Hyperaccumulators of metal and metalloid trace elements: Facts and fiction

Background

Plants that accumulate metal and metalloid trace elements to extraordinarily high concentrations in their living biomass have inspired much research worldwide during the last decades. Hyperaccumulators have been recorded and experimentally confirmed for elements such as nickel, zinc, cadmium, manganese, arsenic and selenium. However, to date, hyperaccumulation of lead, copper, cobalt, chromium and thallium remain largely unconfirmed. Recent uses of the term in relation to rare-earth elements require critical evaluation.

Scope

Since the mid-1970s the term ‘hyperaccumulator’ has been used millions of times by thousands of people, with varying degrees of precision, aptness and understanding that have not always corresponded with the views of the originators of the terminology and of the present authors. There is therefore a need to clarify the circumstances in which the term ‘hyperaccumulator’ is appropriate and to set out the conditions that should be met when the terms are used. We outline here the main considerations for establishing metal or metalloid hyperaccumulation status of plants, (re)define some of the terminology and note potential pitfalls.

Conclusions

Unambiguous communication will require the international scientific community to adopt standard terminology and methods for confirming the reliability of analytical data in relation to metal and metalloid hyperaccumulators.     

Analytical surveillance of emerging drugs of abuse and drug formulations

Uncontrolled recreational drugs are proliferating in number and variety. Effects of long-term use are unknown, and regulation is problematic, as efforts to control one chemical often lead to several other structural analogs. Advanced analytical instrumentation and methods are continuing to be developed to identify drugs, chemical constituents of products, and drug substances and metabolites in biological fluids. Several mass spectrometry based approaches appear promising, particularly those that involve high resolution chromatographic and mass spectrometric methods that allow unbiased data acquisition and sophisticated data interrogation. Several of these techniques are shown to facilitate both targeted and broad spectrum analyses, the latter of which are often of particular benefit when dealing with misleadingly labeled products or assessing a biological matrix for illicit drugs and metabolites. The development and application of novel analytical approaches such as these will help to assess the nature and degree of exposure and risk and, where necessary, inform forensics and facilitate implementation of specific regulation and control measures.     

Global marine bacterial diversity peaks at high latitudes in winter

Genomic approaches to characterizing bacterial communities are revealing significant differences in diversity and composition between environments. But bacterial distributions have not been mapped at a global scale. Although current community surveys are way too sparse to map global diversity patterns directly, there is now sufficient data to fit accurate models of how bacterial distributions vary across different environments and to make global scale maps from these models. We apply this approach to map the global distributions of bacteria in marine surface waters. Our spatially and temporally explicit predictions suggest that bacterial diversity peaks in temperate latitudes across the world''s oceans. These global peaks are seasonal, occurring 6 months apart in the two hemispheres, in the boreal and austral winters. This pattern is quite different from the tropical, seasonally consistent diversity patterns observed for most macroorganisms. However, like other marine organisms, surface water bacteria are particularly diverse in regions of high human environmental impacts on the oceans. Our maps provide the first picture of bacterial distributions at a global scale and suggest important differences between the diversity patterns of bacteria compared with other organisms.     

Biosynthesis of C(20) and C(22) Fatty Acids by Developing Seeds of Limnanthes alba: CHAIN ELONGATION AND Delta5 DESATURATION

The storage triacylglycerols of meadowfoam (Limnanthes alba) seeds are composed essentially of C₂₀ and C₂₂ fatty acids, which contain an unusual Δ5 double bond. When [1-¹⁴C]acetate was incubated with developing seed slices, ¹⁴C-labeled fatty acids were synthesized with a distribution similar to the endogenous fatty acid profile. The major labeled product was cis-5-eicosenoate, with smaller amounts of palmitate, stearate, oleate, cis-5-octadecenoate, eicosanoate, cis-11-eicosenoate, docosanoate, cis-5-docosenoate, cis-13-docosenoate, and cis-5,cis-13-docosadienoate. The label from [¹⁴C]acetate and [¹⁴C]malonate was used preferentially for the elongation of endogenous oleate to produce cis-[¹⁴C]11-eicosenoate, cis-13-[¹⁴C]docosenoate, and cis-5,cis-13-[¹⁴C]docosadienoate and for the elongation of endogenous palmitate to produce the remaining C₂₀ and C₂₂ acyl species. The Δ5 desaturation of the preformed acyl chain and chain elongation of oleate and palmitate were demonstrated in vivo by incubation of the appropriate 1-¹⁴C-labeled free fatty acids. Using [1-¹⁴C]acyl-CoA thioesters as substrates, these enzyme activities were also demonstrated in vitro with a cell-free homogenate.     

Effects of cholestyramine on 1,2-dimethylhydrazine-induced enteric carcinoma in germfree rats.

Oral administration of 1,2-dimethylhydrazine (DMH) induced intestinal neoplasms in germfree rats. A supplement of 2% cholestyramine resin in the diet increased the frequency of DMH-induced intestinal tumors and accelerated malignant transformation. Bile acids in the cecal content were determined with and without cholestyramine in order to obtain a correlation between the bile acid metabolism and the enteric carcinogenesis.     

A simple and novel method for radiometric analysis of glucose utilization by adrenal chromaffin cells

Glucose utilization by cells and tissues can be followed by measuring the release of [³H]H₂O from added -[5-³H]glucose, and we have developed a method whereby the whole reaction and assay can be performed in a single scintillation vial. The basic principle behind our new assay is that the released tritiated hydrogen ion in water can be quantitatively exchanged with the hydroxyl proton of simple alcohols such as isoamyl alcohol. The radiolabeled alcohol can then be extracted into an organic solvent to which 2,5-diphenyloxazole and p-bis[2-(5-phenyloxazoyl)]benzene have been previously added. Using this new assay we studied isolated chromaffin cells and found them to utilize glucose at a linear rate for at least 30 min. The assay was precise and reproducible enough to allow detailed analysis of various inhibitors of glycolysis and of oxidative phosphorylation. The new method is simple and rapid, can be done in open test tubes, requires no complex equipment, and is intrinsically highly accurate.