基于3S的黄土高原北部土地沙化分析——以陕西省神木县为例

采用实地调查和遥感数据分析相结合的方式,分析黄土高原北部神木县的土地沙化变化趋势及社会背景因素,为草地沙化的有效遏制提供依据。结果表明,神木县的土地沙化呈“整体缩小局部扩展”趋势。1986-2004年,沙化土地面积减少了10%（750 km2）。土地沙化在地区间有很大差异,县西北部乡镇里沙化土地减少明显,而南部的黄土峁地区沙化土地有所增加。与社会统计资料对比分析后发现,耕地面积比例大、人均土地面积少的乡镇地区,土地沙化趋势明显。以上结果意味着农田利用对黄土峁地区土地沙化有很大影响,传统耕作方式的改变有助于遏制土地沙化。     

Bean husks as a supplemental fiber for ruminants: Potential use for activation of fibrolytic rumen bacteria to improve main forage digestion

This study evaluated the suitability of easily digested fiber sources as a supplemental fiber to improve overall fiber digestion in ruminants. First, the degradation of five fibrous feedstuffs and the stimulatory effects on rumen bacteria were examined in situ. Chickpea and lablab bean husks were selected for their potential use due to their large degradable fraction (> 94%), which had a stimulatory effect on fibrolytic rumen bacteria such as Fibrobacter succinogenes. Second, a possible improvement in the digestibility of rice straw diet by husk supplementation was monitored in vivo. Four dietary treatments comprising RS (rice straw and concentrate), CHM (RS supplemented with Myanmar chickpea husk), CHE (RS with Egyptian chickpea husk) and LH (RS with lablab bean husk) were allocated to four wethers. The digestibility of acid detergent fiber was 3.1–5.5% greater in CHM and LH than RS. Total volatile fatty acid concentration was higher in LH than other treatments. Acetate proportion was higher in LH than RS. Ruminal abundance of F. succinogenes was 1.3–1.5 times greater in CHM and LH than RS. These results suggest that bean husk supplementation, especially lablab bean husk, might improve the nutritive value of rice straw diet by stimulating fibrolytic bacteria.     

Differential safening activity of dymron and fenclorim on pretilachlor injury in rice seedlings in soil

The safening activity of dymron [1-(α,α-dimethylbenzyl)-3-( p -tolyl)urea] and fenclorim [4,6-dichloro-2-phenylpyrimidine] on the phytotoxic activity of pretilachlor [2-chloro-2',6'-diethyl- N- (2-propoxyethyl)acetanilide] on rice seedlings was examined in both water and soil culture. The safening activity of fenclorim in water culture was greater than that of dymron, whereas the activity of fenclorim in soil was lower than that of dymron. The fenclorim concentration in soil water was lower than that of dymron at all times when determined after the application at the same concentrations. The phytotoxic activity of pretilachlor and the safening activities of dymron and fenclorim were well correlated with the concentration of each in soil water but not with the amount in total soil. The adsorption of fenclorim on soil solids was greater than those of dymron and pretilachlor. It was suggested that both the phytotoxic activity of pretilachlor and the safening activities of dymron and fenclorim were dependent on their concentrations in soil water, which were primarily dominated by the adsorption on soil.     

Partial characterization of structure and function of a xylanase gene from the rumen hemicellulolytic bacterium Eubacterium ruminantium

A gene encoding for xylanase activity in the rumen hemicellulolytic bacterium Eubacterium ruminantium was cloned into pBR322 in Escherichia coli (E. coli ). The primary clone had a 5.7 kb insert produced by Eco RI partial digestion. Subcloning followed by sequencing allowed for the discovery that this enzyme has a glycosyl‐hydrolase family 10 catalytic domain with a family 9 carbohydrate binding module at C‐terminus and a region partially homologous to a family 22 carbohydrate binding module at N‐terminus. Cloned xylanase is specifically active against xylan and oligoxyloside to produce xylobiose and xylotriose, showing optimal pH and temperature at 7.0 and 50°C, respectively. Molecular size of the xylanase (91 kDa) was confirmed by zymogram analysis of the E. coli clone, which agreed with the predicted size from the DNA sequence. Functions of the two modules at C‐ and N‐termini were evaluated by using xylanase variants with and without the respective module and the C‐terminal module was found to be functional in binding to acid‐swollen cellulose and insoluble oat‐spelt xylan, whereas the N‐terminal module was inactive for binding them.     

