Response of photosynthetic characteristics and non-structural carbohydrate accumulation of Betula ermanii seedlings to drought stress.

We explored the effects of drought stress on photosynthetic characteristics and non-structural carbohydrate (NSC) accumulation of the timberline tree species Betula ermanii in Changbai Mountain with a drought control experiment. The results showed that drought significantly reduced the net photosynthetic rate and stomatal conductance, but increased water use efficiency (WUE) of B. ermanii seedlings. Drought dramatically improved the contents of soluble sugar and total NSC in leaves, barks, stems, and roots of B. ermanii seedlings, but significantly reduced their starch content. The stomatal conductance, photosynthetic rate and WUE decreased rapidly as the drought continued, whereas the contents of soluble sugar, starch and NSC increased and then declined. At the end of the experiment, 90% of the leaves turned yellow, and the ratios of soluble sugar to starch in the stems, barks and roots under the drought treatment were significantly higher than those in the control. These results demonstrated that B. ermanii might be a drought-avoidance species that could reduce water loss by rapidly reducing stomatal conductance and improving WUE under drought stress. B. ermanii might have evolved priority storage strategy to cope with water deficit through improving the content of soluble sugar in organs and increasing the transformation rate between starch and sugar. With the extension of drought stress, seedlings tended to die, since water stress might exceed the threshold of the plant self-regulation capacity. However, the content of NSC in organs did not decrease, suggesting that the death of B. ermanii under drought stress might not be caused by carbon starvation.

[Study of adherence of normal oral bacteria on polymethyl methyacrylate containing silver-supported silicate inorganic antibacteria].

OBJECTIVE: To study the oral normal bacteria adherence on polymethyl methyacrylate (PMMA) containing silver-supported silicate inorganic antibacterial, and the growth inhibitory concentration of silver-supported silicate inorganic antibacterial to normal oral bacteria were also investigated. METHODS: A certain volume of normal oral bacteria was inoculated on the RHI plate containing different dilution of silver-supported silicate inorganic antibacterial, then the growth of the bacteria was investigated by light microscope and biochemical methods; the oral bacteria plaque model in vitro was used to evaluate the adherence of 4 species normal oral bacteria mixture on the surface of PMMA which containing silver-supported silicate inorganic antibacterial in the proportion of 5% or 10%. RESULTS: The growth of normal oral bacteria was inhibited effectively by silver-supported silicate inorganic antibacterial within the concentration of 8%, and the growth of Porphyromonas gingivalis and Conclida albicans were inhibited at concentration from 1.25% to 2.50%, but the PMMA containing silver-supported inorganic antibacterial could not prevent the adherence of bacteria within a period of 16 days. CONCLUSION: Silver-supported silicate inorganic antibacterial has effectiveness on inhibiting the growth of normal oral bacteria, but could not prevent the adherence of oral normal bacteria mixture.

Mesostructured tin oxide as sensitive material for C(2)H(5)OH sensor.

Mesostructured tin oxide with high specific surface area was synthesized using cationic surfactant (cetyltrimethylammonium bromide, CTAB: CH(3)(CH(2))(15)N(+)(CH(3))(3)Br(-)) as the organic template and hydrous tin chloride (SnCl(4).5H(2)O) and NH(4)OH as the inorganic precursors under acidic conditions at ambient temperature. Thermogravimetric analysis (TGA), Fourier transformed infrared (FTIR), X-ray diffraction analysis (XRD), X-ray photoelectron spectrum (XPS) and N(2)-sorption isotherms were used to characterize the mesostructured tin oxide that was formed at room temperature as well as calcined at different temperature. The surface area of mesostructured tin oxide calcined at 400 degrees C is 136 m(2) g(-1). The indirect heating sensor using this material as sensitive body was fabricated on an alumna tube with Au electrodes and platinum wires. Electrical and sensing properties of such a sensor were investigated. It was found that the mesostructured tin oxide with high surface area had higher sensitivity to C(2)H(5)OH and selectivity to gasoline than commercial sample of polycrystalline tin(IV) oxide.