Search

Clonal propagation of superior genotypes of commercially important forest trees via somatic embryogenesis has been hindered by a general inability to initiate embryogenic cultures from tissues of mature trees. We tested staminate inflorescences of sweetgum (Liquidambar styraciflua L.) as a source of cells that might be redetermined from theirdifferentiated state to an embryogenic state. Buds containing staminate inflorescences were collected from seven sweetgum clones at varying stages of elongation prior to and continuing through bud break. Inflorescence tissues were cultured on medium containing thidiazuron (TDZ) alone or in combination with 2,4-D. Although most cultures were lost to contamination or killed by disinfestation treatments, the least expanded inflorescences from buds of one clone produced eight independent embryogenic cultures following culture on 0.01--1 mg/L TDZ, either continuously or as a 1-week pulse followed by transfer to basal medium. Repetitive embryogenesis continued on medium containing 0.01 mg/L TDZ. While most embryos were malformed, embryos from two of the clones germinated on basal medium lacking casein hydrolysate, and germinants from one of these converted to plantlets that were acclimatized to greenhouse conditions. These preliminary results indicate that tissues from inflorescences of mature sweetgum trees have the abilityto produce embryogenic cultures, thus providing a potential route for large-scale cloning of superior genotypes. [ABSTRACT FROM AUTHOR]

Methylmercury is a highly toxic, organic derivative found in mercury-polluted wetlands and coastal sediments worldwide. Though commonly present at low concentrations in the substrate, methylmercury can biomagnify to concentrations that poison predatory animals and humans. In the interest of developing an in situ detoxification strategy, a model plant system was transformed with bacterial genes (merA for mercuric reductase and merB for organomercurial lyase) for an organic mercury detoxification pathway. Arabidopsis thaliana plants expressing both genes grow on 50-fold higher methylmercury concentrations than wild-type plants and up to 10-fold higher concentrations than plants that express merB alone. An in vivo assay demonstrated that both transgenes are required for plants to detoxify organic mercury by converting it to volatile and much less toxic elemental mercury.

Methylmercury is an environmental toxicant that biomagnifies and causes severe neurological degeneration in animals. It is produced by bacteria in soils and sediments that have been contaminated with mercury. To explore the potential of plants to extract and detoxify this chemical, we engineered a model plant, Arabidopsis thaliana, to express a modified bacterial gene, merBpe, encoding organomercurial lyase (MerB) under control of a plant promoter. MerB catalyzes the protonolysis of the carbon---mercury bond, removing the organic ligand and releasing Hg(II), a less mobile mercury species. Transgenic plants expressing merBpe grew vigorously on a wide range of concentrations of monomethylmercuric chloride and phenylmercuric acetate. Plants lacking the merBpe gene were severely inhibited or died at the same organomercurial concentrations. Six independently isolated transgenic lines produced merBpe mRNA and MerB protein at levels that varied over a 10- to 15-fold range, and even the lowest levels of merBpe expression conferred resistance to organomercurials. Our work suggests that native macrophytes (e.g., trees, shrubs, grasses) engineered to express merBpe may be used to degrade methylmercury at polluted sites and sequester Hg(II) for later removal.

We examined the ability of yellow poplar (Liriodendron tulipifera) tissue cultures and plantlets to express modified mercuric reductase (merA) gene constructs. Mercury-resistant bacteria express merA to convert highly toxic, ionic mercury, Hg(II), to much less toxic, elemental mercury, Hg(O). Expression of merA in transgenic plants might provide an ecologically compatible approach for the remediation of mercury pollution. Because the alteration of the bacterial merA gene sequence is necessary for high-level expression in Arabidopsis thaliana, yellow poplar proembryogenic masses (PEMs) were transformed with three modified merA constructs via microprojectile bombardment. Each construct was synthesized to have altered flanking regions with increasing amounts of modified coding sequence. All merA constructs conferred resistance to toxic, ionic mercury in independently transformed PEM colonies. Stability of merA transgene expression increased in parallel with the extent of gene coding sequence modification. Regenerated plantlets containing the most modified merA gene (merA18) germinated and grew vigorously in media containing normally toxic levels of ionic mercury. The merA18 plantlets released elemental mercury at approximately 10 times the rate of untransformed plantlets. These results indicate that plants expressing modified merA constructs may provide a means for the phytoremediation of mercury pollution.

The autumn of 1994 has arrived. At this same time last year, most political pundits and policy wonks proclaimed that the Congress would surely take action to overhaul the American health care system before this year's November elections. But as 1994 draws to a close, it has become apparent that Washington is unlikely to produce comprehensive reform legislation at any time in the near future. However, while our political system has failed to act in any meaningful way, its inability to chart a course for change has not quelled the movement to reshape our nation's health care system. Despite Congressional inertia, substantial health care reform is taking place both in Michigan and throughout the nation. These reforms are characterized by a central theme: rapid movement away from our historic focus on illness, and toward a more rational focus on health. Our commitment to healthy communities stands as a firm testament to our mission of service and our role as the central core of the health care delivery system. This article will address the various components of that paradigm shift, and highlight some of the outstanding efforts of Michigan hospitals as they partner with their communities to reshape the delivery of health care services.