Ruminal distribution of the cellulolytic bacterium Fibrobacter succinogenes in relation to its phylogenetic grouping

To investigate the ecological importance of the cellulolytic bacterium Fibrobacter succinogenes in fiber digestion, ruminal distribution of F. succinogenes was determined in relation to its phylogenetic grouping. Rumen digesta from wethers and steers fed orchardgrass hay, rice straw or fresh orchardgrass were employed as the materials for the analyses. Orchardgrass hay stem incubated in the rumen was also used. By using total DNA extracted from these materials, population sizes of total F. succinogenes and of four different phylogenetic groups of this species were quantitated through competitive polymerase chain reaction (PCR), and restriction fragment length polymorphism analysis of PCR products targeted the bacterial 16S rDNA. Rumen digesta and ruminally incubated hay stems had a reasonably high population size of F. succinogenes (×10^7?8/g) that was composed of strains belonging to the phylogenetic groups 1 and 3. The relative abundance of each group was different among the samples; group 1 dominated on the ruminally incubated hay stem and in the rumen of wethers fed fresh orchardgrass, while group 3 was major in the rumen of wethers and steers on hay diet. These results suggest that there could be phenotypic differences among the phylogenetic groups of F. succinogenes, and group 1 dominating on hay stem might contribute to rumen fiber digestion more than the other groups.     

Functional indispensability of fibronectin associated on the mesenchymal cell surface during the early period of feather development in the chick embryo in vitro

To clarify the role of fibronectin (FN) during the early period of feather development, reconstituted skin consisting of intact epithelium and isolated mesenchymal cells from embryonal chick skin was used. In early feather development, FN was localized around mesenchymal cells of the dermal condensation. Isolated mesenchymal cells had associated with FN on their surfaces. FN on the cell surface dissociated following EDTA treatment, and EDTA‐treated cells re‐associated with exogenous FN. The intact epithelium also bound to exogenous FN at the placode. When FN‐associated or FN‐reassociated mesenchymal cells were used, the reconstituted skin formed feather rudiments only at the positions where the epithelial placode existed originally, and the locality of tenascin transferred from the placode to the mesenchyme during the period of feather bud formation. However, in reconstituted skin using FN‐dissociated mesenchymal cells, feather rudiments did not form. Additionally, the epithelial placodes disappeared, and tenascin was distributed uniformly on the surface of the epithelium and not localized in the mesenchyme. These findings suggest that FN associated on the surfaces of mesenchymal cells maintains the functions of mesenchymal cells as dermal condensation and mediates epithelial‐mesenchymal interactions during the early period of feather development. The results also suggest that reconstituted skin is a useful tool for functional studies on the extracellular matrix.     

Reduced intake of dietary lysine promotes accumulation of intramuscular fat in the Longissimus dorsi muscles of finishing gilts

The present study was conducted to elucidate the effect of dietary lysine levels on the intramuscular fat (IMF) content in the Longissimus dorsi (L. dorsi) muscles of finishing gilts. Eleven gilts in total from two litters of pigs aged 110 days were used. The average initial bodyweight of the pigs was 61.7 kg. Six pigs were assigned to the low lysine (LL) diet group (lysine content: 0.43 or 0.40%) and five pigs were assigned to the control group (lysine content: 0.65 or 0.68%). The diets were iso‐energetic and iso‐protein, and contained all essential amino acids (apart from lysine) in the recommended amounts. The pigs were fed these diets until their live weights reached 110 kg. Live weight gain and feed efficiency tended to be lower in the LL group (P = 0.118 and P = 0.052, respectively). Pigs from the LL group took 5 days longer to reach 110 kg (P < 0.01). The IMF content in the L. dorsi of the LL group was twice as high as that of the control group (6.7 vs 3.5%; P < 0.01). The percentage of oleic acid in the L. dorsi of the LL group tended to be higher than that of the control group (P = 0.052), whereas the percentage of linoleic acid and the total percentage of polyunsaturated fatty acids in the L. dorsi were lower (P < 0.05) in the LL group. Free L‐carnitine content in the L. dorsi was lower (P < 0.05) in the LL group. The average abundance of peroxisome proliferator‐activated receptor gamma mRNA in the L. dorsi of the LL group was threefold higher than that of the control group. The leptin mRNA abundance in the L. dorsi of the LL group was 3.3‐fold higher than that of the control group (P < 0.01). These results suggest that a higher activity of adipogenesis may have been involved in the promoted accumulation of IMF in the L. dorsi muscles of pigs, induced by a dietary LL level.     

