The typical steppe ecosystems in China are now being increasingly degraded due mainly toovergrazing. To determine the limiting nutrients is of significance in order to find out ways of successfullyrestoring the degrad...The typical steppe ecosystems in China are now being increasingly degraded due mainly toovergrazing. To determine the limiting nutrients is of significance in order to find out ways of successfullyrestoring the degraded steppe. In addition to field fertilization experiments, N:P stoichiometry is an alternative,but argumentative tool to study nutrient limitation. In this study, we used these two approaches to identifythe most limiting nutrient element at the species level. Furthermore, nutrient addition experimentprovides an effective means to test our hypothesis that N:P stoichiometry will remain constant becauserelatively narrow range of N:P ratio in tissues of the terrestrial plants is an important adaptive mechanismfor plants to survive on earth. For these purposes, we designed a field experiment to examine theresponses of biomass and N:P stoichiometry of the two dominant species -- Leyrnus chinensis (Trin.)Tzvel. and Carex korshinskyiKom. -- to N fertilization at rates of O, 5, 15, 30, 50 and 80 g NH4NO3.m-2.a-~in two adjacent sites, one being excluded animal grazing for 22 years (site A), and another being free ofgrazing for only two years (site B) before the experiment was carried out. No effects of N fertilization weredetected in the first year as reflected by the aboveground biomass and P concentrations of the twospecies. The regression analysis showed that N:P ratios of two species of both sites remained constant inthe second year. N fertilization significantly increased the N concentrations of two species in both years,while only significantly increased the P contents of the two species in the second year. N and P contentsof the two species were significantly correlated in all cases in 2001. Our results suggest that theL. chinensis was in short of N in site B while the growth of C. korshinskyi was limited by P in site A, andthere is a significant synergistic relationship between tissue N and P concentrations in 2001. Our hypothesiswas valid on the species level since N:P ratio of the two species remaine展开更多
AIM:To generate an adenoviral vector specifically targeting the EphA2 receptor(EphA2R) highly expressed on pancreatic cancer cells in vivo.METHODS:YSA,a small peptide ligand that binds the EphA2R with high affinity,wa...AIM:To generate an adenoviral vector specifically targeting the EphA2 receptor(EphA2R) highly expressed on pancreatic cancer cells in vivo.METHODS:YSA,a small peptide ligand that binds the EphA2R with high affinity,was inserted into the HI loop of the adenovirus serotype 5 fiber knob.To further increase the specificity of this vector,binding sites for native adenoviral receptors,the coxsackie and adenovirus receptor(CAR) and integrin,were ablated from the viral capsid.The ablated retargeted adenoviral vector was produced on 293T cells.Specifi c targeting of this novel adenoviral vector to pancreatic cancer was investigated on established human pancreatic cancer cell lines.Upon demonstrating specifi c in vitro targeting,in vivo targeting to subcutaneous growing human pancreatic cancer was tested by intravenous and intraperitoneal administration of the ablated adenoviral vector.RESULTS:Ablation of native cellular binding sites reduced adenoviral transduction at least 100-fold.Insertion of the YSA peptide in the HI loop restored adenoviral transduction of EphA2R-expressing cells but not of cells lacking this receptor.YSA-mediated transduction was inhibited by addition of synthetic YSA peptide.The transduction specificity of the ablated retargeted vector towards human pancreatic cancer cells was enhanced almost 10-fold in vitro.In a subsequent in vivo study in a nude(nu/nu) mouse model however,no increased adenoviral targeting to subcutaneously growing human pancreas cancer nodules was seen upon injection into the tail vein,nor upon injection into the peritoneum.CONCLUSION:Targeting the EphA2 receptor increases specificity of adenoviral transduction of human pancreatic cancer cells in vitro but fails to enhance pancreatic cancer transduction in vivo.展开更多
在田间条件下利用埋设玻璃滤纸包法研究了绿肥翻压后的分解规律及其翻压绿肥对烟叶品质的影响。结果表明,经过13周的分解,苜蓿中有机C的矿化率高达81%,N素矿化率为54%;黑麦草有机C的矿化率为63%,N素矿化率为22%。这些矿化N中约92%的N(苜...在田间条件下利用埋设玻璃滤纸包法研究了绿肥翻压后的分解规律及其翻压绿肥对烟叶品质的影响。结果表明,经过13周的分解,苜蓿中有机C的矿化率高达81%,N素矿化率为54%;黑麦草有机C的矿化率为63%,N素矿化率为22%。这些矿化N中约92%的N(苜蓿)和74%的N(黑麦草)是在翻压后的前6周释放的。在烟株的整个生长期内,由苜蓿释放的N素约为N 43 kg hm-2,为了防止后期N素供应过多而导致上部烟叶烟碱含量过高,苜蓿宜提前翻压并从总N肥施用量中扣除由苜蓿矿化出的N。黑麦草因N素含量低和N素矿化量少,整个生长季中约释放了N 10.5 kg hm-2的N素,所以在黑麦草生长量不大的情况下,可将黑麦草全部翻压并忽略其释放的N素。在没有减少化肥施用量的情况下,翻压苜蓿提高了上部烟叶中烟碱含量,降低了总糖和还原糖含量。而翻压黑麦草对烟叶中烟碱含量有所降低,总糖和还原糖含量适中,因而烟叶的品质得到了改善。展开更多
