St-Eg95 were passaged 10 times, the Eg95 gene (about 486 bp) was still amplified from St-Eg95. Safety results showed that mice inoculated orally with the St-Eg95 or PBS were all survival on the 30th day after immunization. However, all mice taking wild virulent S. typhimurium strain diedr within 4 days. The Eg95-specific antibodies examined by indirect ELISA were significantly higher in mice immunized with St-Eg95 than that of mice immunized with X4550 (pYA3341) or PBS at 2 weeks after the second immunization (P<0.05). The average Eg95-specific antibody titers reached up to the highest value of 1:1700 in mice immunized with St-Eg95 at 4 weeks after the second immunization. The lymphocyte proliferation test showed that the stimulation index value was significantly higher(P<0.05) in mice immunized with the St-Eg95(reached up to 1.94±0.15) than that in mice immunized with X4550 (pYA3341) or PBS at 6 weeks after the second immunization. CONCLUSION: The recombinant oral attenuated S. typhimurium St-Eg95 was successfully constructed, and has a good safety and immunogenicity profile in mouse.