Ultrastructural Studies of Spermiogenesis of Conocephalus saltator (Saussure)

The acrosome of the spermatozoa is the organelle involved in its penetration through the ova membranes during the fertilization process. Several features of this process are considered to be related to the fertilization events e.g. some substance coats outside the membrane. During the maturation process the spermatozoa of Conocephalus saltator develop a coat of tubules and filaments which overly some membrane regions in a specific array. The mature spermatozoa are seen to adhere in these regions and form threads of 20 cells long and five to six wide. It is suggested that the external coat plays a role in this 'sticking' phenomenon.     

Mode of Action of Zorbamycin

Zorbamycin (U-30,604E) induces rapid degradation of deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) in Bacillus subtilis cells. DNA degradation is initiated first and is closely followed by the degradation of RNA. No interaction between isolated DNA and zorbamycin is observed. Nucleic acid and protein syntheses are not inhibited by zorbamycin in cell-free systems. Since the initial effect of the antibiotic is expressed at the level of the cellular DNA fraction, we assume that zorbamycin somehow induces a change in the structure or function of the cellular DNA fraction which results in rapid breakdown of this fraction.     

Responses of tropical cladocerans to a gradient of resource quality

1. The response of three tropical cladocerans to a gradient of resource quality was compared in a series of growth bioassays using seston collected from five lakes of different depth and trophic structure in Michigan, U.S.A. To assess the food quality in terms of digestibility, assimilation experiments were performed with ³²P‐labelled seston from the same lakes. Animals were also analysed for P‐content in their tissues at the end of these assays. 2. In general, assimilation efficiency was higher when animals fed on seston from shallow compared to deep lakes, and was significantly correlated with growth rates, suggesting that shallow lakes have the best food resources in terms of digestibility and P availability. 3. Results also showed that all cladoceran species responded similarly to the resource gradient, with lower growth rates in deep lakes and higher growth rates in shallow lakes, although the strength of response (sensitivity) was different among the species tested. 4. The cladoceran Moina micrura was the most sensitive species, and also displayed the highest P‐content and maximal growth rate, a pattern consistent with the growth rate hypothesis. 5. However, seston C : P ratio and growth rates in the different resources did not correlate with the animals’ P‐contents, showing an uncoupling between RNA‐phosphorus demands for growth and seston food quality. 6. In conclusion, our results support the idea that digestion resistance in algae is a major constraint to cladocerans in natural plankton communities.     

Seasonal and interannual variations in carbon dioxide exchange over a cropland in the North China Plain

In China, croplands account for a relatively large form of vegetation cover. Quantifying carbon dioxide exchange and understanding the environmental controls on carbon fluxes over croplands are critical in understanding regional carbon budgets and ecosystem behaviors. In this study, the net ecosystem exchange (NEE) at a winter wheat/summer maize rotation cropping site, representative of the main cropping system in the North China Plain, was continuously measured using the eddy covariance technique from 2005 to 2009. In order to interpret the abiotic factors regulating NEE, NEE was partitioned into gross primary production (GPP) and ecosystem respiration (R_eco). Daytime R_eco was extrapolated from the relationship between nighttime NEE and soil temperature under high turbulent conditions. GPP was then estimated by subtracting daytime NEE from the daytime estimates of R_eco. Results show that the seasonal patterns of the temperature responses of R_eco and light‐response parameters are closely related to the crop phenology. Daily R_eco was highly dependent on both daily GPP and air temperature. Interannual variability showed that GPP and R_eco were mainly controlled by temperature. Water availability also exerted a limit on R_eco. The annual NEE was ?585 and ?533 g C m^?2 for two seasons of 2006–2007 and 2007–2008, respectively, and the wheat field absorbed more carbon than the maize field. Thus, we concluded that this cropland was a strong carbon sink. However, when the grain harvest was taken into account, the wheat field was diminished into a weak carbon sink, whereas the maize field was converted into a weak carbon source. The observations showed that severe drought occurring during winter did not reduce wheat yield (or integrated NEE) when sufficient irrigation was carried out during spring.     

小鼠淋巴细胞抗原CTLA-4的胞外肽段表达及纯化

目的: 真核细胞表达小鼠淋巴细胞抗原CTLA-4胞外段肽,研究表达肽段与抗原呈递细胞B7分子结合后减轻小鼠淋巴细胞刺激后的增殖抑制,从而启动T淋巴细胞进一步增殖。方法:从小鼠脾脏淋巴细胞获得总RNA,通过逆转录PCR扩增出CTLA-4全长基因,克隆并测序。依据胞外段序列和真核表达载体pcDNA3.1序列,合成引物扩增胞外片段,两者经内切核酸酶处理、连接构建重组表达pcDNA3.1载体,重组质粒经测序验证后,采用lipofectamine 2000转染入小鼠肝癌细胞Hepa1-6,经G418筛选获得稳定表达细胞株。结果:获得小鼠CTLA-4胞外段真核表达载体和小鼠肝癌细胞Hepa1-6稳定表达转染细胞株,制备了CTLA-4胞外肽段,经His标签抗体和小鼠CTLA-4抗体Western blot检测表达蛋白带均呈阳性。结论:获得CTLA-4胞外段肽,为进一步研究该肽的作用打下基础。