Plant enrichment with stable isotopes

Maximal enrichment of plant tissues with stable isotopes would occur if the mineral in the nutrient solution were totally replaced with the stable isotope throughout the entire growing period. However, this would not be the most efficient use of stable isotopes and could be prohibitively expensive for some stable isotpes such as Zn in quantities needed for a human bioavailability study. 

For the purpose of enriching plants with stable isotopes, it was necessary to develop a hydroponic technique which requires a small amount of nutrient solution per plant and which maintains the same nutrient solution from the addition of the stable isotope until maturity of the plant. The expense of stable isotopes prohibits usings a great volume of nutrient solution or discarding nutrient solution before maximal uptake of the isotope is achieved. 

The electromagnetic separation plant built during World War 11 at Oak Ridge, involved two types of calutrons, alpha and beta. The larger alpha calutrons were used for the enrichment of natural uranium, and the beta calutrons were used for the final separation of U from the pre-enriched alpha product. For the electromagnetic separation process, UO was converted into UCl [10026-10-5] with CCl. The UCl was fed into the calutron for separation. The calutron technique has been used to separate pure samples of and stable isotopes of many other elements. The Y-12 calutron... 

The reverse isotope dilution technique can be applied for accurate determination of the Mg contents in a sample, sample, on applying equation 7, by measuring the isotope ratio of a selected pair of stable isotopes, in a weighed mixmre of the sample with an isotopically enriched CRM. The average atomic masses m and the isotopic ratios R of Mg in the enriched CRM and in nature are known. The method was applied for determination of Mg in plant material using a CRM isotopically enriched with Mg, measuring with an ICP/MS instruments. ... 

Isotopic Tools Tracers. Carbon has three stable or long-lived isotopes 98.9% of earth s C is 12C, -1.1% is 13C (a stable isotope), and about one in a trillion (1 in 1012) carbon atoms is 14C. By enriching or depleting the ratios of the rare isotopes in plants, plant litter, or other organic material put in soil, it is possible to follow the pulse of altered isotopic ratios (and the carbon compounds they were associated with) as they move through the system. 

In order to investigate the distribution and transport of mineral elements in plants by tracer experiments, the aqueous nutrient solution was doped with the highly enriched stable isotopes Mg, Mg, " Ca and (see Figure 9.24 a). The fine focused primary ion beam can be... 

It appears likely that the application of stable isotope techniques to the study of paleonutrition will continue. Carbon isotopes have been shown to be useful to trace the introductions of tropical Ck crops into temperate regions where C3 plants predominate. Other recent studies with carbon isotopes have demonstrated that seafoods are more enriched in than terrestrial foods, and that the proportions of marine vs land-derived foods can be estimated in prehistoric coastal people ( ). Elements other than carbon may demonstrate isotopic distributions that will provide useful dietary information. For example, ratios of... 

Although quantitative analysis of endogenous plant hormones by traditional GC has serious limitations, isotopic dilution analysis by GC-SIM using a single internal standard labelled with a stable isotope, such as H, C or N, is a completely different proposition [3-6]. Because the cost of a simple, computer-controlled, quadrupole-mass spectrometer has fallen substantially, and many highly enriched, isotopically-labelled compounds suitable for use as internal standards in quantitative analysis, can be either synthesized (1) or purchased from commercial sources (see Table 1), capillary GC-SIM is now the quantitative assay of choice in the vast majority of laboratories in which endogenous plant hormones are analysed on a routine basis. 

As is the case with isotopic labeling of molecules, enriched levels of stable isotopes of elements can be used as tracers. Isotopes of elements can be used as nutritional supplements for plants or animals to trace absorption, assimilation, and metabolism of elements (Allen and Georgitis). Processes such as biomethylation of elements like mercury and arsenic in the environment can be studied using isotopically enriched elements. In some cases, methylated metals are more toxic than the inorganic species, and generally accumulate up the food chain. 

The first ever application of a radiotracer in a biological experiment dates back to 1923 when George de Hevesy used Pb to study plant uptake of lead from solution [5]. His seminal work was honored by the Nobel Prize in Chemistry in 1943 and made him the father of isotope tracing, a tool that is still indispensable in virtually any area of scientific research. The first use of a stable isotope to study mineral metabolism was reported in 1963, when Lowman and Krivit injected stable Fe together with radioactive Fe into a human subject to compare the plasma clearance of the two isotopes [6]. However, it was not until the 1980s that stable isotope techniques were explored systematically to study mineral and trace element metabolism in humans. This was not only due to the increasing recognition of health hazards associated with the use of radioisotopes. Mass spectro-metric techniques had to be refined to measure isotope ratios of the heavier elements at a precision suitable for the exploitation of isotopically enriched elements as tracers. Stable isotopic labels are made up from the same isotopes as the natural element, from which they differ only in terms of composition, that is, in the relative abundances of their isotopes. 

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