Mercury detoxification with transgenic plants and other biotechnological breakthroughs for phytoremediation

Summary Phytoremediation, or the use of plants for removal and detoxification of environmental pollutants, has garnered great attention in recent years. This heightened interest is both scientifically, due the fascinating processes utilized by plants for tolerance and removal of harmful compounds, and commercially, as plants represent a more environmentally compatible and less expensive method of site remediation compared to standard approaches. The majority of phytoremediation studies have been with naturally occurring plant species after empirical discovery of their exceptional abilities for such applications. This has led to a growing body of literature and wider acceptance for plants in many aspects of environmental rehabilitation. However, this has occurred with little understanding of their basic biological mechanisms of action or investigation of alternative strategies for enhancing the capabilities of these extraordinary plants. Better understanding of plant physiology, biochemistry and molecular biology in response to specific contaminants is critical for optimization and advancement of phytoremediation. By applying the tools of biotechnology, the potential for plants as an aggressive method of environmental decontamination may be realized. This paper will serve as an introduction to the first Symposium assembled exclusively to review the use of molecular genetic and biotechnological methods for improvement of plants for phytoremediation. After a brief review of the other invited speakers' works (with more extensive papers following), the pioneering work using bacterial genes expressed in plants for removal of mercurial compounds will be surveyed.     

Localization of Shiga toxin gene in the region of Shigella dysenteriae 1 chromosome specifying virulence functions

Abstract R' plasmids have been generated that contain a determinant of Shigella dysenteriae 1 which directs the synthesis of Shiga toxin in Escherichia coli K-12. This gene is closely linked to the argE locus and thus is located in a region of the Shigella chromosome known to contain determinants of virulence factors.     

Mechanism of mitochondrial DNA replication in mouse L-cells: introduction of superhelical turns into newly replicated molecules

The first closed circular product of mouse L-cell mitochondrial DNA synthesis is a zero superhelix density molecule. Both of the asynchronously synthesized mitochondrial DNA daughter molecules pass through the zero superhelix density state. These molecules have a mean lifetime of approximately one hour before conversion to supercoiled molecules containing approximately 100 superhelical turns. A low frequency of intermediates in the conversion of these two closed circular forms is demonstrable by agarose gel electrophoresis. The degree of sensitivity to alkali has been used to demonstrate that newly replicated mitochondrial DNA has the same content of ribonucleotides as mass-labeled mitochondrial DNA.     

DNA primase of human mitochondria is associated with structural RNA that is essential for enzymatic activity

DNA primase isolated from human mitochondria sediments in glycerol density gradients at 30S and 70S. These unusually high sedimentation coefficients are a result of association of the primase activity with RNA. Treatment of primase with nuclease not only affects its sedimentation behavior, but also inactivates the primase activity. The major RNA species that cofractionates with primase activity is shown by direct sequence analysis to be cytosolic 5.8S ribosomal RNA (rRNA). Specific degradation of endogenous 5.8S rRNA using ribonuclease H and oligonucleotides complementary to 5.8S rRNA results in reduction of primase activity. Other small RNAs may play a structural role in the formation of an active DNA primase complex.