A New Laboratory Technique for Studying the Effects of Heavy Metals on Bryophyte Growth

A novel, non-destructive method for measuring moss gametophytegrowth rates is presented. Standard 2-cm moss gametophores aresupported vertically on Velcro strips held within a clear perspexbox, with their bases resting in liquid. Shoots sampled fromthe field were either continuously exposed to test solutionsvia their cut bases, or by preliminary pulse-immersion. Growthwas assessed by linear extension, or final dry mass, and showeddifferent patterns and sensitivities to heavy metals using thetwo exposure methods. A biologically appropriate assessmentof toxicity was established, using tissue concentrations comparableto material from polluted field sites, by considering the cellularlocation of heavy metals in shoots. A linear relationship wasestablished between apical growth and intracellular Zn concentrationrecovered in the newly produced gametophyte tissue, irrespectiveof the method of exposure or Zn concentration in the remainingor original shoot portion. The limitations and ambiguity associatedwith many heavy-metal monitoring and toxicity studies are addressed,and the advantages and further applications offered by thisgrowth system are discussed. Rhytidiadelphus squarrosus ; growth; heavy metal effects; cadmium; copper; lead; zinc; bioassay     

Introduction: A perspective from the humanities-science boundary

The articles in this special issue range across such influences on climate as solar emissions, orbital precession, atmosphere, oceans, and precipitation, and generally approach, each in some context, human implications of these phenomena. The common underlying theme of all of the papers is the effect the phenomena have on radiation balance as measured by global average temperature. This introductory paper undertakes a formulation of radiation balance theory that makes it serviceable to students of regional science. The objective is to go beyond inference of cause and effect by correlation to causal accounts of cause and effect through regional climatic and cultural processes. This is accomplished primarily by revisualization of the energy system with regions as dependent spatiotemporal entities, and temporally through a protocol for regional episode definition.This special issue ofHuman Ecology consists of the American Anthropological Association Invited Symposium on Global Climate Change.     

ComC is required for the processing and translocation of ComGC, a pilin-like competence protein of Bacillus subtilis

ComGC is a cell surface-localized protein required for DNA binding during transformation in Bacillus subtilis. It resembles type IV prepilins in its N-terminal domain, particularly in the amino acid sequence surrounding the processing cleavage sites of these proteins. ComC is another protein required for DNA binding, which resembles the processing proteases that cleave type IV prepilins. We show here that ComGC is processed in competent cells and that this processing requires ComC. We also demonstrate that the PilD protein of Neisseria gonorrhoeae, a ComC homologue, can process ComGC in Escherichia coli, and that the ComC protein itself is the only B. subtilis protein needed to accomplish cleavage of ComGC in the latter organism. Based on NaOH-solubility studies, we have shown that in the absence of ComC, but in the presence of all other competence proteins, B. subtilis is incapable of correctly translocating ComGC to the outer face of the cell membrane. Finally, we show that ComGC can be cross-linked to yield a form with higher molecular mass, possibly a dimer, and present evidence suggesting that formation of the higher mass complex takes place in the membrane, prior to translocation. Formation of this complex does not require ComC or any of the comG products, other than ComGC itself.