文摘The typical steppe ecosystems in China are now being increasingly degraded due mainly toovergrazing. To determine the limiting nutrients is of significance in order to find out ways of successfullyrestoring the degraded steppe. In addition to field fertilization experiments, N:P stoichiometry is an alternative,but argumentative tool to study nutrient limitation. In this study, we used these two approaches to identifythe most limiting nutrient element at the species level. Furthermore, nutrient addition experimentprovides an effective means to test our hypothesis that N:P stoichiometry will remain constant becauserelatively narrow range of N:P ratio in tissues of the terrestrial plants is an important adaptive mechanismfor plants to survive on earth. For these purposes, we designed a field experiment to examine theresponses of biomass and N:P stoichiometry of the two dominant species -- Leyrnus chinensis (Trin.)Tzvel. and Carex korshinskyiKom. -- to N fertilization at rates of O, 5, 15, 30, 50 and 80 g NH4NO3.m-2.a-~in two adjacent sites, one being excluded animal grazing for 22 years (site A), and another being free ofgrazing for only two years (site B) before the experiment was carried out. No effects of N fertilization weredetected in the first year as reflected by the aboveground biomass and P concentrations of the twospecies. The regression analysis showed that N:P ratios of two species of both sites remained constant inthe second year. N fertilization significantly increased the N concentrations of two species in both years,while only significantly increased the P contents of the two species in the second year. N and P contentsof the two species were significantly correlated in all cases in 2001. Our results suggest that theL. chinensis was in short of N in site B while the growth of C. korshinskyi was limited by P in site A, andthere is a significant synergistic relationship between tissue N and P concentrations in 2001. Our hypothesiswas valid on the species level since N:P ratio of the two species remaine
基金Supported by Maurits en Anna de Kock fund to MA van Geer
文摘AIM:To generate an adenoviral vector specifically targeting the EphA2 receptor(EphA2R) highly expressed on pancreatic cancer cells in vivo.METHODS:YSA,a small peptide ligand that binds the EphA2R with high affinity,was inserted into the HI loop of the adenovirus serotype 5 fiber knob.To further increase the specificity of this vector,binding sites for native adenoviral receptors,the coxsackie and adenovirus receptor(CAR) and integrin,were ablated from the viral capsid.The ablated retargeted adenoviral vector was produced on 293T cells.Specifi c targeting of this novel adenoviral vector to pancreatic cancer was investigated on established human pancreatic cancer cell lines.Upon demonstrating specifi c in vitro targeting,in vivo targeting to subcutaneous growing human pancreatic cancer was tested by intravenous and intraperitoneal administration of the ablated adenoviral vector.RESULTS:Ablation of native cellular binding sites reduced adenoviral transduction at least 100-fold.Insertion of the YSA peptide in the HI loop restored adenoviral transduction of EphA2R-expressing cells but not of cells lacking this receptor.YSA-mediated transduction was inhibited by addition of synthetic YSA peptide.The transduction specificity of the ablated retargeted vector towards human pancreatic cancer cells was enhanced almost 10-fold in vitro.In a subsequent in vivo study in a nude(nu/nu) mouse model however,no increased adenoviral targeting to subcutaneously growing human pancreas cancer nodules was seen upon injection into the tail vein,nor upon injection into the peritoneum.CONCLUSION:Targeting the EphA2 receptor increases specificity of adenoviral transduction of human pancreatic cancer cells in vitro but fails to enhance pancreatic cancer transduction in vivo.
文摘在田间条件下利用埋设玻璃滤纸包法研究了绿肥翻压后的分解规律及其翻压绿肥对烟叶品质的影响。结果表明,经过13周的分解,苜蓿中有机C的矿化率高达81%,N素矿化率为54%;黑麦草有机C的矿化率为63%,N素矿化率为22%。这些矿化N中约92%的N(苜蓿)和74%的N(黑麦草)是在翻压后的前6周释放的。在烟株的整个生长期内,由苜蓿释放的N素约为N 43 kg hm-2,为了防止后期N素供应过多而导致上部烟叶烟碱含量过高,苜蓿宜提前翻压并从总N肥施用量中扣除由苜蓿矿化出的N。黑麦草因N素含量低和N素矿化量少,整个生长季中约释放了N 10.5 kg hm-2的N素,所以在黑麦草生长量不大的情况下,可将黑麦草全部翻压并忽略其释放的N素。在没有减少化肥施用量的情况下,翻压苜蓿提高了上部烟叶中烟碱含量,降低了总糖和还原糖含量。而翻压黑麦草对烟叶中烟碱含量有所降低,总糖和还原糖含量适中,因而烟叶的品质得到了改善。
