Determined boron isotope fractionation during uptake and transport agrees with proposed mechanisms
Source: BAM, Inorganic Trace Analysis Division
The isotopic composition of elements is not constant but varies on earth and in cosmos. Recent studies show that isotope variations in the biosphere might be even larger than in the geosphere. Such isotope variations typically are reported as so-called delta-values, which is the relative deviation from an internationally accepted standard, because relative measurements can be carried out much more precisely than absolute measurements. In the case of the element boron relatively large isotope variations occur on earth in the order of about 90 ‰. In the beginning of this project it was planned to utilize this huge boron isotope variation for determining the origin of plant-based food. A pilot study on bell pepper and asparagus, however, revealed an intra-plant isotope variation in the range of the inter-plant isotope variation of species from different geographic origin, or even beyond, rendering this approach useless. It was now required to unravel the reasons for this huge intra-plant isotope fractionation, making up nearly one third of the terrestrial boron isotope fractionation. For this several bell pepper plants were grown with different culture media. After ripening of the bell pepper fruits the plants were harvested, cut into pieces especially roots, stem, leaves and fruits, and were immediately frozen. Then the samples were analyzed with a specially developed analytical procedure to obtain the boron isotope variations. Overall the results show an enrichment of 11B, the heavier isotope of both boron isotopes, in higher located plant parts. This systematic increase in 11B isotope amount fraction from the roots to the meristem can be explained by a preferred incorporation of 10B into the cell walls and a preferred transport of 11B to growing meristems by boron transporter molecules. This is in good agreement with the mechanisms proposed by Takano et al. (Nature 420, 2002, 337-340 and others). By a better understanding of boron isotope fractionation in plants, in the future, boron isotope ratios may serve as a tool for investigating plant metabolism, especially boron toxicity and undersupply.
Boron isotope variability related to boron speciation (change during uptake and transport) in bell pepper plants and SI traceable n(11B)/n(10B) ratios for plant reference materials
Sonja Geilert, Jochen Vogl, Martin Rosner, Thomas Eichert
Rapid Communications in Mass Spectrometry, Volume 33, Issue 13, Pages 1137-1147
BAM, Inorganic Trace Analysis division