MoS presents a promising low-cost catalyst for the hydrogen evolution reaction (HER), but the understanding about its active sites has remained limited. Here we present an unambiguous study of the catalytic activities of all possible reaction sites of MoS, including edge sites, sulfur vacancies, and grain boundaries. We demonstrate that, in addition to the well-known catalytically active edge sites, sulfur vacancies provide another major active site for the HER, while the catalytic activity of grain boundaries is much weaker. The intrinsic turnover frequencies (Tafel slopes) of the edge sites, sulfur vacancies, and grain boundaries are estimated to be 7.5 s (65-75 mV/dec), 3.2 s (65-85 mV/dec), and 0.1 s (120-160 mV/dec), respectively. We also demonstrate that the catalytic activity of sulfur vacancies strongly depends on the density of the vacancies and the local crystalline structure in proximity to the vacancies. Unlike edge sites, whose catalytic activity linearly depends on the length, sulfur vacancies show optimal catalytic activities when the vacancy density is in the range of 7-10%, and the number of sulfur vacancies in high crystalline quality MoS is higher than that in low crystalline quality MoS, which may be related with the proximity of different local crystalline structures to the vacancies.

Site-specific heritable mutations in maize genes were engineered by introducing chimeric RNA͞DNA oligonucleotides. Two independent targets within the endogenous maize acetohydroxyacid synthase gene sequence were modified in a site-specific fashion, thereby conferring resistance to either imidazolinone or sulfonylurea herbicides. Similarly, an engineered green f luorescence protein transgene was site-specifically modified in vivo. Expression of the introduced inactive green f luorescence protein was restored, and plants containing the modified transgene were regenerated. Progeny analysis indicated Mendelian transmission of the converted transgene. The efficiency of gene conversion mediated by chimeric oligonucleotides in maize was estimated as 10 ؊4 , which is 1-3 orders of magnitude higher than frequencies reported for gene targeting by homologous recombination in plants. The heritable changes in maize genes engineered by this approach create opportunities for basic studies of plant gene function and agricultural trait manipulation and also provide a system for studying mismatch repair mechanisms in maize.

Zea mays transformants produced by particle bombardment of embryogenic suspension culture cells of the genotype A188 x B73 and selected on kanamycin or bialaphos were characterized with respect to transgene integration, expression, and inheritance. Selection on bialaphos, mediated by the bar or pat genes, was more efficient than selection on kanamycin, mediated by the nptII gene. Most transformants contained multicopy, single locus, transgene insertion events. A transgene expression cassette was more likely to be rearranged if expression of that gene was not selected for during callus growth. Not all plants regenerated from calli representing single transformation events expressed the transgenes, and a non-selectable gene (uidA) was expressed in fewer plants than was the selectable transgene. Mendelian inheritance of transgenes consistent with transgene insertion at a single locus was observed for approximately two thirds of the transformants assessed. Transgene expression was typically, but not always, predictable in progeny plants--transgene silencing, as well as poor transgene transmission to progeny was observed in some plant lines in which the parent plants had expressed the transgene.

R. 2001. The biology of Canadian weeds. 112. Ulex europaeus L. Can. J. Plant Sci. 81: 325-337. Gorse (Ulex europaeus L.) is a leguminous shrub native to western Europe and North Africa. During the past century it has greatly expanded its adventive range in Australia, New Zealand, Chile and Europe, and along the Pacific and Atlantic coasts of North America. In Canada, it is found in British Columbia (Vancouver, Vancouver Island, the Gulf Islands and Queen Charlotte Islands) where it is classed as a noxious weed. Gorse is also found from Virginia to Massachusetts on the east coast of North America. The shrub rapidly invades dry and disturbed areas, forming dense thickets that can suppress and inhibit native vegetation, including economically important conifer seedlings. It can occupy the same habitats as Scotch broom [Cytisus scoparius (L.) Link] but usually occurs on drier sites. Both of these legumes threaten native plant communities but U. europaeus persists longer and possesses conspicuous spines. Invasive characteristics of gorse include its evergreen habit, prolific seed production, longevity of seeds in the soil and nitrogen fixation. Human activities such as agriculture and construction of logging roads have accelerated the spread of gorse in British Columbia, but there is still an historic opportunity to restrict the population expansion that this species has exhibited in many other countries. Various methods of control (chemical, manual, biological and integrated) are evaluated. , mais il préfère habituellement des endroits plus secs. Ces deux légumineuses menacent les peuplements d'espèces indigènes, quoique la première persiste plus longtemps et présente des épines très évidentes. Parmi les caractéristiques qui font de l'ajonc d'Europe une plante envahissante, mentionnons un port semblable à celui des conifères, une production abondante de semences, la longévité des graines dans le sol et la capacité de fixer l'azote. Les activités humaines comme l'agriculture et la construction de chemins d'exploitation ont accéléré la propagation de l'ajonc d'Europe en Colombie-Britannique, mais on pourrait encore freiner son expansion, ce qui n'est plus le cas dans d'autres pays. Suit une évaluation de diverses méthodes de lutte (chimique, manuelle, biologique et intégrée).

No abstract