Inclusion of novel bacteria in rumen microbiology: Need for basic and applied science

Rumen microbiology has made a significant contribution to the understanding of ruminant nutrition. However, further progress in research has been hindered by the incomplete analysis of the rumen microbiota comprised of bacteria, protozoa and fungi, most of which remain uncharacterized due to the difficulties in their isolation and cultivation. In order to maximize rumen fiber digestion, it is necessary to understand the community structure of rumen microbes, especially bacteria, and the factors that influence their composition. Recent advances in molecular biology techniques allow the analysis of such bacteria without cultivation, thereby identifying many functional, but uncultured, bacteria as new targets for basic and applied research. Specific uncultured bacterial groups are being considered as important members of a fibrolytic consortium in the rumen, judging by their ecologic distribution. The inclusion of such uncharacterized bacteria in analyses is crucial for understanding the rumen microbial community and its manipulation. In addition, these bacteria could potentially be candidates as probiotics and sources of enzymes for animal feed and other industrial uses.     

Ecological characterization of three different phylogenetic groups belonging to the cellulolytic bacterial species Fibrobacter succinogenes in the rumen

To study the group‐dependent ecology of Fibrobacter succinogenes in the rumen, real‐time polymerase chain reaction assays for two phylogenetic groups (groups 2 and 3) of F. succinogenes were newly established and applied to rumen samples. Both the assays targeting the bacterial 16S rDNA were sensitive and accurate, showing wide quantifiable ranges (10⁴?10⁹ and 10²?10⁹ copies of 16S rDNA) and high recoveries of known amounts of added DNA (96.9 and 98.0%). The quantity of group 1 was confirmed to be numerable by subtracting assay values of groups 2 and 3 from that of F. succinogenes species (groups 1–3). By using the developed assays and the above subtractive calculation, the quantities of all three groups were evaluated in solid and liquid fractions of the rumen content and also on hay stems. In the solid fraction, groups 1 and 2 were abundantly present, compared with group 3 (P < 0.05). On untreated hay stems, group 1 was dominant throughout 48 h. In addition, group 1 showed growth even on the cellulase‐treated hay stems, unlike the other two groups. These results suggest that F. succinogenes group 1 greatly contributes to rumen fiber digestion, even for less degradable materials.     

Production of transgenic cloned pigs expressing the far-red fluorescent protein monomeric Plum

Monomeric Plum (Plum), a far-red fluorescent protein with photostability and photopermeability, is potentially suitable for in vivo imaging and detection of fluorescence in body tissues. The aim of this study was to generate transgenic cloned pigs exhibiting systemic expression of Plum using somatic cell nuclear transfer (SCNT) technology. Nuclear donor cells for SCNT were obtained by introducing a Plum-expression vector driven by a combination of the cytomegalovirus early enhancer and chicken beta-actin promoter into porcine fetal fibroblasts (PFFs). The cleavage and blastocyst formation rates of reconstructed SCNT embryos were 81.0% (34/42) and 78.6% (33/42), respectively. At 36–37 days of gestation, three fetuses systemically expressing Plum were obtained from one recipient to which 103 SCNT embryos were transferred (3/103, 2.9%). For generation of offspring expressing Plum, rejuvenated PFFs were established from one cloned fetus and used as nuclear donor cells. Four cloned offspring and one stillborn cloned offspring were produced from one recipient to which 117 SCNT embryos were transferred (5/117, 4.3%). All offspring exhibited high levels of Plum fluorescence in blood cells, such as lymphocytes, monocytes and granulocytes. In addition, the skin, heart, kidney, pancreas, liver and spleen also exhibited Plum expression. These observations demonstrated that transfer of the Plum gene did not interfere with the development of porcine SCNT embryos and resulted in the successful generation of transgenic cloned pigs that systemically expressed Plum. This is the first report of the generation and characterization of transgenic cloned pigs expressing the far-red fluorescent protein Plum.